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ALOHA® - the Oklahoma Department of Environmental Quality

1. Source Toxic Scenarios Fire Scenarios Explosion Scenarios Direct Direct Release Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Puddle Evaporating Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Pool Fire Pool Fire Tank Not Burning Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Jet Fire or Pool Fire BLEVE BLEVE Fireball and Pool Fire Gas Pipeline Not Burning Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Jet Fire Jet Fire 18 Chapter 1 Welcome to ALOHA What about chemicals that are flammable and toxic Many of the chemicals in ALOHA s chemical library are flammable in addition to being toxic and volatile enough to be potential air hazards For those chemicals you can model not only the toxic threat posed by the release of that chemical but also the fires and or explosions that the chemical could potentially cause However ALOHA cannot model these threats at the same time If a flammable and toxic chemical such as acrolein has been released run a toxic gas dispersion scenario first Next run all of the appropriate fire and explosions scenarios Finally consider all of the threat zone plots the estimates will vary with each scenario and any additional site specific data and use that information to decide how you are going to respond to the incident In many situations in
2. 72 Chapter 3 Examples You ll see ALOHA s threat zone plot for this scenario showing three thermal radiation threat zones ALOHA estimates that the red threat zone the worst hazard level will extend 560 yards in all directions the threat distance values are displayed in the Text Summary The orange and yellow threat zones represent areas of decreasing hazard Check the plot legend to see the hazard that each zone represents It is important to realize that there may be additional hazards that are not modeled by ALOHA including hazardous fragments overpressure and secondary fires and explosions Thermal Radiation Threat Zone 0 5 gt 10 0 kW sq m potentially lethal within 60 sec Eg gt 5 0 kW sq m 2nd degree burns within 60 sec gt 2 0 kW sq m pain within 60 sec Check the Text Summary for this release to see a summary of the scenario and the threat zones Text Summary SOURCE STRENGTH BLEVE of flammable liquid in horizontal cylindrical tank Tank Diameter 9 67 feet Tank Length 76 feet Tank Volume 33866 gallons Tank contains liquid Internal Storage Temperature 76 F Chemical Mass in Tank 76 1 tons Tank is 166 full Percentage of Tank Mass in Fireball 166 Fireball Diameter 253 yards Burn Duration 14 seconds THREAT ZONE Threat Modeled Thermal radiation from fireball Red 566 yards 16 6 kW sq m potentially lethal within 66 sec Orange 796 yards 5 6 kW
3. 5 Ask ALOHA to display a threat zone plot showing one or more areas where a hazard toxicity flammability thermal radiation or damaging overpressure may exceed key Levels of Concern LOCs and pose a threat to people and property If three LOCs are chosen ALOHA will display the threat zones in red orange and yellow The red threat zone represents the worst hazard and the orange and yellow threat zones represent areas of decreasing hazard ALOHA can display this threat zone plot on an electronic map of your city using MARPLOT as shown below and ALOHA s threat zones can also be exported to GIS systems MARPLOT Prince William County VA DER File Edit View List Objects Sharing Help v Focus Pt 38 49 24 N 77 38 33 wl in 0 16 mi Central Valley Schog You can also use the Threat at Point feature to obtain specific information about the hazards at points of interest such as schools and hospitals in and around the threat zones ALOHA will display the threat at a point either as a In versions of ALOHA prior to 5 4 the graph or as text For example if you choose to see the term footprint was used instead of threat threat at a point for a toxic gas dispersion scenario zone The two terms are equivalent ALOHA will display a graph showing predicted indoor and outdoor chemical concentrations at the location for the first hour after the release Threat Zones and Footprints You can save ALOHA results
4. ALOHA displays its results in exponential notation whenever numbers are too large to display in decimal notation Exponential notation is a way of displaying a number as a digital number multiplied by a power of 10 In the number 5e3 for example 5 is the digital number and 3 is the power to which 10 is taken Interpret 5e3 as 5 times the quantity 10 taken to the power of 3 which equals 5 000 in decimal notation Likewise interpret 5e 3 as 5 times the quantity 10 taken to the power of 3 which equals 0 005 in decimal notation Interpret 5 2e8 as 5 2 times 10 taken to the power of 8 or 520 000 000 You have asked for a concentration estimate for a point very close to the source ALOHA knows that concentrations of a pollutant are extremely high right at the point of release and drop off as you move downwind It uses equations to approximate what happens in reality Modelers call ALOHA a far field model because these equations much more accurately predict events at distances of more than a few yards from the source than very near the source In fact according to these equations concentration is infinite at the point of release 163 Chapter 5 Troubleshooting I want to modify a chemical but I can t change some properties they appear grey I am trying to model the release of gas from a gas pipeline but ALOHA says the pipe is too short It tells me that the length must be at least 200 times the diameter of th
5. Hazardous fragments Heat of combustion Heavy gas The roughness of the ground over which a pollutant cloud is moving Degree of ground roughness depends on the size and number of roughness elements which can range in size from blades of grass to buildings Ground roughness generates air turbulence which acts to mix air into the pollutant cloud and dilute the pollutant gas When all else is equal a threat zone will be smaller when you choose a larger ground roughness value The temperature of the ground beneath an evaporating puddle ALOHA uses your value for ground temperature to estimate the amount of heat that is transferred from the ground to an evaporating puddle The physical composition of the ground beneath a puddle The ground type is especially important when a refrigerated liquid spills to form a boiling puddle In such cases often more of the heat required for puddle evaporation is supplied by the ground rather than the atmosphere One of the major hazards associated with any explosion Hazardous fragments are flying debris propelled by the explosion s pressure wave Hazardous fragments come from two primary sources container fragments and debris from the surrounding area Energy released as heat when a chemical undergoes complete combustion with oxygen that is burns completely The heat of combustion is usually determined experimentally The units are expressed as energy amount of fuel e g J kg or BTU Ib
6. The unbroken end of the pipe is C yds connected to infinite tank source C closed off Select pipe roughness Smooth Pipe C Rough Pipe Cancel 146 Chapter 4 Reference Pipe pressure If the pipeline is connected to Pipe Preseureend HoleSize a very large infinite reservoir use the Input pipe pressure pressure within the reservoir as your value Pressureis 58 psia for pipe pressure If gas is escaping from a finite closed off section of pipeline enter the Input pipe temperature pressure within that pipe section Unknown assume ambient e Pipe temperature Indicate the temperature obese ere we of the pipe contents in either of two ways a click Unknown assume ambient if you do Pde not know the temperature ALOHA will then ass ppe damer use the ambient air temperature or b type shies JE square in the temperature of the pipe s contents in the pipe temperature box then select appropriate _ Cancel units either degrees Fahrenheit or Celsius e Hole size If the pipeline is connected to a very large infinite reservoir ALOHA assumes that the pipe has been completely sheared off so that the hole diameter equals the pipe diameter If only a closed off length of the pipeline is leaking you can choose to a allow ALOHA to use the pipe diameter as its value for the hole diameter or b enter a value for the area of the hole if the hole is smaller in area than the pipe diameter Source st
7. in an industrial area you determine that the vapor cloud could be ignited if it ignites by a mechanical spark Select ignited by Cancel spark or flame C congested difficult to walk through e g pipe rack dense forest uncongested easy to walk through e g residential neighborhood 7 The flammable area is slightly congested However slightly congested doesn t seem to fit into either of ALOHA s congestion categories After reading the on screen help you are fairly sure that you should choose the uncongested option because it describes the majority of the cloud However you also realize that congestion level can affect the severity of a vapor cloud explosion so you decide to model the explosion twice once with each congestion option so that you can compare the potential explosions Begin by selecting the uncongested option because you feel it is the most accurate guess Click OK An Overpressure Level of Concern dialog box appears 78 Chapter 3 Examples 8 You want to know the overpressure threat for the vapor cloud explosion Keep ALOHA s default LOCs and check that Show confidence lines only for the longest threat zone has been selected Click OK ALOHA will display a threat zone plot for this release Overpressure Level of Concern Select Overpressure Level of Concern Red Threat Zone Loc 8 0 psi destruction of buildings X Orange Threat Zone 13 5 psi serious injury likely Yello
8. A gas cloud that is denser than the air around it There are several reasons why a gas forms a heavy gas cloud or behaves like a heavy gas 1 because its molecular weight is greater than that of air about 29 kilograms kilomole 2 because it is stored cryogenically refrigerated or 3 because aerosols form in sufficient quantity during a release to cause the mixture to behave like a heavy gas 177 Glossary IDLH Infinite tank source Instantaneous source Inversion Jet fire The Immediately Dangerous to Life or Health IDLH level is a limit originally established for selecting respirators for use in workplaces by the National Institute for Occupational Safety and Health NIOSH A chemical s IDLH is an estimate of the maximum concentration in the air to which a healthy worker could be exposed without suffering permanent or escape impairing health effects NIOSH Web site http www cdc gov niosh A case in which a gas pipeline is connected to a reservoir that is so large that gas escapes from the broken end of the pipeline at a constant rate for an indefinite period of time A very short term release ALOHA assumes that an instantaneous release lasts 1 minute An atmospheric condition in which an unstable layer of air near the ground lies beneath a very stable layer of air above The height of the abrupt change of atmospheric stability is called the inversion height An inversion can trap pollutant gases below the
9. CARBONYL FLUORIDE csi 2 Select Pure Chemicals at the top of the ORANIN E E window this should be the default Find Add CHLORINE in the list quickly type the CHLORINE PENTAFLUORIDE a napr CHLORINE TRIFLUORIDE odi characters ch l to locate chlorine more CHLOROAC ETONE rapidly in the list click on this name CHLOROACETONITRILE Delete CHLOROACETYL CHLORIDE then click Select CHLOROBENZENE P CHLOROBENZOTRIFLUORIDE Help Describing the weather When entering weather information in ALOHA you must choose whether you are going to enter weather information manually or from a portable monitoring or SAM station In this example you ll enter information manually 1 Inthe SetUp menu point to Atmospheric then select User Input Chemical Ctri H The first Atmospheric Options dialog ATER box appears Source b SAM Station k 2 The windis travelling from the south at a speed of 5 miles per hour mph Type 5 in the wind speed box then select mph Type S in the wind Atmospheric Options direction box Wind Speed is 5 C knots mph meters sec _ Help Wind is from S Enter degrees true or text e g ESE Calculation Options 3 The wind conditions were measured at a height of 10 meters this is the height spe i Sera reer gt Enay ho C feet at which the National Weather Service a AN ae alta meters usually takes measurements Select the tower icon in the Measurement Height section Notic
10. Each line on the diagram represents a 5 minute running average speed and direction Each line is drawn from the center out towards the direction to which the wind is blowing Line length indicates wind speed The two concentric circles on the diagram represent wind speeds of 10 and 20 miles per hour mph if you have indicated a preference for English units or 5 and 10 meters per second m s if you indicated a preference for metric units indicate your units preference by choosing Display Options from the Display menu The length of each line on the diagram indicates wind speed For example a line drawn from the center of the diagram out to the 10 miles per hour circle represents an average wind speed of 10 miles per hour P Wind Rose 20 The most recent average wind value is represented 13 9 mph on the diagram by a darker line The most recent 5 minute average wind speed is displayed below the diagram Monitoring a long term release You may sometimes use a SAM with ALOHA to monitor weather conditions during a long term release such as a slowly evaporating pool of toxic liquid or a potential spill When you do so bear in mind that although your SAM is providing current weather information other ALOHA inputs may become out of date during the course of the response as conditions change At least once each hour assess whether you need to adjust important model inputs that could affect ALOHA s estimates of source strength or cl
11. Generally wind direction is least predictable when wind speed is low To show how much a dispersion threat zone s position could change if the wind were to shift direction under the particular weather conditions that you enter ALOHA draws two dashed lines one along each side of the threat zone ALOHA predicts that about 95 percent of the time the wind will not shift direction enough to move the hazard outside of either line The wider the zone between the lines the less predictable is the wind direction and the more likely it is to change substantially At the lowest wind speeds acceptable to ALOHA about 2 knots or 1 meter per second at a height of 10 meters these lines form a circle to indicate that the wind could blow from any direction Very stable atmospheric conditions Under the most stable atmospheric conditions most common late at night or very early in the morning there is usually very little wind and almost no mixing of the released chemical with the surrounding air Gas concentrations within the cloud can remain high far from the source The accidental release of methyl isocyanate gas at Bhopal India in 1984 is an example of what can happen under very stable atmospheric conditions Thousands of people died including many who were far from the release In a very stable atmosphere a chemical cloud will spread out in the same manner as cream poured into a coffee cup The cream will dilute and spread slowly into the coffee but it wi
12. User IN PU bape enne r E A EEEN eE sve EEEE AEEA TEATE E 113 Wind speed direction and measurement height s ssssssseessseseseseeeeseee 114 Ground TOUS BMESS sles errata o e E E 116 Cloud COVET isisi eecsransecel ais ien eps Aa SE Ena ES eel AEEA E SEa O ETEN p 118 Aar temperaturen eia E oe a E EE E a eis 118 Stability elas Seenen iea a a a E E E 119 Inversion b ightoanonin enteno E AE AE RE E aT 120 Hamidit cece fhe cls e Vt Sake Nal sls e e e aa e 121 SAM Station erien onia n RRA Ree Seer oe eee eS E a OREO ETT A 122 Choosing a SAM ceins erinan eei eiee a Ter ae E Epi ia is 122 Transmitting SAM data to ALOHA sssssssessesssesssesssssessseessresseesseresseessres 122 Using a SAM during an incident 000 0 cececseececeseceessceeseececnseeeeeceees 123 Choosing the correct port for receiving SAM data 123 Choosing a radio Mequeney 2 c0000o ceendig dee oh wee Ba oie Geek 123 Setting up ALOHA when you re using a SAM eee eceeeeeeeeereeeneeees 123 SAM Options scosse cavsckceascacacen pansate eia Epa EE E A E TESA ETEEN S 124 PCI V CAA ec te tae eilccig eE EE EAE A Ae i 125 POA MAAS ta ees poe irate diel a ccd anh a ee ea feed D E cdc nel Mi rege 126 Processed Datawis2 x indecsit ceeds eesti eed ee ei beat ade ei a aeai Eas 126 Wind ROSE ors eas ede iets Bde ea See Be edie 127 Monitoring a long term release eeeeeeceeeeeceeeeceeeeeceeeeeceeeeeceseeeeeeeeees 127 OUNCE dese cee asraon es Upped hee Maula choos Deal ede ANSEES EES AS
13. depending on the type of release that you have chosen Source strength graphs for the two types of estimates differ in appearance 156 Chapter 4 Reference Constant source strength Release rate for a Direct source whether it s instantaneous or continuous will remain constant for the duration of the release ALOHA expects an instantaneous release to last for 1 minute and a continuous release to last for up to 1 hour Graphs of either type of Direct release look like the plot shown below F Source Strength Release Rate pounds minute 80 minutes Variable source strength Source strength predicted by the Puddle Tank or Pipe source options can change over time For example consider the rate of release of a pressurized gas from a tank rupture Initially the chemical escapes rapidly through the rupture As the tank pressure drops the rate of release slows If you model such a release using ALOHA you ll see a line that descends in steps on the source strength graph F Source Strength Release Rate pounds minute Z minutes 157 Chapter 4 Reference Source strength averaging ALOHA predicts source strength as a series of hundreds of brief timesteps These values must be averaged into fewer steps so that calculations can be completed quickly For releases into the atmosphere ALOHA averages the series of timesteps into between one and five release rates that are each for a time period of at le
14. escape together from a ruptured tank or pipeline as a two phase flow Many substances that are gases under normal pressures and temperatures are stored under high enough pressures to liquefy them For example ammonia is a gas at normal pressures and temperatures but is often stored under pressure as a liquid When a rupture or broken valve causes a sudden pressure loss in a tank of liquefied gas the liquid boils violently the tank contents foam up and the tank fills with a mixture of gas and fine liquid droplets called aerosol When such a two phase mixture escapes from the container the release rate can be significantly greater than that for a purely gaseous release The atmosphere is unstable when substantial air turbulence exists so that there is a strong tendency for air to be mixed into a dispersing pollutant cloud The Upper Explosive Limit UEL also called the Upper Flammability Limit is the maximum concentration of fuel in the air that can sustain a fire or an explosion if an ignition source is present If the concentration is above the UEL there is not enough oxygen to sustain a fire or an explosion it is too rich much like an engine that cannot start because it has been flooded with gasoline The UEL is determined experimentally using standard temperature and pressure settings Additionally if the fuel concentration in the air falls below the Lower Explosive Limit LEL then a fire or an explosion cannot occur An
15. greater than 10 cm In such cases ALOHA assumes Z to be 10 cm When ALOHA makes its Gaussian calculations if you enter a Z value of 20 cm or more ALOHA uses the Urban or Forest roughness parameters If you enter a Z value of less than 20 cm ALOHA uses the Open Country roughness parameters If you prefer to type in a value for roughness length Z you can refer to Table 4 4 Note that roughness length is not a simple function of the height of the roughness elements in an area Table 4 4 Surface Roughness Z Equivalences from Brutsaert 1982 Surface description Z em Mud flats ice 0 001 Smooth tarmac airport runway 0 002 Large water surfaces average 0 01 0 06 Grass lawn to 1 cm high 0 1 Grass airport 0 45 Grass prairie 0 64 Grass artificial 7 5 cm high 1 Grass thick to 10 cm high 2 3 Grass thin to 50 cm 5 Wheat stubble plain 18 cm 2 44 Grass with bushes some trees 4 1 2 m high vegetation 20 Trees 10 15 m high 40 70 Savannah scrub trees grass sand 40 Large city Tokyo 165 Chapter 4 Reference Cloud cover ALOHA needs a value for cloud cover the proportion of the sky that is covered by clouds in order to estimate the amount of incoming solar radiation at the time of a chemical release Solar radiation is an important influence on puddle evaporation rate because heat from the sun can warm a puddle and speed up evaporation In th
16. in the air temperature box then select F 7 ALOHA uses the wind speed cloud cover and date and time information Atmospheric Options 2 Air Temperature is 80 Degrees F CC Help Stability Classis Help C 4 CB DE c Override Inversion Height Options are Help G No Inversion C Inversion Present Heightis feet that you ve entered to automatically C meters select atmospheric Stability Class D Select Humidity Help representing conditions of neutral bral ie atmospheric stability c C ORC entervalue 75 8 There is no low level inversion Check medium dry 0 100 to be sure that No Inversion is Cancel selected 9 The relative humidity is about 75 percent Choose the second option from the left the option between the wet and medium options Notice that ALOHA has filled in a value of 75 percent Click OK The information that you have entered into ALOHA appears in the Text Summary Ignore ALOHA s estimate of building exchange rate since you are not considering infiltration into buildings Text Summary SITE DATA Location BATON ROUGE LOUISIANA Building Air Exchanges Per Hour 6 58 unsheltered single storied Time August 26 2666 2236 hours CDT user specified CHEMICAL DATA Chemical Name BENZENE Molecular Weight 78 11 g mol ERPG 1 56 ppm ERPG 2 156 ppm ERPG 3 1666 ppm IDLH 566 ppm LEL 12666 ppm UEL 86666 ppm Carcinogenic risk see CAMEO Ambient Boiling Point 176 1 F Vapor Pressu
17. water and or water vapor to produce hydrogen chemical is reactive and will describe the type of reaction chloride phosphoric acid and heat ALOHA and reaction products to expect cannot accurately predict the air hazard if a reaction occurs If you choose to model the chemical ALOHA will place a eh eel ls similar warning in the Text Summary window as an a Ham additional reminder Chemical information in the Text Summary window Review the Text Summary for information about the chemical you ve selected For example values for some properties of benzene appear in the Text Summary below You can see for example that benzene s boiling point is well above most ambient temperatures so you can expect to encounter it as a liquid Text Summary CHEMICAL DATA Chemical Name BENZENE Molecular Weight 78 11 g mol ERPG 1 56 ppm ERPG 2 156 ppm ERPG 3 1666 ppm IDLH 566 ppm LEL 12666 ppm UEL 86666 ppm Carcinogenic risk see CAMEO Ambient Boiling Point 176 1 F Vapor Pressure at Ambient Temperature 6 13 atm Ambient Saturation Concentration 134 835 ppm or 13 5 Some items in the chemical information summary need some explanation e Ambient Saturation Concentration Within a confined space such as a cargo hold or warehouse at a given temperature the ambient saturation concentration is the maximum concentration in the air that the vapor evaporating from a liquid pool may reach If a chemical has a high ambient saturat
18. 17 ALOHA can choose a dispersion model for YOU eee eeeeeeeseeeeeeeeeeeeee 18 Introduction to fires and CXplOSiONS eee eeseceseceseesseceseceeeeesseecsaeceseeeseeeeaeecsaeceeenseeeeaees 18 W Hat 18 fre iroura Sabet aos A REEE tailed a hii 19 Thermal Radiation Levels of Concern ee eeeeeeeesseceseceseeeeseecnaeenseeeees 20 What Isan eXplosion Zisis aT E e E TER 21 Oyerpres S re min a aa ead oa A E todas 21 Overpressure Levels of Concern ssessesessssessressessesseeeeseeesseessesseeesseee 22 Hazardo s fragments nni pr e e EI EEE E take 23 Types of fire and explosion scenarios sseeeseseeeeeseessrsressttsesresstesesrresresetsreesreseesereseesee 23 Jet fire Siantan ia E S E NEEESE S o E S 24 POOLTE niria aa a S T R S I O 24 BLE VES crire ooe a el iat ae ea 25 Fireballs iii e e Paes pal asta e hs a idae i lse tyad aea ara 25 Explosion and hazardous fragments eeseseseeeeeseeesesresseesrerressersessresressesee 25 Flash fires flammable area wdtensckieiidnks niai a a oak aa E A 26 Table of Contents Vapor cloud explosions sorrire es ee a i ia 26 Deflagration and detonation jie jcticetl enti i ee eee 27 Congestion and confinement seseseeesesseeseeeresresseserserssresseseresressessessressesee 27 ALOHA SHimitatons ee E E E ects E E asa 28 Conditions that can produce unreliable results 0nnnsssnssessseeeesseessesseesseesseesseeso 28 Very low wind Speeds s cccssissscacisssaveisas
19. 31 1900 0 23 0 59 Cancel Help 86 Chapter 3 Examples 10 To choose the chemical that is being released chlorine select Chemical from the SetUp menu A Chemical Information dialog box appears with a list of the chemicals in ALOHA s chemical library Check to be sure that Pure Chemicals is selected at the top of the window this should be the default Find CHLORINE in the list quickly type the characters ch to locate chlorine more rapidly in the list click on this name then click Select Entering weather information Chemical Information View Pure Chemicals C Solutions gt Cancel CARBON TETRAFLUORIDE CARBONYL FLUORIDE CARBONYL SULFIDE CHLORAMINE CHLORINE Add CHLORINE DIOXIDE CHLORINE PENTAFLUORIDE CHLORINE TRIFLUORIDE CHLOROACETONE CHLOROACETONITRILE CHLOROACETYL CHLORIDE CHLOROBENZENE P CHLOROBENZOTRIFLUORIDE Now that you ve selected the location time and chemical you must provide information about weather conditions and ground roughness 1 In the SetUp menu point to Atmospheric then select User Input The first Atmospheric Options dialog box appears The wind is travelling from the east at a speed of 6 miles per hour Type 6 in the wind speed box then select mph Type E in the wind direction box The wind conditions were measured at a height of 3 meters Type 3 in the measurement height value box and select meters T
20. 66 sec 83 Chapter 3 Examples You have already compared the plots for the flammable area and the vapor cloud explosion so now you want to compare the thermal radiation threat zone plots and the Text Summary screens from the BLEVE and jet fire scenarios Below the BLEVE threat zone plot is shown on the left and the threat distances from the Text Summary screens for all of the scenarios are summarized in a table The BLEVE red threat zone the worst hazard level is estimated to extend 560 yards in all directions The jet fire red zone is only predicted to extend about 50 yards in all directions However the BLEVE will last about 14 seconds whereas the jet fire is predicted to last over an hour When considering thermal radiation hazards it is important to consider both the thermal radiation level and the length of time over which someone might be exposed to that level WI Thermal Radiation Threat Zone 150 _ 200 100 0 2 300 yards gt 10 0 kW sq 8 gt 5 0 k 2q m gt 2 0 kU 3q n gt 10 0 kW aq 5 gt 5 0 k 3q m gt 2 0 kU 3q n potentially lethal within 60 sec potentially lethal within 60 sec ind degree burns within 60 sec pain within 60 sec ind degree burns within 60 sec pain within 60 sec Red Orange Yellow Scenario Threat Mleled Threat Zone Threat Zone Threat Zone BLEVE Thermal radiation 560 yards 790 yards 12
21. A rr Figure 4 1 Effects of solar radiation on atmospheric stability Stability class has a big effect on ALOHA s prediction of the threat zone size for dispersion scenarios Under unstable conditions a dispersing gas mixes rapidly with the air around it ALOHA expects that the cloud will not extend as far downwind as it would under more stable conditions because the pollutant is soon diluted to below your LOC and ALOHA will display a shorter threat zone than it would for more stable conditions UNSTABLE NEUTRAL STABLE a ae M a weak winds strong winds weak winds AN SUNSHINE NIGHTTIME STRONG HEATING A MUCH TURBULENT MIXING In rare cases stronger winds may be associated with F stability Figure 4 2 Stability class and mixing of a pollutant cloud 119 Chapter 4 Reference ALOHA uses Table 4 5 based on Turner 1994 to automatically choose the stability class that best represents the weather conditions that you enter If more than one stability class fits the conditions that you indicate ALOHA selects the most stable of these classes For example if both A and B fit the conditions ALOHA selects B However you can click A if you believe this class to be more appropriate Buttons for stability classes inappropriate for those conditions are unavailable for selection Table 4 5 Stability class and wind speed Wind Speed Day Incoming Solar Radiation Nig
22. English units Source Strength cCtril G C Metric units Tile Windows Cancel Stack Windows Display Options Ctrl 42 Chapter 2 Learning the Basics Creating a threat zone plot To obtain a threat zone estimate you must first choose at least one Level of Concern LOC ALOHA allows you to choose up to three LOCs for a single scenario For toxic gas dispersion scenarios like this one an LOC is a threshold concentration of the gas usually the concentration above which a hazard is believed to exist For each LOC you choose ALOHA estimates the region or threat zone where the ground level pollutant concentration may exceed your chosen level at some time after a release begins ALOHA superimposes those threat zones estimates and displays them on a single composite threat zone plot each threat zone is shown in a different color The red threat zone represents the worst hazard and the orange and yellow threat zones represent areas of decreasing hazard Choosing an LOC No LOC represents an exact line between hazardous and non hazardous conditions because people differ in their sensitivity to chemicals for example old sick or very young people may be more sensitive to chemicals than healthy adults and other hazards An LOC that s appropriate for one person may be too high for somebody else When you use an LOC in ALOHA familiarize yourself with its definition to be sure it s appropriate for the work that you re doi
23. Length 5 32 feet Tank Volume 566 gallons Tank contains liquid Internal Temperature 86 F Chemical Mass in Tank 1 82 tons Tank is 166 full Circular Opening Diameter 6 inches Opening is 16 inches from tank bottom Max Puddle Diameter Unknown Max Flame Length 26 yards Burn Duration 2 minutes Max Burn Rate 1 616 pounds min Total Amount Burned 3 682 pounds Note The chemical escaped as a liquid and formed a burning puddle The puddle spread to a diameter of 15 6 yards 62 Chapter 3 Examples 8 Choose Source Strength from the Display menu to see the source strength graph for this scenario The graph shows the predicted averaged burn rate F Source Strength Burn Rate pounds minute 2 000 minutes ALOHA estimates that the pool fire would last just under 2 and a half minutes In the Text Summary ALOHA listed the burn duration as 2 minutes ALOHA rounds duration estimates to the nearest whole minute on the Text Summary screen but uses the more precise source strength value in its threat calculations The increase in burn rate for the first minute and a half is due to the growing puddle size as the chemical continues to leak from the tank Choosing LOCs and creating a threat zone plot for the pool fire 1 Choose Threat Zone from the Thermal Radiation Level of Concern Display menu A Thermal Select Thermal Radiation Level of Concern Radiation Level of Concern Red Threat Zone dialog box appears Loc
24. Nevertheless the United States Government does not warrant accuracy or completeness is not responsible for errors and omissions and is not liable for any direct indirect or consequential damages flowing from the recipient s use of ALOHA The ALOHA software is being distributed as is and the United States Government does not make any warranty claims either express or implied with respect to the ALOHA software its quality accuracy completeness performance merchantability or fitness for any intended purpose Indemnification Non governmental recipients shall indemnify and save harmless the United States and its agents and employees against any and all loss damage claim or liability whatsoever due to personal injury or death or damage to property of others directly or indirectly due to the use of ALOHA by the recipient or any other act or omission of the recipient including failure to comply with the provisions of these terms and conditions Editing Any unauthorized editing or alteration of ALOHA chemical data or information provided by the United States Government will result in the termination of the agreement between recipient and the United States Government Upon receipt of notice of termination the recipient shall immediately return all ALOHA information to EPA NOAA including all documents and all copies of software containing ALOHA information Maintenance Recipients should keep EPA NOAA informed of any changes t
25. U S state or territory C InU S Notin U S Enter approximate elevation Elevation is 0 Ct Cm Enter approximate location deg min Latitude 32 18 CNCS Longitude 64 40 CE CW Cancel Next you ll see the Foreign Location Input dialog box Type the country name then the number of hours that local standard time at the location differs from Greenwich Mean Time GMT This time offset value should be positive if the location is in the western hemisphere North and South America and negative if it s in the eastern hemisphere Europe Africa Asia and Australia 103 Chapter 4 Reference Click the appropriate button to indicate whether standard or daylight savings time is currently in effect at this Foreign Location Input location ALOHA automatically switches the time Country name Bermuda setting for U S cities from Standard to Daylight Savings Time using the date on your computer s clock but it Offset from local STANDARD time to GMT 2 hours does not automatically make this change for locations Is current model time standard or daylight savings time outside the U S Be sure to change the time setting manually whenever time at a non U S location switches between daylight savings and standard time Once you Cancel Help i X have entered all necessary information about a new location click OK Click Select to add the location to the library Click Cancel only if you decide not to
26. You wish to know the hazard Input Y the crosswind distance jo C meters value you could expect if the wind were to shift ue and carry the cloud of escaping chemical directly otal Hep towards the hospital To get that estimate you would use ALOHA to obtain threat at a point results for a location a half mile downwind and with a crosswind distance of 0 miles These results represent the worst case hazard levels that could develop at any point one half mile downwind of the source should the wind shift to blow the cloud towards that point Note When you use relative coordinates ALOHA will remember the location of the point that you have specified in terms of its downwind and crosswind distance to the source Therefore the geographic location of the point that you have specified to ALOHA will move when the wind direction changes A point specified in this manner follows the wind If you select your Threat at Point by double clicking on its location within the threat zone window ALOHA will use relative coordinates to track your location Threat at Point results Once you designate a location ALOHA will display its estimate of the threat at a point either as a graph or as text For example if you choose to see the threat at a point for a toxic gas dispersion scenario ALOHA will display a Concentration at Point graph 154 Chapter 4 Reference The Concentration at Point graph displays ground level chemical concentrations in indoor
27. a value for either the tank pressure or the amount of gas either as mass or as volume at the Standard Temperature and Pressure of 1 atmosphere and 0 C then select appropriate units Click OK If you enter a value for tank pressure ALOHA will automatically estimate the mass in the tank Once you have entered values for tank size temperature and either pressure or amount of chemical ALOHA will check to be sure that the chemical is a gas If the tank temperature is below the chemical s boiling point or if the tank pressure is high enough to liquefy the chemical ALOHA will warn you that your chemical is not a gas If this happens click Cancel to return to the previous dialog box click Tank contains liquid then continue Chemical of unknown state in a tank If you are unsure whether a chemical in a tank is a gas or liquid and Mass of Chemical in Tank For a chemical of unknown state you clicked Unknown when asked to identify chemical the chemical mass is required state you will need a value for the total mass weight of The amount of C pounds chemical in the tank in order to run ALOHA ALOHA uses Seen j70 1 Be eS di the tank is kilograms this value along with information about the chemical s properties and the temperature in the tank to predict the Cancel Help chemical s state and the amount of chemical that could be X released Type in the mass of chemical in the tank then select units of pounds kilograms or ton
28. above ground is Help q C feet E A 10 i A OR enter value IC CG Ground Roughness is Help Open Country C C Urban or Forest OF Input Roughness Zo C Open Water A chemical cloud generally travels farther across open country and open water than over an urban area or a forest This is because it encounters fewer smaller roughness elements to create turbulence 116 Chapter 4 Reference Choose the dominant category of ground roughness in the area where the pollutant cloud may travel For example if 70 of the area is urban or forest and 30 is open country click Urban or Forest If you can t easily determine the dominant category run ALOHA once with each category selected to get an idea of the possible range in threat zone size If something such as a tall building is very large relative to the pollutant cloud it is likely to be an obstacle that diverts a pollutant cloud rather than a roughness element that generates turbulence For example in a downtown area on a Sunday morning with no cars on the streets the best ground roughness category for a small release may be Open Country In this case the buildings are obstacles and the street is the roughness the pollutant cloud will experience How does ALOHA interpret your Z value It depends on whether it uses Gaussian or heavy gas dispersion calculations When ALOHA makes its heavy gas calculations it uses the Z value that you entered unless it is
29. amp Time Ctrl E SOUTH DAKOTA Check to be sure that this name is highlighted then click Select Location Information SHERMAN TEXAS SIOUX FALLS SOUTH DAKOTA SMITHTOWN NEW YORK SNOHOMISH WASHINGTON Cancel SOMERSWORTH NEW HAMPSHIRE SOMERYILLE MASSACHUSETTS SOUTH BEND INDIANA SPARKS NEVADA SPARTANBURG SOUTH CAROLINA SPOKANE WASHINGTON SPRINGFIELD ILLINOIS ST ALBANS WEST VIRGINIA ST CHARLES MISSOURI ST JOSEPH MISSOURI ST LOUIS MISSOURI Central Valley Elementary School is located about 1 500 yards downwind of the treatment plant ALOHA uses information about building type along with other information such as wind speed and air temperature to determine indoor infiltration rate and to estimate indoor concentration at a location of concern To estimate infiltration rate into a building ALOHA assumes that all doors and windows are Date amp Time Ctrl E closed Choose Building Type from the SiteData menu An Infiltration Building Parameters dialog box appears Location Ctrl L Building Type 34 Chapter 2 Learning the Basics 6 The school is a single storied building surrounded mostly by open fields Check to be sure that Single storied building and Unsheltered surroundings are selected Click OK Infiltration Building Parameters Select building type or enter exchange parameter Enclosed office building _Help_ Single storied building Double storied building No
30. and are conservative enough for the uses to which you re putting your ALOHA results You make a conservative choice when the option is more likely to produce an overestimate of the hazard rather than an underestimate 47 Chapter 2 Learning the Basics Here s how the Text Summary window should look now that you have completed your work with this example scenario note that depending on the type of computer you use some of the numbers that you see on your screen may be slightly different than those in the following figure Text Summary SITE DATA Location SIOUX FALLS SOUTH DAKOTA Building Air Exchanges Per Hour 6 43 unsheltered single storied Time June 25 2066 1436 hours CDT user specified CHEMICAL DATA Chemical Name CHLORINE Molecular Weight 76 91 g mol AEGL 1 66 min 6 5 ppm AEGL 2 66 min 2 ppm AEGL 3 66 min 26 ppm IDLH 16 ppm Carcinogenic risk see CAHEO Ambient Boiling Point 31 2 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 666 ppm or 166 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 5 miles hour from S at 16 meters Ground Roughness open country Cloud Cover 3 tenths Air Temperature 72 F Stability Class B No Inversion Height Relative Humidity 56 SOURCE STRENGTH Leak from short pipe or valve in horizontal cylindrical tank Non flammable chemical is escaping from tank Tank Diameter 2 5 feet Tank Length 6 8 feet Tank Volume 25
31. and dispersion option Property Direct Puddle Tank Pipeline pra Gaussian Chemical Name Molecular Weight Normal Boiling Point lt gt Critical Pressure lt gt O Critical Temperature lt gt o Gas Density Normal Freezing Point Gas Heat Capacity 4 Liquid Heat Capacity Heat of Combustion F F F F Vapor Pressure ek Required property value lt gt Required if release rate or amount is expressed in volume units gallons liters or cubic meters Required if vapor pressure is not entered F Required if the chemical is flammable and you want to run scenarios where it may catch on fire Required if critical temperature and critical pressure are not entered Note For some fire and explosion scenarios you may also have to enter explosive limits To calculate the flammable areas of a flash fire ALOHA must have the LEL Lower Explosive Level To model a vapor cloud explosion ALOHA must have the LEL and the UEL Upper Explosive Limit Chapter 4 Reference Adding a chemical to the library Select Chemical from the SetUp menu then click Add on the dialog box that appears Type the chemical s name in the Chemical Name box Next type its molecular weight in grams per mole in the molecular weight box Then add values for all other properties that you ll need to run ALOHA see Table 4 1 on page 111 to see whi
32. beginning with co Scroll down a little farther until you see COLUMBIA SOUTH CAROLINA Click on this name to highlight it then click Select Location Information CINCINNATI OHIO a Select CLEVELAND OHIO Le CLIFTON NEW JERSEY CLOQUET MINNESOTA Cancel COLLEGE PARK MARYLAND COLORADO SPRINGS COLORADO Add COLUMBIA MARYLAND COLUMBIA MISSOURI Modify COLUMBUS OHIO _ CONCORD CALIFORNIA CONCORD MASSACHUSETTS Delete CONCORD NEW HAMPSHIRE E CONROE TEXAS CONWAY NEW HAMPSHIRE Help In this example you will not modify the default building type settings because you will not assess indoor concentration at specific locations 5 Select Date amp Time from the SiteData menu A Date and Time Options dialog box appears 6 The release occurs at 12 30 p m on June 25 2006 Select the Set a constant time option Enter the month day year hour and minute for this scenario press Tab to move from one box to the next ALOHA requires you to convert the time of day into 24 hour time click Help to learn how to convert time values Click OK Date and Time Options You can either use the computer s internal clock for the model s date and time or set a constant date and time C Use internal clock Seta constant time Input a constant date and time Month Day Year Hour Minute 1 12 1 31 1900 0 23 0 59 Cancel Help 67 Chapter 3 Examples 7 To choose the chemical that is
33. by volume E Cancel Help 5 The chlorine is leaking from a half inch diameter valve Check to be sure that Circular opening is selected Type 0 5 in the opening diameter box and select inches Choose the Short pipe valve option Click OK A Height of the Tank Opening dialog box appears Area and Type of Leak Select the shape that best represents the shape of the opening through which the pollutant is exiting C va Echni Circular opening C Rectangular opening inches C feet Opening diameter 0 5 C centimeters C meters Is leak through a hole or short pipej valve C Hole Short pipejvalve Cancel Help X 39 Chapter 2 Learning the Basics 6 The leaking valve is located at the center of one end of the tank Type 50 in the percent of the way to the top of the tank box Notice that ALOHA fills in the other values Click OK Height of the Tank Opening 4 The bottom of the leak is 1 25 Cin Cft C cm Cm lig level above the bottom of the tank m O l 50 of the way to the top of the tank Cancel Help ALOHA then calculates the rate of release of chlorine from the tank the duration of the release and the total amount released You ll see these calculation results in the Text Summary window and in the source strength graph Choose Source Strength from the Display menu to see the source strength graph for this scenario The graph shows the predicted averaged release
34. chlorine would arrive at the school in about 7 minutes that s when the outdoor concentration line begins to rise steeply on the graph under the conditions of this scenario Notice that the indoor concentration is predicted to remain much lower than the outdoor concentration as long as the school s doors and windows are closed You also can see that ALOHA predicts that outdoor concentration would exceed one LOC AEGL 2 for this scenario only briefly but will exceed a lower LOC AEGL 1 for much longer The indoor concentration does not exceed any of the LOC values however it does approach the AEGL 1 LOC for a significant period of time At this level people inside the building may begin to experience notable discomfort irritation or other temporary effects Bear in mind that no LOC represents an exact line between hazardous and non hazardous conditions because people differ in their sensitivity to chemicals for example old sick or very young people may be more sensitive to chemicals than healthy adults and other hazards People who are more sensitive to the chemicals may experience more serious health effects than those predicted for the AEGL 1 level even though that level was not exceeded in the hour after the release When you use ALOHA in planning or response you may wish to compare predicted concentrations with other toxic thresholds besides AEGLs Be sure that the LOCs that you choose reflect the hazard that you are concerned about
35. develops Ground roughness is determined by number and size of roughness elements present in an area A roughness element is a surface feature that disturbs the flow of air but is small relative to the size of a pollutant cloud GROUND ROUGHNESS GROUND ROUGHNESS i Open Country Open water Urban or forest B 3 sa t ee A To indicate the ground roughness downwind of a release either a choose one of three roughness classes Open Country low roughness low turbulence Urban or Forest high roughness high turbulence or Open Water very low roughness very low turbulence or b enter your own value for roughness length Z a term used by meteorologists to describe ground roughness e Click Open Country if there are only small or few roughness elements in the area Examples include farmland grassland and large parking lots e Click Urban or Forest if the area has many friction generating roughness elements such as trees or small buildings Examples include residential housing developments industrial areas and forests e Click Open Water if a pollutant cloud is travelling over a large body of water relative to size of the cloud Examples include oceans and large lakes Except when the wind speed is very high Open Water is the lowest ground roughness category in ALOHA Atmospheric Options Wind Speed is 5 C knots mph meters sec Help Wind is from S Enter degrees true or text e g ESE Measurement Height
36. different than this one depending on the display settings you have choosen MARPLOT Prince William County VA DER File Edit View List Objects Sharing Help v Focus Pe JOT aen 113637 v inc ooaj S E Location of workmen Location of release 95 Chapter 3 Examples In this example the chlorine is released at the point where the Norfolk Southern Railway line crosses Lee Highway To indicate this location choose the arrow tool from MARPLOT s tool palette then click once at this intersection MARPLOT will place a visible crosshair mark or click point at this location In MARPLOT s Sharing menu select the ALOHA submenu then click Set Source Point ALOHA s threat zone estimates will automatically be drawn on the map About Sharing Help CAMEOFm b s 1 Set Source Point Set Threat Point r Delete ALOHA Objects Go to ALOHA MARPLOT Prince William County VA File Edit View List Objects Sharing Help CPET G v Fo Note The colors of the threat zones may differ in older versions of MARPLOT 96 Chapter 3 Examples 10 Now you want to estimate the concentration level where the workers were exposed at the intersection of Gallerher Road and Lee Highway Find the intersection this is just outside of the red threat zone Select the arrow tool in the tool palette then click on this location 11 In MARPLOT s Sharing menu select the ALOHA submenu then click Set Thr
37. in the air to sustain a fire or an explosion it is too lean If the fuel air concentration is above the UEL there is not enough oxygen to sustain a fire or an explosion because there is too much fuel it is too rich This is similar to an engine that cannot start because it has been flooded with gasoline If a flash fire occurs the part of the cloud where the fuel air concentration is above the UEL may continue to slowly burn as air mixes with the cloud Is there a difference between a Flammable Limit and an Explosive Limit No there is no difference The two terms can be used interchangeably Some people may prefer to use the terms Lower Flammable Limit LFL and Upper Flammable Limit UFL particularly if they are only concerned with fires You might expect that the LEL could be used as the LOC to determine the areas in which a fire might occur However the concentration levels estimated by ALOHA are time averaged concentrations In an actual vapor cloud there will be areas where the concentration is higher than the average and areas where the concentration is lower than the average This is called concentration patchiness Because of concentration patchiness there will be areas called pockets where the chemical is in the flammable range even though the average concentration has fallen below the LEL ALOHA uses a shorter averaging time when estimating the flammable areas to help compensate for this effect but it cannot completely c
38. inversion height This may cause ground level concentrations of a pollutant to reach higher levels than would otherwise be expected The type of inversion of concern for dispersion modeling is a low level inversion that could trap a pollutant cloud near the ground Sea smoke or low ground fog are good indicators of the presence of this type of inversion A low level inversion is different from the inversion that causes smog That type of inversion is typically thousands of feet above the ground much too high to affect a dispersing gas cloud A jet fire also referred to as a flame jet occurs when a flammable chemical is rapidly released from an opening in a container and immediately catches on fire much like the flame from a blowtorch Thermal radiation is the primary hazard associated with a jet fire Other potential jet fire hazards include smoke toxic byproducts from the fire and secondary fires and explosions in the surrounding area 178 Glossary Level of Concern LOC Liquefied gas Lower Explosive Limit LEL Mass Maximum Average Sustained Release Rate and Maximum Burn Rate A threshold value of a hazard toxicity flammability thermal radiation or overpressure the LOC is usually the value above which a threat to people or property may exist For each LOC you choose ALOHA estimates a threat zone where the hazard is predicted to exceed that LOC at some time after a release begins A gas that has bee
39. its Toxic LOC defaults for the selected chemical To permanently add your own default LOC choose Chemical from the SetUp menu click to highlight the name of the chemical in the list then click Modify In the list of physical properties click Default Level of Concern then type your LOC values in the Default LOC Value 1 2 3 boxes Choose the appropriate units either parts per million or milligrams per cubic meter then click OK For toxic releases there are several hazard classification systems in use Some chemicals have not been classified in every system ALOHA determines its default toxic LOC values based on the following hierarchy of well known LOCs 1 AEGL 2 ERPG 3 TEEL 4 IDLH Note For AEGLs ERPGs and TEELs the rank number increases with the hazard level so that AEGL 3 is more hazardous than AEGL 1 Typically the 3 values are used for the most hazardous red threat zones because they represent the threshold concentration above which health effects may be life threatening Vapor Cloud Explosion Parameters The severity of a vapor cloud explosion depends on many factors including the chemical the cloud size at the time of ignition the type of ignition and the congestion level in the flammable area of the vapor cloud Before ALOHA can generate a threat zone plot for a vapor cloud explosion you must complete the Vapor Cloud Explosion Parameters dialog box Begin by filling in the ignition time The ignition ti
40. level inversion The tank needs to be removed from the tracks and the cargo off loaded The tank has already been subjected to significant stress during the wreck and it is conceivable that it could fail during this effort Possible failure scenarios include e A sudden catastrophic failure leading to a Boiling Liquid Expanding Vapor Explosion BLEVE e A leak leading to a flash fire or a vapor cloud explosion or e A breach leading to a jet of flame from the tank In order to plan a safe response and ensure public safety the potential severity of these threats must be evaluated You will use ALOHA to predict the threat zones for each of these potential scenarios For the last two scenarios you will model the release assuming a seam fails on the tank creating a rectangular hole 40 inches long and 0 1 inch wide Choosing a location and a chemical 1 Start ALOHA In Windows click the Start button point to Programs then choose the ALOHA item On a Macintosh double click the ALOHA program icon located in the ALOHA folder 2 Read the list of ALOHA s limitations click Help to see more details then click OK 3 Select Location from the SiteData menu A Location Information dialog box appears with a list of the names of cities included in ALOHA s location library 66 Chapter 3 Examples 4 The train derails in Columbia South Carolina Type the characters co to quickly move to the section of the list containing names
41. light flag 5 8 11 16 Moderate Raises dust loose paper small branches are moved 8 11 17 21 Fresh Small trees in leaf begin to sway crested wavelets form on inland water 11 14 22 27 Strong Large branches in motion whistling heard in telegraph wires umbrellas used with difficulty 14 17 28 33 Near gale Whole trees in motion inconvenience felt walking against wind 17 21 34 40 Gale Breaks twigs off trees generally impedes progress 114 Chapter 4 Reference Enter the direction from which the wind is blowing using either units of degrees true or one to three letter directional terms For example you can indicate that the wind is blowing from the north northeast by entering either NNE or 22 5 degrees Table 4 3 Wind directions expressed in letter terms and corresponding degrees Directional Letter s Degrees Directional Letter s Degrees N 0 or 360 S 180 NNE 22 5 SSW 202 5 NE 45 SW 225 ENE 67 5 WSW 247 5 E 90 W 270 ESE 112 5 WNW 292 5 SE 135 NW 315 SSE 157 5 NNW 337 5 Finally enter the height at which wind speed and direction have been measured ALOHA accounts for the way in which wind speed changes with height in a pattern called a wind gt profile Close to the ground friction slows the wind At higher elevations the wind speed is faster High enough up typically z TES a few hundred yards or meters or higher th
42. little farther in the downwind direction Notice the role that the direction of the wind plays in both scenarios The toxic threat is confined primarily to the area downwind of the release and even though the thermal radiation threat occurs in all directions it too is shifted downwind from the origin F Toxic Threat Zone gt 1000 ppm ERPG 2 gt 150 ppm ERPG 2 gt 50 ppm ERPG 1 Confidence Lines Scenario Tosg Pool Fire Dispersion Threat Toxicit Thermal Modeled Y radiation Red Threat 82 yards 36 yards Zone Orange Threat 281 yards 51 yards Zone gt 10 0 kW sq m potentially ar within 60 sec Yellow E eter rae Threat 564 yards 78 yards Zone 65 Chapter 3 Examples Example 2 A Tank Source Multiple Scenarios On June 25 2006 at 12 30 p m a train derails in a highly industrialized section of Columbia South Carolina Among the derailed cars is a tank car of propane in a U S Department of Transportation DOT class 112J400W car with a listed capacity of 33 800 gallons The tank is approximately 70 feet long and the tank appears to be intact The propane has been liquefied under pressure At the time of the accident the air temperature is 70 F with the wind from 360 at 10 miles per hour measured at a height of 10 meters by the National Weather Service The sky is completely overcast and the relative humidity is 67 percent There is no low
43. modeled the uncongested vapor cloud explosion you found that a vapor cloud explosion generating a dangerous overpressure is not likely to occur and ALOHA does not display a threat zone plot You also modeled a congested vapor cloud explosion even though you felt the conditions were better described by the uncongested explosion The congested vapor cloud explosion is likely to overestimate the overpressure hazard for your scenario because it does not describe the congestion level in the majority of the cloud The red threat zone for this explosion was not displayed because the chosen LOC was never exceeded Since uncongested is the most accurate congestion level for this scenario you decide that a vapor cloud explosion is not likely to occur However a flash fire could occur regardless of the congestion level so it is important to consider the availability of ignition sources within the flammable area of the vapor cloud A Red Orange Yellow Scenario ANECA one Threat Zone Threat Zone Threat Zone Flammable area Thermal radiation 171 yards No LOC 489 yards if a flash fire occurs selected Vapor cloud explosion Overpressure LOC never LOC never LOC never uncongested exceeded exceeded exceeded Vapor cloud explosion Overpressure LOC never 129 yards 221 yards congested exceeded 81 Chapter 3 Examples Modeling a third scenario jet fire Now that you have considered the flammable area and
44. o ALOHA expects heat to be transferred most readily from default ground or concrete surfaces into a puddle and least readily from sandy ground The heat transfer from water is generally greater than that of any of the other ground types Next indicate the ground temperature which influences the amount of heat transferred between the ground and the puddle The warmer the ground the warmer the puddle and the higher the evaporation rate Type in a value for ground temperature and choose either degrees Fahrenheit or Celsius If you do not know the ground temperature you can choose to estimate that it is about equal to the air temperature In this case click Use air temperature select this if unknown Air and ground temperatures can be very different in some situations such as in a parking lot on a hot day late in the afternoon or on a street during the early morning after a very cold night Be sure to estimate air and ground temperatures carefully in such situations The last piece of information ALOHA needs is the maximum puddle area or diameter If there are no barriers to prevent a puddle from spreading click Unknown For spills on land ALOHA will expect the puddle to spread until it reaches an average depth of 0 5 centimeter about 0 2 inch up to a maximum diameter of 200 meters 220 yards For spills on water ALOHA will expect the puddle to spread until it reaches an average depth of 0 17 centimeter about 0 07 inch Unlike spills
45. of air changes is per hour Select building surroundings Help c ce Select Date amp Time from the SiteData menu A Date and Time Options dialog box appears The release occurs on June 25 2006 at 2 30 p m ALOHA requires time of day in 24 hour time Select the Set a constant time option Type 6 in the Month box 25 in the Day box and 2006 in the Year box Type 14 in the Hour box and 30 in the Minute box click Help to learn how to convert a time value to 24 hour time Click OK Sheltered surroundings trees bushes etc Cancel Unsheltered surroundings Location Ctrl L Building Type Date amp Time Ctrl E Date and Time Options You can either use the computer s internal clock for the model s date and time or set a constant date and time C Use internal clock Seta constant time Input a constant date and time Month Day Year Hour Minute 1 12 1 31 1900 0 23 0 59 Cancel Help 35 Chapter 2 Learning the Basics Choosing a chemical As you build your ALOHA scenario your next Atmospheric bs task is to choose the chemical that is being Source gt released chlorine Calculation Options 1 To choose chlorine select Chemical from the SetUp menu A Chemical Chemical Information Information dialog box appears with alist y Pure Chemicals of the chemicals in ALOHA s chemical C Solutions ETA library CARBON TETRAFLUORIDE a EEN
46. older version of MARPLOT the orange threat zone will be displayed as a green threat zone by default Go to ALOHA e Set Threat Point First click the location on your MARPLOT map for which you wish to see threat information Next choose Set Threat Point to tell ALOHA the location ALOHA will place a symbol at that location then come forward to make concentration calculations and display the Threat at Point plot ALOHA will use fixed east west north south coordinates to remember the point s position e Delete ALOHA Objects Choose this item to remove all objects placed on the map by ALOHA ALOHA then will no longer update the map every time it generates new information e Goto ALOHA Choose this item to bring ALOHA forward MARPLOT Prince William County VA File Edit View List Objects Sharing Help Threat Point ie Confidence Line 161 Chapter 4 Reference 162 Troubleshooting Often when you encounter difficulties while running ALOHA it will alert you of the problem and suggest a solution At other times you may encounter a problem and not know how to solve it Below are some of these cases For more ALOHA information check the ALOHA Web site at http response restoration noaa gov aloha In the Text Summary I see tank volume estimated to be 5 2e8 gallons How many gallons is that ALOHA gave me an outdoor concentration estimate that s greater than 1 million parts per million how can that be
47. on land there is no maximum diameter for spills on water If there is a barrier to liquid flow such as a containment or diked area then type the approximate diameter of the barrier or area that it encloses Select appropriate units and click OK If an unpressurized liquid leaks from a tank and forms a burning puddle you only need to enter the Maximum Puddle Size Input maximum puddle diameter or area Help maximum puddle area or diameter because ground type and ground temperature do not affect pool fire calculations Note ALOHA does not model pool fires on water Unknown Maximum diameter C Maximum area G ft C yds C meters Cancel is 145 Chapter 4 Reference Gas Pipeline In the SetUp menu point to Source then select Gas Pipeline Choose the Gas Pipeline source option to model the release of a gas from a leaking gas pipeline If the chemical is flammable the release can be modeled as a jet fire as well Chemical Ctrl H Atmospheric Source gt Calculation Options Direct Ctrl D Puddle Ctrl U Tank Ctrl T Gas Pipeline Ctrl I You can use ALOHA to model two types of gas pipeline leak scenarios A pipeline connected to a very large infinite reservoir so that gas escapes from the broken end of the pipeline at a constant rate for an indefinite period of time or A finite length of pipeline that is closed off at the unbroken end for example by a shut off valve Because t
48. other information in a text summary and on a source strength graph Gas Pipeline Ctrl I Note ALOHA does not display a source strength graph for BLEVE scenarios ALOHA s duration limits ALOHA places minimum and maximum limits on the duration of any release ALOHA expects a release into the atmosphere to continue for at least 1 minute If ALOHA calculates a source strength evaporation rate or burn rate for your current scenario it estimates it for no more than 1 hour after a release begins If ALOHA predicts that a release would last longer than 1 hour you will see a message on the Text Summary window Release Duration ALOHA limited the duration to 1 hour One important reason for the 1 hour duration limit is that the wind changes speed and switches direction frequently Researchers have found that atmospheric conditions change enough to affect ALOHA s predictions on a time scale of about 1 hour Bear in mind that ALOHA assumes that weather conditions remain constant for the duration of any release Another reason is that the calculation methods ALOHA uses are based on the results of experiments In these experiments gases were released into the atmosphere for time periods from 10 minutes to 1 hour the researchers then observed how the dispersing gases behaved This 1 hour limit represents the maximum possible release duration If you are responding to an incident check whether release conditions change substantially before an hour h
49. rate during the hour after the release begins F Source Strength Release Rate pounds minute 20 minutes On the graph time since the release started from 0 to 40 minutes is shown on the horizontal axis minutes and release rate is shown on the vertical axis pounds minute You can see from this graph that because the chlorine is escaping from a pressurized container ALOHA predicts that release rate starts out high then declines as container pressure drops The highest step on this graph is the Maximum Averaged Sustained Release Rate 40 Chapter 2 Learning the Basics In the Text Summary under the Source Strength heading you can see the estimated Maximum Average Sustained Release Rate ALOHA predicts release rate from a puddle tank or gas pipeline as a series of hundreds of brief timesteps ALOHA then averages this series of many release rates into between one and five release rates each averaged over a time period of at least 1 minute The Maximum Average Sustained Release Rate is the highest of these averaged release rates To save calculation time ALOHA uses only the averaged release rate s to make its threat zone estimates Text Summary SITE DATA Location SIOUX FALLS SOUTH DAKOTA Building Air Exchanges Per Hour 6 43 unsheltered single storied Time June 25 2066 1436 hours CDT user specified CHEMICAL DATA Chemical Name CHLORINE Molecular Weight 76 91 g mol AEGL 1 66 min 6 5 ppm AEGL 2 6
50. selected Click OK A Liquid Mass or Volume dialog box appears Chemical State and Temperature Enter state of the chemical Tank contains liquid Tank contains gas only C Unknown Enter the temperature within the tank Chemical stored at ambient temperature C Chemical stored at 80 degrees Cancel 53 Chapter 3 Examples 4 The security guard thinks the 500 gallon tank was filled that evening so the most conservative estimate you can make is that the tank is 100 percent full Either 1 type 100 in the full by volume box 2 type 500 in the liquid volume box then click gallons or 3 scroll the liquid level bar to the top of the tank diagram Notice that ALOHA fills in the other values Click OK A Type of Tank Failure dialog box appears Liquid Mass or Volume Enter the mass in the tank OR volume of the liquid C pounds The mass in the tankis 1 82 tons 2 000 Ibs C kilograms OR Enter liquid level OR volume gallons rE Ms ee C cubic feet volume is 500 C liters C cubic meters 100 full by volume l Cancel Help 5 Initially the benzene is leaking from a hole in the tank but it is not burning Choose the Leaking tank chemical is not burning and forms an evaporating puddle option Click OK An Area and Type of Leak dialog box appears Type of Tank Failure Scenario Tank containing an unpressurized flammable liquid Type of Tank Failure Leaking tank chemi
51. speed in miles per hour an English unit you will see wind speed displayed in those units on the Text Summary screen even if you selected metric output units 158 Chapter 4 Reference Sharing menu The programs that make up the CAMEO Computer Aided Management of Emergency Operations package work together by means of the Sharing menu Any application that can communicate with ALOHA can install a menu under ALOHA s Sharing menu A menu installed by another application into the ALOHA Sharing menu belongs to the installing application Both CAMEO and MARPLOT automatically install menus under ALOHA s Sharing menu ALOHA automatically saves menus that other applications have placed in its Sharing menu When you use a saved menu that belongs to an application that is not currently running ALOHA will start that application so that it can carry out the specified action You can delete a menu from the Sharing menu if you wish you might want to do so if you remove an application from your hard drive To do this choose Edit Shared Menus from the Sharing menu select the menu that you wish to delete then click Delete Items in the Sharing menu Two items always appear in the Sharing menu whether or not ALOHA is sharing information with another program e Choose About Shared Menus to view on screen help information about information sharing between ALOHA and other programs e Choose Edit Shared Menus to delete an application s menu fro
52. the Text Summary screen or paste it into a word processing document You ll need the information to compare the scenarios later 79 Chapter 3 Examples 10 Choose Threat Zone from the Display menu The Hazard To Analyze dialog box appears again 11 Blast Area of Vapor Cloud Explosion is already selected so click OK The Vapor Cloud Explosion Parameters dialog box appears again 12 Keep you previous settings for ignition time and ignition type but choose congested as the congestion level Click OK The Overpressure Level of Concern dialog box appears again 13 Keep ALOHA s default LOCs and check that Show confidence lines only for the longest threat zone has been selected Click OK ALOHA will display a threat zone plot for this release ALOHA s threat zone window appears ALOHA has plotted the orange and yellow threat zones A review of the Text Summary reveals that the red threat zone was not plotted because the LOC was never exceeded and that the orange threat zone is predicted to extend 129 yards in the downwind direction Note that because you chose the unknown time option ALOHA ran explosion scenarios for a range of ignition times encompassing all of the possible ignition times for your scenario Therefore these threat zones do not represent the blast area from a single explosion but rather the composite of potential blast areas for all of the different ignition time scenarios that ALOHA ran F Overpressure Blast Forc
53. the severity of a vapor cloud explosion Congestion refers to the density of obstacles that generate turbulence Obstacles of this nature are generally small like a shrub and do not impede the flame front Larger objects like a building can impede the flame front so they should not be considered obstacles for the purposes of congestion Greater turbulence allows the flame front to accelerate thereby generating a more powerful blast wave i e greater overpressure ALOHA uses two congestion levels congested and uncongested An estimate that is more likely to result in threat zone and hazard estimates that are too large rather than too small Selecting conservative choices for weather conditions low wind speed and a stable atmosphere source strength larger puddle area or higher release rate or LOC a small LOC results in a larger threat zone A source that releases gas into the atmosphere at a constant or near constant rate for an extended period of time Perpendicular to the wind Relating to processing or storing substances at very low temperatures For purposes of ALOHA the use and storage of gases liquefied by refrigeration 172 Glossary Daylight savings time Deflagration explosion Density Detonation explosion DIPPR data Direct source Dispersion At most U S locations daylight savings time is put into effect each spring when local standard time is advanced by 1 hour the time is moved back
54. then click Delete Click OK to delete the chemical permanently from ALOHA s library Click Cancel to avoid deleting the chemical Atmospheric You can enter information about current weather conditions into ALOHA either manually by typing in values for wind speed air temperature and other weather factors or by connecting your computer to a portable meteorological station called a SAM Station for Atmospheric Measurement ALOHA uses the information that you enter to account for the main processes that affect the results of the various scenarios These include atmospheric heating and mechanical stirring low level inversions wind speed and direction ground roughness and air temperature User Input In the SetUp menu point to Atmospheric then select User Input The first of two Atmospheric Options dialog boxes appears In the dialog boxes manually enter the following information about conditions in the vicinity of an accidental release wind speed and direction wind measurement height ground roughness cloud cover air temperature atmospheric stability class inversion height if a low level inversion exists and relative humidity Chemical Ctrl H Source gt SAM Station Calculation Options ALOHA assumes that weather conditions remain constant throughout the incident area For this reason use values that best represent conditions throughout this area If weather conditions change update this information and run ALOHA ag
55. through the flammable vapor cloud igniting areas where the concentration is in the flammable range The explosion produces a pressure wave that spreads out into the surrounding area causing damage to people and property The greater the speed of the flame front the more intense the pressure wave overpressure and the greater the destructive force of the explosion For most accidental explosions the flame front will travel relatively slowly in what is called a deflagration For example a typical deflagration flame front for hydrocarbon combustions travels about 2 2 miles per hour or 1 meter per second Lees 2001 For intentional explosions and worst case accidental explosions the flame front travels rapidly in what is called a detonation For example a typical detonation flame front for hydrocarbon combustions travels about 5 600 miles per hour or 2 500 meters per second Lees 2001 In some situations a deflagration flame front can accelerate into a detonation flame front Accidental explosions that result in a high speed deflagration or a detonation are more likely to occur in areas of high congestion and confinement Congestion and confinement Congestion is a concept used to quantify the way small structures within the vapor cloud affect the severity of the explosion Congestion refers to the density of obstacles that generate turbulence Obstacles of this nature are generally small like a shrub and do not impede the flame front La
56. to rerun a scenario in the future If you modified property information about a selected chemical while setting up a scenario you can save this information in a saved file without making a permanent change to the chemical library When you open and use a saved file in ALOHA in planning mode all the information in the file will be restored When you open and use a saved file in ALOHA in response mode you ll still need to enter information specific to a particular release such as weather conditions and the amount of material released before you can obtain a source strength estimate or threat zone plot Print Print All and Print or Page Setup Choose Print to print the contents of the front ALOHA window Choose Print All to print the contents of all active ALOHA windows Choose Print Setup in Windows or Page Setup on a Macintosh to choose the printer and other print options Quit or Exit Choose Quit on a Macintosh or Exit in Windows to exit ALOHA To save the scenario you have been working with select Save or Save As from the File menu before exiting from the program Edit menu Copy Choose Copy to copy pictures or selected text from the front window to the clipboard You can then paste copied items into a Copy Ctrl C word processing or graphics application The Undo Cut Paste and Clear menu items are not available in ALOHA 100 Chapter 4 Reference SiteData menu The SiteData menu is the first menu in ALOH
57. upwards and outwards as they are transported ae mnenj downwind and are reflected from an 3 Ia inversion layer back towards the ground A Penn z soe ae o heavy gas cloud in contrast remains close to the ground as it disperses and is not normally Cancel affected even by low level inversions If a low level inversion is present type in the height of the inversion layer and select units If there is no low level inversion be sure that No Inversion is selected Humidity Relative humidity is the ratio of the amount of water vapor that the air contains to the maximum amount of water vapor that the air could hold at the ambient temperature and pressure Relative humidity is expressed as a percentage When relative humidity is 50 percent the air contains one half as much water vapor as it could potentially hold The warmer the air the greater its capacity to contain water vapor Cold air may contain little water vapor but have a high relative humidity because the amount of water vapor in the air is near the air s relatively low maximum capacity ALOHA uses the relative humidity value to e Estimate the atmospheric transmissivity value e Estimate the rate of evaporation from a puddle and e Make heavy gas dispersion computations Atmospheric transmissivity is a measure of how much thermal radiation from a fire is absorbed and scattered by the water vapor and other atmospheric components ALOHA estimates the transmissivity from relative hu
58. was spilled that is the amount of water in the soil Cancel 135 Chapter 4 Reference ALOHA expects heat to be transferred most readily from default ground or concrete surfaces into a puddle and least readily from sandy ground The heat transfer from water is generally greater than that of any of the other ground types Next indicate the ground temperature which influences the amount of heat transferred between the ground and the puddle The warmer the ground the warmer the puddle and the higher the evaporation rate Type in a value for ground temperature and choose either degrees Fahrenheit or Celsius If you do not know the ground temperature you can choose to estimate that it is about equal to the air temperature In this case click Use air temperature select this if unknown Air and ground temperatures can be very different in some situations such as in a parking lot on a hot day late in the afternoon or on a street during the early morning after a very cold night Be sure to estimate air and ground temperatures carefully in such situations The last piece of information ALOHA needs is the initial puddle temperature ALOHA assumes the initial temperature to be the same throughout the depth and width of the puddle Indicate that the initial puddle temperature equals either the ground temperature or the ambient air temperature or enter a value for the initial puddle temperature Click the button that represents your ch
59. 0 Check to be sure that No Inversion is selected Cancel 9 The relative humidity is about 80 percent Type 80 in the humidity value box Click OK The information that you have entered into ALOHA appears in the Text Summary Review the Text Summary to be sure you have entered all of the data correctly Text Summary SITE DATA Location MANASSAS VIRGINIA Building Air Exchanges Per Hour 6 58 unsheltered single storied Time June 4 2666 1566 hours EDT user specified CHEMICAL DATA Chemical Name CHLORINE Molecular Weight 76 91 g mol AEGL 1 66 min 6 5 ppm AEGL 2 66 min 2 ppm AEGL 3 66 min 26 ppm IDLH 16 ppm Carcinogenic risk see CAMEO Ambient Boiling Point 29 5 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 666 ppm or 166 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 6 miles hour from E at 3 meters Ground Roughness open country Cloud Cover 3 tenths Air Temperature 72 F Stability Class C No Inversion Height Relative Humidity 86 Describing the release Now you re ready to enter information about the release itself that is to set the source for this release This is a release from three cylindrical tanks but you don t have all the information that you would need to model the release with ALOHA s Tank source option You can model this release as a Direct source however 1 Inthe SetUp menu point to Source then select Direct
60. 1 hour in the fall to become standard time again When you select a U S location ALOHA automatically switches between standard to daylight savings time for you when necessary depending on the date that you enter You must manually make this switch for locations outside the U S Rapid sharp combustion with sudden evolution of flame The flame front travels relatively slowly subsonic speeds as compared to a supersonic detonation The ratio of the mass weight of a substance to the volume it occupies For example if 1 cubic foot of a substance weighs 10 pounds its density is 10 pounds per cubic foot An explosion where the flame front travels at supersonic speeds as a shock wave Explosions of this nature are often triggered by a high power explosive device Typically detonation explosions are significantly more damaging than deflagration explosions Values for physical properties compiled by the Department of Chemical Engineering of Brigham Young University for the Design Institute for Physical Property Data DIPPR of the American Institute of Chemical Engineers These values are included in ALOHA s chemical library for more than half of the chemicals in the library DIPPR Web site http dippr byu edu Choose this source option when you know or can estimate either the amount of pollutant gas entering the atmosphere or its rate of entry i e evaporation rate For ALOHA s purposes the process by which a cloud of pollutant
61. 186 heavy gas 17 Tank source 137 U uncertainty lines See confidence lines uncongested 27 unsheltered surroundings 105 Upper Explosive Limit UEL 19 26 Upper Flammable Limit UFL 26 urban or forest ground roughness 116 User Input menu item 113 121 y vapor cloud explosion congestion level 151 deflagration and detonation 27 explanation of 26 ignited by detonation 151 ignition time 150 ignition type 151 threat zone 150 ventilation systems 105 volatility 19 volume blockage ratio 27 W wind direction 115 eddies 174 estimating speed 114 measurement height 115 one hour duration 30 profile 115 stability class 120 terrain steering 29 very low speeds 28 Wind Rose menu item 127 Index Z Zo roughness length 117 195
62. 31 yards Flammable area Thermal radiation 171 yards No LOC 489 yards if a flash fire occurs selected Vapor cloud explosion Overpressure LOC never LOC never LOC never uncongested exceeded exceeded exceeded Vapor cloud explosion Overpressure LOC never 129 yards 221 yards congested exceeded Jet fire Thermal radiation 58 yards 83 yards 129 yards 84 Chapter 3 Examples Example 3 A Direct Source and a MARPLOT Map At 3 p m on June 4 2006 a train traveling on the Southern Railway near Manassas Virginia collides with a Stalled truck at Lee Highway Three 150 pound chlorine cylinders that were in the truck bed are damaged during the collision and simultaneously release their contents At the time of the release winds are out of the east at about 6 miles per hour measured at a height of 3 meters One third of the sky is covered by clouds the humidity is about 80 and the air temperature is 72 F There is no low level inversion The land between the accident site and the intersection of Gallerher Road with Lee Highway is flat with no obstructions Two workmen repairing potholes at this intersection are overcome by fumes and treated at a local hospital for chlorine gas inhalation To what approximate concentration of chlorine might the workmen have been exposed You ll evaluate this scenario first by using ALOHA to obtain a source strength estimate and a threat zone plot and then by displaying the threat zones on a MARPLOT m
63. 6 gallons Tank contains liquid Internal Temperature 72 F Chemical Mass in Tank 1 tons Tank is 68 full Circular Opening Diameter 6 5 inches Opening is 1 25 feet from tank bottom Release Duration 33 minutes Max Average Sustained Release Rate 172 pounds min averaged over a minute or more Total Amount Released 827 pounds Note The chemical escaped as a mixture of gas and aerosol two phase flow THREAT ZONE Model Run Heavy Gas Red 1124 yards 20 ppm AEGL 3 66 min Orange 1 7 miles 2 ppm AEGL 2 66 min Yellow 2 8 miles 6 5 ppm AEGL 1 66 min THREAT AT POINT Concentration Estimates at the point Downwind 1566 yards Off Centerline 6 yards Max Concentration Outdoor 16 9 ppm Indoor 6 342 ppm Exiting Quitting ALOHA When you ve completed your work with ALOHA just choose Exit from the File menu if you re using Windows or Quit from the File menu if you re using a Macintosh You can also first save any ALOHA scenario as a file you can reopen later in ALOHA see Save and Save As on page 100 48 Examples This chapter contains three step by step ALOHA example scenarios You can complete the first two scenarios using only ALOHA To complete the third scenario you ll also need the electronic mapping application MARPLOT as well as the sample map of Prince William County supplied with MARPLOT Example 1 A Tank Source Puddle and Pool Fire In a small industrial park outside Baton Ro
64. 6 min 2 ppm AEGL 3 66 min 26 ppm IDLH 16 ppm Carcinogenic risk see CAMEO Ambient Boiling Point 31 2 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 666 ppm or 166 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 5 miles hour from S at 16 meters Ground Roughness open country Cloud Cover 3 tenths Air Temperature 72 F Stability Class B No Inversion Height Relative Humidity 56 SOURCE STRENGTH Leak from short pipe or valve in horizontal cylindrical tank Non flammable chemical is escaping from tank Tank Diameter 2 5 feet Tank Length 6 8 feet Tank Volume 256 gallons Tank contains liquid Internal Temperature 72 F Chemical Mass in Tank 1 tons Tank is 68 full Circular Opening Diameter 6 5 inches Opening is 1 25 feet from tank bottom Release Duration 33 minutes Max Average Sustained Release Rate 172 pounds min averaged over a minute or more Total Amount Released 827 pounds Note The chemical escaped as a mixture of gas and aerosol two phase flow The Text Summary window is like a blackboard you can check its contents at any time to verify that you ve entered correct values into ALOHA or to review ALOHA s results If your Text Summary window doesn t look like the one above revise any incorrect information by choosing the appropriate menu item then modifying the information that you entered For example if you indicated that the building is sheltered rather t
65. 7 feet Tank Length 76 feet Tank Volume 33866 gallons Tank contains liquid Internal Temperature 76 F Chemical Mass in Tank 76 1 tons Tank is 166 full Opening Length 46 inches Opening Width 6 1 inches Opening is 6 feet from tank bottom Release Duration 26 minutes Max Average Sustained Release Rate 5 736 pounds min averaged over a minute or more Total Amount Released 146 266 pounds Note The chemical escaped as a mixture of gas and aerosol two phase flow Choosing LOCs and creating threat zone plots for a flammable vapor cloud 1 Choose Threat Zone from the Display menu A Hazard To Analyze dialog box appears 2 ALOHA can help you model three possible hazardous scenarios for the flammable vapor cloud toxic area flammable area or blast area For this example first you want to display the flammable area of the vapor cloud on a threat zone plot The flammable area is the predicted area where the ground level vapor fuel concentration in air is within the flammable range and can be ignited Then you will use the threat zone plot to determine possible ignition sources and the level of congestion within the vapor cloud both of which affect whether a vapor cloud explosion is possible Select the Flammable Area of Vapor Cloud option A Flammable Level of Concern dialog box appears Hazard To Analyze Scenario Flammable chemical escaping from tank Chemical is NOT on fire Choose Hazard to Analyze C Toxic Area of Vapor Clo
66. 7 percent Type 67 in the humidity value box Click OK The information that you have entered into ALOHA appears in the Text Summary Ignore ALOHA s estimate of building exchange rate since you are not considering infiltration into buildings Text Summary SITE DATA Location COLUMBIA SOUTH CAROLINA Building Air Exchanges Per Hour 6 52 unsheltered single storied Time June 25 26066 1236 hours EDT user specified CHEMICAL DATA Chemical Name PROPANE Molecular Weight 44 16 g mol TEEL 1 2166 ppm TEEL 2 2166 ppm TEEL 3 2166 ppm IDLH 2166 ppm LEL 26666 ppm UEL 95666 ppm Ambient Boiling Point 44 6 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 666 ppm or 160 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 16 miles hour from 366 true at 16 meters Ground Roughness urban or forest Cloud Cover 16 tenths Air Temperature 76 F Stability Class D No Inversion Height Relative Humidity 67 69 Chapter 3 Examples Describing the release Now you re ready to enter information about the release itself that is to set the source for this release You ll begin by modeling the BLEVE scenario 1 The propane might leak from a tank car In the SetUp menu point to Source then select Tank A Tank Size and Orientation dialog box appears 2 The propane is stored in a 33 800 gallon 70 foot long horizontal tank car Select horizontal cylinder Type 33
67. 800 in the volume box then select gallons Type 70 in the length box then select feet Notice that ALOHA automatically calculates the tank diameter Click OK A Chemical State and Temperature dialog box appears Tank Size and Orientation Select tank type and orientation Vertical cylinder Horizontal cylinder c Enter two of three values diameter 9 07 length 70 volume 33800 gallons C cu feet Cancel Help feet C meters diameter 3 The propane is stored in the tank as a liquid the propane was liquefied by pressure not by refrigeration Select the Tank contains liquid option Check to be sure that Chemical stored at ambient temperature is selected Click OK A Liquid Mass or Volume dialog box appears Chemical State and Temperature Enter state of the chemical Tank contains liquid C Tank contains gas only C Unknown Enter the temperature within the tank Chemical stored at ambient temperature C Chemical stored at 70 degrees Cancel 70 Chapter 3 Examples 4 You are not sure how full the tank is but you want to make a worst case estimate so you will assume the tank is filled to capacity 33 800 gallons Either 1 type 100 in the full by volume box 2 type 33800 in the liquid volume box then click gallons or 3 scroll the liquid level bar to the top of the tank diagram Notice that ALOHA fills in the other values Click OK A Type of Tank Failure dialog box app
68. A Direct Source dialog box appears 88 Chapter 3 Examples 2 Three 150 pound chlorine cylinders that were in the truck bed are damaged during the collision and simultaneously release their contents Select pounds as your units of source strength This is an instantaneous release so select Instantaneous source Because the chlorine is released simultaneously you can model the release from all three tanks as a single release Type 450 into the amount box The truck bed is roughly at ground level so type 0 in the source height box Click OK Direct Source Select source strength units of mass or volume Help C grams C kilograms pounds C tons 2 000 Ibs C cubic meters liters C cubic feet C gallons Select an instantaneous or continuous source Instantaneous source C Continuous source Enter the amount of pollutant ENTERING THE ATMOSPHERE Help 450 pounds Enter source height feet 0 if ground source 0 C meters 3 ALOHA will alert you that the chemical may flash boil and or escape as a two phase flow i Note This chemical may flash boil and or result in two phase flow Click Help to view background information about flash boiling and two phase flow ALOHA recognizes that because the boiling point of chlorine is well below air temperature the chlorine may have been stored as a liquefied gas If so it may flash boil when released through a hole in a tank During flash boiling much o
69. A E lial aes EEES ea gedaleloen 128 ALOHA S d raton ATU yas cian sliea ees oan ease asa ca saga 129 ALOHA reports release rate cass cascccacacs yeossskcbgunesapdnneeassGesencbovages aadeansoeann ee 130 When you re using a SAMs i s sccassscccsassdcpacatendecesanecedanabedsnecaaszccceesscsennteys 130 Table of Contents Direct SOUTCE xan Sie toe reesei ea BA Glad ean el eta 130 Direct release of gas into the atmosphere eee eeeeesecsneceeeeeeeeeeneees 131 Source height sci s5 secesacasvoraddisssvedenspessdeasessaccensnessannaponacddacavedeasperssvelwosacensya 132 PUT SS OC ccs cece neste E a eat EEE ER EERE 132 Type of PU eros apt tes fet aac nM nea ae cnt iit ee Bi ace regis 133 Evaporatin Puddles cc ccccsssvsssactunvasceaasesiaccasstcvevsdevcaacsety a 133 Ar a a d V OlUIG 232i wi Reda achte Ba et Sede Sa ete sce Bk ea cde 135 Ground Type and Initial Temperatures ee eeeceeseceeeceeeeeeaeeenneees 135 DANA E E 136 Liguefied Sases nite Behn ee eee eee 137 Tank Size and Orientation e221 edie Noes esses cepetes tsetse Mea fae 138 Chemical State and Temperature c i cssccasecccesesedeedeasvescadeendcansesesteceens 138 Jeiquind na tank oranini Le See She 139 G s ina t nk ocne iinn ee pee E Ee ce erty Satire mre nd Ne ene ae 140 Chemical of unknown state in a tank eee ceeeeereecneeceeeeeeeeeeaeeenaeens 140 Type of Wank Patlitees sree ee e E e Ea Ei 141 Percent Mass 10 Fireball einioes riietati aiina at 142 Area and Ty
70. A that you use to enter information about a release scenario Use the three items in this menu to enter information about e The geographic location of the chemical release e The type of buildings in the area downwind of a toxic siteData chemical release and Location Ctrl L Building Type e The date and time of the release Date amp Time Ctrl E Location Choose this item to specify the geographical location of a release ALOHA uses the latitude longitude elevation and time zone of the location of a chemical release in some of its computations This information for many cities and towns where ALOHA users reside is already included in ALOHA s location library CityLib You can add descriptions of other locations ALOHA uses location information to estimate e Sun angle ALOHA uses latitude longitude and time of day for this calculation and e Atmospheric pressure determined by the location s elevation The angle of the sun is important when a chemical has formed a puddle on the ground that is evaporating ALOHA calculates the amount of energy coming into the puddle from the atmosphere and from the ground For example if the sun is high in the sky around noon the amount of energy coming into the puddle is greater than it would be in the early morning or late afternoon when the sun is lower The more energy coming in the higher the evaporation rate Selecting a location To specify the location where a release is
71. Gas Pipeline chemical is escaping from a ruptured gas pipeline For each source ALOHA will allow you to choose the scenario s you wish to model The number of available scenarios depends on the source and the chemical released Table 4 8 lists the scenarios that ALOHA can model for each source Table 4 8 ALOHA sources and scenarios Source Toxic Scenarios Fire Scenarios Explosion Scenarios Direct Direct Release Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Puddle Evaporating Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Pool Fire Pool Fire Tank Not Burning Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Jet Fire or Pool Fire BLEVE BLEVE Fireball and Pool Fire Gas Pipeline Not Burning Toxic Vapor Cloud Flammable Area Flash Fire Vapor Cloud Explosion Burning Jet Fire Jet Fire 128 Chapter 4 Reference When you choose one of the four source SetUp options from the SetUp menu you will need Chemical Cirith to enter information about the release on a ve Atmospheric gt series of dialog boxes Once you click OK on Direct Ctrl D the last dialog box ALOHA will make its Puddle Sri source strength calculations and you ll be Calculation Options Tank T Ctrl T able to review the results of the source calculations predicted release duration release rates total amount released and
72. IMEE EENE X 2 You want to know the thermal radiation threat for the pool fire Keep ALOHA s default LOCs Orange Ties Zale and ciek OK ALOHA will tc display a threat zone plot for Yellow Threat Zone this release Loc 2 0 k Wi sq m pain within 60 sec m Cancel 63 Chapter 3 Examples You ll see ALOHA s threat zone plot for this scenario showing three nearly circular thermal radiation threat zones The red threat zone represents the worst hazard level and the orange and yellow threat zones represent areas of decreasing hazard Unlike the toxic threat the thermal radiation threat extends in all directions simultaneously But it extends a little farther in the downwind direction For example ALOHA estimates that the orange threat zone will extend 51 yards in the downwind direction This threat distance is shown in the Text Summary The orange threat zone extends only about 40 yards in the upwind direction This difference exists because the wind tilts the flames in the downwind direction leading to a greater thermal radiation threat in that direction It is important to realize that there may be additional hazards that are not modeled by ALOHA including secondary fires and explosions Thermal Radiation Threat Zone 50 o 50 yards gt 10 0 kW sq m potentially lethal within 60 sec gt 5 0 kW sq m 2nd degree burns within 60 sec co gt 2 0 kW sq m pain within 60 sec Check
73. OHA only models the toxic threat specifically how a toxic gas cloud might disperse in the atmosphere after an accidental chemical release ALOHA runs quickly on small computers Microsoft Windows or Macintosh that are easily transportable It is designed to be easy to use so that you can operate it successfully during high pressure situations Its chemical library contains information about the physical properties of approximately 1 000 common hazardous chemicals Its computations represent a compromise between accuracy and speed ALOHA has been designed to produce good results quickly enough to be of use to responders ALOHA is designed to minimize operator error It checks information that you enter and warns you when you make a mistake ALOHA s on screen help offers you quick access to explanations of ALOHA s features and computations as well as background information to help you interpret its output ALOHA was developed jointly by the National Oceanic and Atmospheric Administration NOAA and the Environmental Protection Agency EPA Basic program organization To use ALOHA you ll typically perform several basic steps 1 Indicate the city where a chemical release is occurring and the date and time 2 Choose the chemical of concern from ALOHA s library of chemical information 3 Enter information about current weather conditions 4 Describe how the chemical is escaping from containment and 11 Chapter 1 Welcome to ALOHA
74. SAM it will display an error message in this window Several items in the Processed SAM Data window need Processed Sam Data explanation leteorological Station ID 999 e The Meteorological Station ID is the identification code of the SAM that is sending data to your computer this ID is BN gs pals oa assigned by the manufacturer Temperature e Wind Direction in the case of both instantaneous and catia ean average values is the direction from which the wind is Wind Speed Wind Direction j Temperature blowing Sigma Theta e The standard deviation of the wind direction is called Sigma Battery Voltage Theta This value reflects the amount of fluctuation in the wind direction during the last 5 minutes The more the wind switches direction the larger is the value of sigma theta INSTANTANEOUS 26 2 mph 229 degrees true 73 Fahrenheit AVERAGE 26 1 mph 218 degrees true 73 Fahrenheit 8 1 degrees 12 36 volts ALOHA uses sigma theta along with wind speed cloud cover and time and date to choose the stability class for your scenario The SAM transmits a value of 1 00 for sigma theta until it has been transmitting for 5 minutes e Battery Voltage is the remaining voltage of the battery on your SAM 126 Chapter 4 Reference Wind Rose Choose Wind Rose from the SAM Options menu to view a diagram showing the 10 most recent average wind speed and direction values received from the SAM station
75. T ZONE Threat Modeled Flammable Area of Vapor Cloud Model Run Heavy Gas Red 171 yards 12 066 ppm 66 LEL Flame Pockets Yellow 489 yards 2 606 ppm 16 LEL 4 Either print out the threat zone plot and the Text Summary screen or paste them into a word processing document You ll need the information to compare the scenarios later Now that you know where the estimated flammable portion of the cloud is you can identify possible ignition sources and the level of congestion within that area to model a vapor cloud explosion The portion of the cloud that might participate in a vapor cloud explosion the red zone on the threat zone plot is expected to travel through a slightly congested area where there are many likely ignition sources e g mechanical sparks 5 Choose Threat Zone from the Display menu The Hazard To Vapor Cloud Explosion Parameters Analyze dialog box appears again Time of vapor cloud ignition Help This time choose Blast Area of unknown show composite threat zone from all possible ignition times Vapor Cloud Explosion Click OK known Ignition time is A Vapor Cloud Explosion Parameters dialog box appears 6 You do not know the ignition time so TYP of vapor cloud ignition Help select unknown show composite ignited by spark or flame threat zone from all possible eae ay detonation ignition times Because the flammable area of the vapor cloud is EE ERE of the vapor cloud heip
76. The CAMEO Software System ALOHA USER S MANUAL February 2007 U S ENVIRONMENTAL PROTECTION AGENCY Office of Emergency Management Washington D C NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Office of Response and Restoration Emergency Response Division Seattle Washington pO ATMOS Phy lt D QA y Ba rs SS en erent oF 29 Terms and Conditions for ALOHA The recipient of the ALOHA software and documentation agrees to the following guidelines and restrictions Use and Distribution Restrictions ALOHA is available at no charge to those organizations and individuals recipients responsible for the safe handling of chemicals Certain physical property data and equation coefficients contained in ALOHA have been supplied by and are the property of the Design Institute for Physical Properties DIPPR DIPPR data shall not be duplicated by the recipient without written permission from DIPPR Additionally ALOHA contains other copyrighted information including ERPGs published by the American Industrial Hygiene Association and AEGLs published by the National Advisory Committee for AEGLs The recipient shall honor all disclaimers and other limits of liability associated with those organizations that have provided data in the compilation of the ALOHA chemical database Limitation of Liability The United States Government has used its best efforts to incorporate accurate and complete data into ALOHA
77. The liquid benzene is flowing onto a paved area in the industrial park Select the Concrete ground type Since you have no information about the ground temperature select Use air temperature select this if unknown Because the product is flowing onto a paved area it is probably not contained by a dike so it will continue spreading outward until it reaches a minimum thickness Under the Input maximum puddle diameter or area heading click Unknown ALOHA will calculate the area for you based on the release information you provided up to a maximum diameter of 200 meters Click OK Text Summary SOURCE STRENGTH Leak from hole in vertical cylindrical tank Puddle Parameters Help Select ground type C Default soil select this if unknown Concrete Moist sandy soil G C Sandy dry soil A C Water Input ground temperature Help Use air temperature select this if unknown C Ground temperature is 80 deg CF OC Input maximum puddle diameter or area Help Unknown C Maximum diameter C Maximum area ft C yds C meters Cancel is Ha The source strength information that you have entered and the results of ALOHA s source strength calculations appear in the Text Summary ALOHA estimates that the release of vapor into the atmosphere lasts for about 46 minutes and that the maximum amount of vapor released at any one time is 77 2 pounds per minute this is the Maximum Average Sustained Release Rate ALOHA es
78. a significant amount of the chemical flash boils ALOHA assumes that any liquid not consumed in the fireball will form a pool fire ALOHA estimates the thermal radiation hazard from a fireball and or a pool fire Other potential BLEVE hazards include overpressure hazardous fragments smoke and toxic byproducts from the fire although ALOHA does not model these hazards ALOHA focuses on the thermal radiation because in most BLEVEs thermal radiation impacts a greater area than the overpressure and is the more significant threat Fireball When you model a BLEVE ALOHA assumes that a fireball will form The fireball is made up of both the chemical that flash boils when the tank fails and the chemical that sprays out as an aerosol during the explosion ALOHA estimates that the amount of chemical in the fireball is three times the amount of chemical that flash boils Any liquid that does not participate in the fireball will form a pool fire When you choose to model a BLEVE situation in ALOHA the program estimates the thermal radiation from both fires it is not necessary to run an additional Pool Fire scenario The primary hazard associated with a fireball is thermal radiation However if there are other chemicals near the fireball it can trigger additional fires and explosions Explosion and hazardous fragments In a BLEVE a high pressure explosion typically causes the container to fragment As the container breaks apart it may strike objects in the
79. add the location to the library C Standard Time Daylight Savings Time Modifying a location You can modify the description of a city or other location in the city library You can modify the location name its approximate latitude and longitude its average elevation above sea level the state territory or country where it exists the local time setting and the GMT offset if it s a non U S location To change information that you ve already entered for a location choose Location from the SiteData menu to access the list of locations Click on its name in the location list then click Modify You will see the information about that location that is currently in the location library Delete the information that you wish to change then type in the new value Click OK Deleting a location To remove a location from the list choose Location from the SiteData menu to access the list of locations Click on its name in the location list then click Delete Click Cancel to avoid deleting the location click OK to delete the location from the list If you accidentally click OK to delete the wrong city once you ve returned to the Location dialog box click Cancel If instead you click Select to close this dialog box the city will be deleted Building Type For toxic gas dispersion scenarios ALOHA can estimate the pollutant gas concentration within buildings downwind Infiltration Building Parameters of a chemical release Note This set
80. ain 113 Chapter 4 Reference Wind speed direction and measurement height ALOHA needs to know the wind speed and direction as well as the height at which the wind speed and direction are measured The wind direction determines which way a pollutant cloud will drift The wind speed affects not only how fast the cloud will travel downwind but also how much it moves about in the crosswind and vertical directions When the wind is slower the cloud meanders more Atmospheric Options Wind Speed is 5 C knots mph meters sec Help Enter degrees true or text e g ESE Measurement Height above groundis Help A s a e A OR entervalue 10 ls meters Wind is from S Use Table 4 2 when you need to estimate the wind speed from environmental clues For example when the wind speed is 12 knots you would expect to see small branches of trees and bushes moving slightly and dust and loose paper blowing along the ground Table 4 2 Estimating wind speed from environmental clues One knot equals 1 15 miles per hour Meters per International Second Knots Description Specifications lt 1 lt 1 Calm Calm smoke rises vertically lt 1 2 1 3 Light air Direction of wind shown by smoke drift but not by wind vanes 2 3 4 6 Light breeze Wind felt on face leaves rustle ordinary vane moved by wind 4 5 7 10 Gentle breeze Leaves and small twigs in constant motion wind extends
81. ammable region of a vapor cloud These limits are percentages that represent the concentration of the fuel that is the chemical vapor in the air If the chemical vapor comes into contact with an ignition source it will burn only if its fuel air concentration is between the LEL and the UEL To some extent these properties are interrelated chemicals that are highly volatile and have a low flash point will usually also have a low LEL Once the chemical catches on fire three things need to be present to keep the fire going fuel the chemical oxygen and heat This is often referred to as the fuel triangle If any one of those components is eliminated then the fire will stop burning Like other reactions a fire can also generate byproducts smoke soot ash and new chemicals formed in the reaction Some of these reaction byproducts can be hazardous themselves While ALOHA cannot model all the complex processes that happen in a fire like the generation and distribution of byproducts it can predict the area where the heat radiated by the fire called thermal radiation could be harmful Thermal radiation is the primary hazard associated with fires However it is also important to consider the hazards associated with any secondary fires and explosions that may occur 19 Chapter 1 Welcome to ALOHA Thermal Radiation Levels of Concern A Thermal Radiation Level of Concern LOC is a threshold level of thermal radiation usually th
82. and outdoor air at the specified location during the first hour after the beginning of a chemical release The concentrations shown on the graph are averaged over a few minutes they are not instantaneous values Gas concentrations can fluctuate greatly over time periods of several seconds The maximum peak concentration can significantly exceed the maximum averaged concentration shown on the graph There may be up to five lines visible on the graph The thin red line represents the outdoor ground level concentration The dashed blue line represents concentration within a building of the type you selected To compute indoor concentration ALOHA assumes that all doors and windows are closed If applicable to your chosen location there may also be up to three horizontal lines red orange and yellow representing the LOCs The red horizontal line represents the worst hazard level Concentration at Point BEGL 3 60 min BEGL 2 60 min BEGL 1 60 min Outdoor Concentration Indoor Concentration t Point Downwind 1500 yards Off Centerline 0 yards In the Concentration at Point graph above ALOHA predicts that a cloud of chlorine gas would arrive at the location in about 7 minutes that s when the outdoor concentration line begins to rise steeply on the graph Notice that the indoor concentration is predicted to remain much lower than the outdoor concentration as long as the building s door and windows are closed ALOHA pr
83. ap in order to obtain a concentration estimate for the location where the workmen were injured Choosing a location and a chemical 1 Start ALOHA or if ALOHA is already running select New from the File menu to begin a new scenario you will be asked whether you wish to save a file of your previous work 2 Read the list of ALOHA s limitations click Help to see more details then click OK 3 Select Location from the SiteData menu A Location Information dialog box appears with a list of the names of cities included in ALOHA s location library 4 Manassas Virginia is not a location in ALOHA s library so you ll need to add it Click Add A Location Input dialog box appears 5 Manassas Virginia is a city in the United States located at 38 50 N and nics filllecalisa wane 77 30 W and with an elevation of 200 Location is MANASSAS feet Type MANASSAS in the location name box Select the In U S option Type 200 in the elevation box and select ft Type 38 in the latitude degree box and 50 in the latitude Location Input Is location in a U S state or territory Select state or territory In U S C Notin U S Enter approximate elevation Elevation is 200 Ct Cm minute box Select N Type 77 in the Enter approximate location VIRGIN ISLANDS deg min WAKE ISLAND a WASHINGTON O C Latitude 38 50 5 s WEST VIRGINIA longitude degree box and 30 in the longitude minute box Select W Sc
84. aporates Because several physical processes involved in a chemical release are affected by temperature use as accurate a value as possible Atmospheric Options 2 Air Temperature is 72 Degrees F CC Help Stability Classis Help C 4 BC f f g Override Inversion Height Options are Help feet No Inversion C Inversion Present Height is C meters 118 Chapter 4 Reference Stability class The atmosphere may be more or less turbulent at any given time depending on the amount of incoming solar radiation as well as other factors Meteorologists have defined six atmospheric stability classes each representing a different degree of turbulence in the atmosphere When moderate to strong incoming solar radiation heats air near the ground causing it to rise and generating large eddies the atmosphere is considered unstable relatively turbulent Unstable conditions are associated with atmospheric stability classes A and B When solar radiation is relatively weak or absent air near the surface has a reduced tendency to rise and less turbulence develops In this case the atmosphere is considered stable less turbulent the wind is weak and the stability class would be E or F Stability classes D and C represent conditions of more neutral stability moderate turbulence Neutral conditions are associated with relatively strong wind speeds and moderate solar radiation UNSTABLE STABLE ed pi BEUTRAL gt a ae jd k a
85. area of relatively high ground roughness such as residential housing developments industrial areas or forests The gas produced by the evaporation of a liquid or sublimation of a solid For example the gas produced when liquid water evaporates is water vapor 186 Glossary Vapor cloud explosion Vapor pressure Volatility Wind direction Wind Rose When a flammable chemical is released into the atmosphere it forms a vapor cloud that will disperse as it travels downwind If the cloud encounters an ignition source the parts of the cloud where the concentration is within the flammable range between the Lower and Upper Explosive Limits will burn The speed at which the flame front moves through the cloud determines whether it is a deflagration or a detonation In some situations the cloud will burn so fast that it creates an explosive force blast wave Two primary hazards are associated with a vapor cloud explosion overpressure and hazardous fragments Vapor pressure is a property of a liquid At equilibrium molecules move from the liquid to the gas phase at the same rate as they return to the liquid from the gas phase The vapor pressure is a measure of the concentration of gas phase molecules in the air directly in contact with the liquid at equilibrium In most actual cases equilibrium is not reached so the vapor pressure represents the limiting value for chemical concentration in the air The tendency of a li
86. as boiling point are often expressed at standard temperature 0 C and standard pressure 1 atmosphere A street bordered along both sides by high rise buildings that block air movement so that the wind and any dispersing pollutant cloud are channeled down the street A frozen substance sublimates when it passes directly into the gas phase without first becoming liquid Temporary Emergency Exposure Limits TEELs are temporary Toxic Levels of Concern LOCs similar to ERPGs and defined by the U S Department of Energy for use when ERPGs aren t available Unlike AEGLs and ERPGs TEELs are not peer reviewed and are intended as temporary guidance AEGLs ERPGs and TEELs do not incorporate safety factors Rather they are designed to represent the predicted response of members of the general public to different concentrations of a chemical during an incident The way in which land features such as hills and valleys modify the speed and direction of air flow Heat released during a fire and explosion that may pose a hazard to people and structures The effects people experience will depend on both the level of thermal radiation and the length of time they are exposed to it 184 Glossary Threat at Point Threat distance Threat zone Time dependent dispersion Time dependent source ALOHA can model one or more of the following hazards toxicity flammability thermal radiation or overpressure Once you have dis
87. as archive files and you can copy and paste graphs plots and text information from ALOHA into documents or reports in word processing or graphics programs 12 Chapter 1 Welcome to ALOHA ALOHA s menu bar Perform basic ALOHA operations by moving left to right through the seven menus in its menu bar File and Edit Choose items from these two menus to perform basic operations such as opening closing and saving files printing the contents of ALOHA s windows and copying text and graphics displayed in ALOHA SiteData Choose items from the SiteData menu to enter information about the release a the date and time b location and c the type of buildings downwind of a toxic gas release SetUp Choose items from the SetUp menu to a select a chemical from ALOHA s chemical library or to add a chemical to the library b indicate weather conditions manually or by connecting your computer to a portable meteorological station c set the source describe how the chemical is escaping from containment and d choose the type of dispersion calculations for ALOHA to make ALOHA can predict the movement of either neutrally buoyant clouds that are about as dense as air and heavy gas clouds that are denser than air Display Choose items from the Display menu to indicate the ALOHA results that you would like to see and to choose how you would like the information to be displayed Choose to tile or stack ALOHA s windows and choos
88. as passed For example if an evaporating puddle has substantially changed in area or the wind speed or direction has changed enter new atmospheric and source information into ALOHA and obtain an updated threat zone plot Release duration for vapor cloud explosions For vapor cloud explosions the release can be modeled for less than 1 minute However if your chosen release duration that is the time until the cloud ignites is less than one minute you will not get the maximum possible explosion Additionally if you are modelling an instantaneous release from a Direct source not all of the chemical will be released for times less than one minute because ALOHA models the release as a constant release with a one minute duration 129 Chapter 4 Reference ALOHA reports release rate When you use ALOHA s Puddle Tank or Gas Pipeline source options ALOHA reports the release rate in the Text Summary as the Maximum Average Sustained Release Rate or as the Maximum Burn Rate ALOHA computes release rate from a puddle tank or gas pipeline as a series of hundreds of brief timesteps Each timestep represents a rate of release that is maintained for a particular amount of time timesteps are short if release rate is changing rapidly and longer if release rate is nearly constant For releases into the atmosphere ALOHA averages this series of many release rates into between one and five release rates that are each for a time period of a
89. ast 1 minute For burn rates ALOHA averages over timesteps lasting 20 seconds The series of averaged steps is shown on the Source Strength graph since this is the information used to calculate the threat zones Tile and Stack Windows The Tile and Stack Windows options allow you to organize the information windows on your computer screen e Choose Tile Windows when you wish to see all of ALOHA s open windows at once rather than overlapping each other in a stack Windows will be reduced in size and arranged in rows and columns as necessary to fit on your screen e Select Stack Windows when you wish to arrange ALOHA s windows on your screen so that each overlaps the next with only the front window fully visible The title bars of the remaining windows will remain visible You may resize or move any ALOHA window after you have chosen either option Display Options Choose Display Options from the Display menu to have ALOHA output displayed in either Display Options Select Output Units English units e English units such as pounds yards and miles or oR canen e Metric units such as grams kilograms X meters and kilometers C Metric units Click either English units or Metric units ALOHA will display the results of its computations in the type of units English or metric that you choose It will display input values in the units that you selected when you entered the values For example if you entered wind
90. at it transmits data in a format that ALOHA can accept this format is described below Transmitting SAM data to ALOHA For use with ALOHA aSAM must meet several design criteria The SAM should sample wind speed and direction at a rate of at least one sample every 2 seconds It must transmit wind speed and direction and air temperature readings every 30 seconds Because air temperature does not change quickly over time it may be sampled less frequently than wind speed and direction Data transmitted from your SAM to ALOHA must be in the following free field comma delimited format ALOHA displays unprocessed SAM data in the same format lt cr gt lt lf gt ID VS WD SD TA SP DLTI B CHK Table 4 6 Translation key for SAM data codes Code Required Information lt cr gt Carriage return ASCII character code 13 lt lf gt Line feed ASCH character code 10 ID Station identification number VS Vector mean wind speed averaged over 5 minutes in meters per second WD Mean wind direction averaged over 5 minutes in degrees true SD Standard deviation of the wind direction sigma theta in degrees TA Mean air temperature averaged over 5 minutes in degrees Celsius SP Instantaneous wind speed in meters per second DI Instantaneous wind direction in degrees true TI Instantaneous air temperature in degrees Celsius B Instantaneous SAM battery voltage in volts CHK Checksum computed by summing the ASCII values
91. ation Level of congestion in the flammable part of the vapor cloud Heip C congested difficult to walk through e g pipe rack dense forest uncongested easy to walk through e g residential neighborhood Cancel Next choose the ignition type The type of ignition source has a big influence on the severity of the explosion Accidental explosions are most often triggered by common ignition sources such as sparks flames heat and static electricity Accidental explosions are generally deflagration explosions Explosions that are triggered by detonation usually by a high power explosive device are detonation explosions which are far more damaging than deflagration explosions Under rare circumstances an accidental explosion can be triggered by a common ignition source and still become a detonation explosion If you know the ignition type choose the appropriate option If you are using ALOHA for planning purposes consider modeling both types of ignition Choose the ignited by spark or flame option if you want to model a typical accidental explosion Choose the ignited by detonation option if you want to model an intentional explosion or a worst case accidental explosion Finally choose the congestion level within the majority of the vapor cloud Congestion refers to the density of obstacles that generate turbulence Obstacles of this nature are generally small like a shrub and do not impede the flame front Larger objects l
92. avy gas release it bases this choice mainly on molecular weight size of the release and temperature of the gas cloud But sometimes you may want to specify the model to use rather than letting ALOHA choose In particular when a chemical with a molecular weight less than that of air has been stored at a low temperature or under high pressure it can behave like a heavy gas ammonia is an example of such a chemical If you have chosen one of these chemicals depending on how you model its release ALOHA may not have enough information about the release to determine whether a heavy gas could be formed In such a case ALOHA will make Gaussian calculations but will alert you that you should try running the heavy gas model as well In such cases you should re run ALOHA using the heavy gas calculations and compare the threat zone estimates Introduction to fires and explosions Beginning with ALOHA version 5 4 you can model fire and explosion scenarios as well as toxic gas dispersion scenarios This section provides basic information about fires and explosions and then explains how to model fires and explosions in ALOHA ALOHA allows you to model chemical releases from four types of sources Direct Puddle Tank and Gas Pipeline Refer to Table 1 1 to see what types of scenarios you can run in ALOHA from each source For a more detailed discussion on sources see Source on page 128 Table 1 1 ALOHA sources and scenarios
93. because it is heavier than the surrounding air As the gas cloud moves downwind gravity makes it spread this can cause some of the vapor to travel upwind of its release point Figure 1 2 Farther downwind as the cloud becomes more diluted and its density approaches that of air it begins behaving like a neutrally buoyant gas This takes place when the concentration of heavy gas in the surrounding air drops below about 1 percent 10 000 parts per million For many small releases this will occur in the first few yards meters For large releases this may happen much further downwind Figure 1 2 Cloud spread as a result of gravity The heavy gas dispersion calculations that are used in ALOHA are based on those used in the DEGADIS model Spicer and Havens 1989 one of several well known heavy gas models This model was selected because of its general acceptance and the extensive testing that was carried out by its authors Classification of heavy gases A gas that has a molecular weight greater than that of air the average molecular weight of air is about 29 kilograms per kilomole will form a heavy gas cloud if enough gas is released Gases that are lighter than air at room temperature but that are stored in a cryogenic low temperature state can also form heavy gas clouds If the density of a gas cloud is substantially greater than the density of the air the density of air is about 1 1 kilograms per cubic meter ALOHA considers the gas
94. between one and five release rates that are each for a time period of at least 1 minute For burn rates ALOHA averages over timesteps lasting 20 seconds The Maximum Average Sustained Release Rate or the Maximum Burn Rate if applicable is the highest of these averaged release rates It is represented by the tallest timestep on the Source Strength graph 179 Glossary Mixing Mole Molecular weight Neutrally buoyant gas Open Country Open Water Overpressure Partial pressure The process by which air is mixed into a pollutant gas cloud This includes both mechanical induced by the wind passing over rough ground and thermal induced by surface heating mixing Amount of a substance containing 6 02 x 1073 molecules The molecular weight of a chemical is the mass of 1 mole of that chemical The sum of the atomic weights of all the atoms in the molecule the weight of one molecule of the chemical A gas that is about as dense as air and neither positively nor negatively buoyant neither rises nor sinks in air An area of low ground roughness such as a parking lot or open field A body of water that is large relative to the size of the pollutant cloud that is travelling over it such as oceans or large lakes Except when the wind speed is very high Open Water is the lowest ground roughness category in ALOHA Overpressure also called a blast wave refers to the sudden onset of a pressure wave after an exp
95. bility Classis Help C 4 B E G E Override Inversion Height Options are Help that you ve entered to automatically a a a ae EA Paes select atmospheric Stability Class B Select Humidity Help Stability is a measure of the amount of bat i turbulence in the atmosphere the more 5 C OR C enter value 50 9 turbulent the air the more quickly a medium dry 0 100 pollutant cloud is diluted B is a relatively less stable that is more turbulent stability class Cancel There is no low level inversion Check to be sure that No Inversion is selected The relative humidity is about 50 percent Select the icon for medium humidity Notice that ALOHA has filled in a value of 50 percent Click OK 37 Chapter 2 Learning the Basics Describing the release Now you re ready to enter information about the release itself that is to set the source for this scenario 1 The chlorine at the treatment plant is stored in tanks In the SetUp menu point to Source then select Tank A Tank Size and Orientation dialog box appears The chlorine is stored in horizontal standard 1 ton containers that are 2 5 feet in diameter and 6 8 feet long Select Horizontal cylinder Type 2 5 in the diameter box then select feet Type 6 8 in the length box Notice that ALOHA automatically calculates the tank volume Click OK A Chemical State and Temperature dialog box appears Chlorine is a gas at ambient tempe
96. bility of hazardous fragments and take necessary precautions to shield responders and others from the potentially fatal fragments Some hazardous fragments may be projected into areas well beyond those affected by the thermal or overpressure explosion hazards Analysis of data from multiple accident investigations revealed several broad trends that responders should keep in mind regarding hazardous fragments Leslie and Birk 1991 e 80 of fires that lead to container rupture result in missiles e g hazardous fragments e 80 of fragments from liquid petroleum gas LPG accidents travel less than 200 meters 660 feet e Spherical containers produce more missiles than cylindrical containers spheres average 8 3 missiles and cylinders average less than 4 missiles e End tubes from cylindrical containers travel further than other types of fragments e Smaller vessels project fragments further than larger ones and e Missiles tend to export fire with them Why doesn t ALOHA model hazardous fragments It is difficult to predict the distribution of hazardous fragments with any accuracy because there are too many unknown or unknowable variables The two main issues of concern are 1 the number of hazardous fragments and 2 where the fragments will land Types of fire and explosion scenarios ALOHA models the five types of fire and explosion scenarios that are most frequently associated with chemical releases Jet Fires Pool Fire
97. bject Name Place Map Gallerher Rd Gainesville CDP Y Galley Ct Lake Ridge CDP Y Gallop Ln Prince William County VA make all other objects on these layers invisible Save Collection Show All on Map Load Collection Addresses Show on Map amp Zoom Help Show on Map Close 94 Chapter 3 Examples 7 There are five intersections along Gallerher Road Click to highlight Lee Hwy in the list then click Show on Map amp Zoom Intersections Intersections for object Gallerher Rd on layer Roads of map Prince William County YA F Intersect with all layers Number of intersections found 5 plus 4 aliases Object Name Layer Place Map Gainesville Village Sq Roads Gainesville CDP John Marshall Hwy Roads Major Gainesville CDP Lee Hwy Roads Major Gainesville CDP Linton Hall Rd Roads Gainesville CDP State Foute 85 fiahn Marsha Hyg Roads Major Gainesville CDP State Boute 99 Linton Hat Ra Roads Gainesville CDP iinta States Away 29 flee Hay Roads Major Gainesville CDP Washington St fata AMarshat Avy Roads Major Gainesville CDP Show on Map Show on Map amp Zoom N Cancel Help A map similar to the one below appears Lee Hwy crosses the map as a straight line from the lower left to the upper right of the map The Norfolk Southern Railway crosses the map horizontally and intersects with Lee Hwy near the right side of the map Your map may look
98. c View Pure Chemicals Solutions AQUEOUS AMMONIA HYDROCHLORIC ACID HYDROFLUORIC ACID NITRIC ACID OLEUM Cancel Solution Strength 30 by Weight The percentage of ammonia in solution Allowable range is 0 to 30 percent 108 Chapter 4 Reference Reactive chemicals ALOHA assumes that the molecules in the released chemical do not react with each other or with the gases that make up the atmosphere such as oxygen and water vapor That is ALOHA assumes that the molecules that disperse in the atmosphere are the same molecules that originally escaped from a container However some chemicals react with dry or humid air water other chemicals or even themselves Because of these chemical reactions some or all of the molecules that disperse downwind sometimes may be very different from the molecules that originally escaped from containment They may be heavier or lighter than the original molecules may have different properties and behave differently in the atmosphere and may be more or less toxic than the original chemical In some cases these differences may be substantial enough to make ALOHA s predictions inaccurate ALOHA will allow you to model any reactive chemical as a non reactive chemical but it will warn you that it may not be able to produce accurate results When you select an air A Warning or water reactive chemical ALOHA will alert you that the PHOSPHORUS TRICHLORIDE can react with
99. cal is not burning and forms an evaporating puddle C Leaking tank chemical is burning and forms a pool fire C BLEVE tank explodes and chemical burns in a fireball Potential hazards from flammable chemical which is not burning as it leaks from tank Downwind toxic effects Vapor cloud flash fire Overpressure blast force from vapor cloud explosion Cancel 54 Chapter 3 Examples 6 The benzene is leaking from a 6 inch circular hole Check to be sure that Circular opening is selected Type 6 in the opening diameter box and select inches Choose the Hole option Click OK A Height of the Tank Opening dialog box appears Area and Type of Leak Select the shape that best represents the shape of the opening through which the pollutant is exiting Cc wns lt length Circular opening C Rectangular opening inches C feet Opening diameter 6 C centimeters C meters Is leak through a hole or short pipe valve Hole C Short pipe valve Cancel Help The hole is 10 inches above the bottom of the tank Type 10 in the bottom of the leak box and select in Notice that ALOHA fills in the other values Click OK A Puddle Parameters dialog box appears Height of the Tank Opening liq level E The bottom of the leak is so as ft C cm Cm above the bottom of the tank iz _ OF xl of the way to the top of the tank Cancel Help 55 Chapter 3 Examples
100. ch properties are necessary for ALOHA s various source and dispersion options To enter additional property values click on the name of each property in the scrolling list of property names or click Next Field until the property name is highlighted Type property values in the appropriate boxes then choose units You must add a reference temperature and pressure for all properties that change their values when temperature and or pressure changes For example if you were adding a fictional chemical such as methyl ethyl death into the chemical library you would need to know that it has a gas heat capacity of 1 500 joules per kilogram Kelvin at a temperature of 320 Kelvin and a pressure of 101 325 pascals Input Available Information Chemical Name Methyl Ethyl Death Molecular Weight 42 gimol Default LOC 3 Red A Heat Cap gcp Value 1500 Density gas ERPG 1 Ji kg K ERPG 2 ERPG 3 Heat Cap gcp Temperature 320 Kelvin Heat of Combustion Heat Cap gcp Pressure 101325 IDLH v Pa Next Field Cancel Once you have entered all information about a new chemical click OK to permanently add your new chemical to ALOHA s chemical library The Chemical Information dialog box appears with the newly updated list of chemicals in ALOHA s chemical library Click Select to select the chemical that you ve just added Click Cancel if you decide not to permanently add the chemical to t
101. components are interspersed uniformly at the molecular level ALOHA s chemical library includes a short list of solutions Most are solutions of an anhydrous acid and water e g hydrogen fluoride and water In all cases only one component of the solution is both toxic and volatile enough to pose an air hazard For example in hydrofluoric acid a solution of hydrogen fluoride and water it is the hydrogen fluoride that is the air hazard The vessel or pool releasing a hazardous chemical into the atmosphere The distance above the ground at which a chemical is being released Either the rate the chemical enters the atmosphere or the burn rate depending on the scenario A chemical may escape very quickly so that source strength is high as when a pressurized container is ruptured or more slowly over a longer period of time so that source strength is low as when a puddle evaporates See Atmospheric stability The atmosphere is stable when little air turbulence exists so that there is little tendency for air to be mixed into a dispersing pollutant cloud 183 Glossary Standard deviation STP Street canyon Sublimation TEELs Terrain steering Thermal radiation A measure of the degree to which individual values deviate from an average value Computed as the square root of the sum of the squared deviations divided by the number of measurements Standard Temperature and Pressure Physical properties such
102. d 128 916 pounds Note The chemical escaped from the tank and burned as a jet fire 82 Chapter 3 Examples Choosing LOCs and creating a threat zone plot for a jet fire 1 Choose Threat Zone from the Display menu A Thermal Radiation Level of Concern dialog box appears 2 You want to know the thermal radiation threat for the jet fire Keep ALOHA s default LOCs and click OK ALOHA will display a threat zone plot for this release You ll see ALOHA s threat zone plot for this scenario showing three thermal radiation threat zones ALOHA estimates that the red threat zone the worst hazard level will extend about 50 yards in all directions and a little farther in the downwind direction The orange and yellow threat zones represent areas of decreasing hazard It is important to realize that there may be additional hazards that are not modeled by ALOHA including secondary fires and explosions Thermal Radiation Threat Zone 150 200 100 e m yards gt 10 0 kW sq m potentially lethal within 60 sec gt 5 0 kKW sq m 2nd degree burns within 60 sec gt 2 0 kW sq m pain within 60 sec Check the Text Summary for this release Text Summary THREAT ZONE Threat Modeled Thermal radiation from jet fire Red 58 yards 10 0 kW sq m potentially lethal within 66 sec Orange 83 yards 5 6 kW sq m 2nd degree burns within 66 sec Yellow 129 yards 2 6 kW sq m pain within
103. d ability to escape AEGL 3 The airborne concentration of a substance above which it is predicted that the general population including susceptible individuals could experience life threatening health effects or death Each of the three levels of AEGL AEGL 1 AEGL 2 and AEGL 3 are established for each of five exposure periods 10 minutes 30 minutes 60 minutes 4 hours and 8 hours Note In ALOHA the 60 minute AEGL exposure limits are the default toxic LOCs when available Toxic Level of Concern Select Toxic Level of Concern Red Threat Zone Loc PEGE Orange Threat Zone Loc AEGL 2 60 min 2 ppm z Yellow Threat Zone Loc AEGL 1 60 min 0 5 ppm X Show confidence lines only for longest threat zone C for each threat zone Cancel 3 Inthe Show confidence lines section check to be sure that only for the longest threat zone option is selected Click OK A Toxic Threat Zone window appears 44 Chapter 2 Learning the Basics Examine ALOHA s threat zone plot for this scenario On the plot the red orange and yellow regions represent the areas where chlorine concentrations are predicted to exceed the corresponding LOC values in this case the AEGL values at some time after the release begins The red AEGL 3 threat zone the area with the greatest exposure level is predicted to extend more than half a mile downwind of the leaking cylinder The orange AEGL 2 threat zone is predicted
104. d by modelers to include advection moving and diffusion spreading A dispersing vapor cloud will generally move advect in a downwind direction and spread diffuse in a crosswind and vertical direction crosswind is the direction perpendicular to the wind A cloud of gas that is denser or heavier than air called a heavy gas can also spread upwind to a small extent ALOHA can model the dispersion of a cloud of pollutant gas in the atmosphere and display a diagram that shows an overhead view of the regions or threat zones in which it predicts that key hazard levels LOCs will be exceeded This diagram is called a threat zone plot To obtain a threat zone estimate you must first choose at least one LOC ALOHA will suggest default LOCs and you may keep those or choose up to three other LOCs For toxic gas dispersion scenarios an LOC is a threshold concentration of the gas at ground level usually the concentration above which a hazard is believed to exist The type of LOC will depend on the scenario For each LOC you choose ALOHA estimates a threat zone where the hazard is predicted to exceed that LOC at some time after a release begins These zones are displayed on a single threat zone plot If three LOCs are chosen ALOHA will display the threat zones in red orange and yellow When you use ALOHA s default LOCs the red zone represents the worst hazard There are two separate dispersion models in ALOHA Gaussian and heavy gas Gaussian m
105. d feet in elevation of the actual site Adding information about a U S city Choose Location from the SiteData menu to access the list of locations Click Add In the dialog box that appears type the location s name approximate latitude and longitude and elevation then click on the name of its state or territory in the scrolling list of U S states and territories on the right side of the window click anywhere within the list then type the first letter of the state or territory name to quickly move to that letter s location in the list ALOHA checks that the information you have entered is within the range of reasonable values for the state or territory that you select If you have entered a value that is not in this range ALOHA will tell you which value is out of range you must correct your value before continuing Click OK Location Input Enter full location name Locationis Jupiter Is location in a U S state or territory Select state or territo inUS Notin U S be ae CONNECTICUT sa Enter approximate elevation DELAWARE Elevation is 50 Ct Cm DIST OF COLUMBIA GEORGIA GUAM deg min HAWAII i ZATA IDAHO ie l4 Latitude 26 57 N CS ILLINOIS Longitude 80 08 t JES DOY Cancel Enter approximate location 102 Chapter 4 Reference Unless the location is in a state with multiple time zones ALOHA automatically recognizes the location s time zone and also adjusts time of day for da
106. d liquid is stored in the tank ALOHA will report that no chemical is released Regardless of the height of the leak however if the stored chemical is stored as a liquefied gas it will escape through the opening directly into the atmosphere without forming a puddle as a two phase flow of gas and aerosol fine liquid droplets To indicate the height of the leak above the tank bottom either e Type the height of the leak in distance units e Type the leak location as a percentage of the total distance from the bottom of the leak to the top of the tank for example 90 means that the leak is 90 of the way to the top of the tank or e Use the scroll bar to the right of the tank diagram to indicate the height of the leak on the tank wall Height of the Tank Opening The bottom of the leak is 1 25 Cin Cft C cm Cm liq level al above the bottom of the tank C E OR 50 of the way to the top of the tank Cancel Help If the chemical is an unpressurized liquid you will need to enter some more information about the puddle that forms Puddle formation If an unpressurized liquid leaks from a tank an evaporating puddle may be formed ALOHA will ask you for information about the area where the puddle will form You will need to enter ground type and ground temperature just as you would if you had selected the Puddle source option however in a Tank release case ALOHA computes initial puddle temperature for you Y
107. dale 100 SiteData MOI och os ee ee oina vine eal es i a lassie aloyn ln Lita S cause alata ates 101 LOCAUON 2 4 ETT 101 Selecting a LOCAL ON aussi tees elt at eater seth Ratan Goleta ol eee altace 101 Adding information about a U S City eee ceseceeeeeseeceaeeeeeeeeeeeeneeeaeens 102 Adding a location outside the U S cee eeescecsseeeceeececeeeceseeeeceeeeeseeeeeees 103 Modifying a locat ON biotite ok een enn hittin unde 104 Deleting a locatio segetes stes leas sere guser easter uaa 104 BUS Typeset e E E 104 Date TMe e a a A alate A tel R Mei ASIR iS 106 Table of Contents SetUp menu eee eee ONAN SNE eM E Oe Ee CRU ANC RT Ae eS eee a ANNE ee ane ee 107 Chemicals behets ha eR att IA Needed oe aa ee 107 Selecting a pure Chemical iicisacc dcassevcavesesssccessnccsvsscevedeatassaceesacereenseoessoceaya 108 Selecting a chemical solution sa 20 cetusheedecgeeae te eee is a eect 108 FRG ACTIVES 10M TNC AS est ast serie chads at A oe acne edit al par el a E ct 109 Chemical information in the Text Summary window eeeeeeeereeees 109 Chemicakdatanars Sneons a e Ne mtn e aa a Rn nee 110 Adding a chemical to the library sneesessenseeesseessseesseesseseseessesessseessese 112 Modifying a chemical entry in the library sssseseseeeeseeesseesseesseresseeessee 112 Deleting a chemical from the library 0 eee eeeeeseecseceeeeeeeeeeaeeeaeens 113 PAUIMOS PHOT Crank ies de swpssoay E a a stiles aakeweascaes ane a ET 113
108. e Threat Zone 100 200 yards 8 0 psi destruction of buildings 3 5 psi serious injury likely 1 0 psi shatters glass onfidence Lines Text Summary THREAT ZONE Threat Modeled Overpressure blast force from vapor cloud explosion Type of Ignition ignited by spark or flame Level of Congestion congested Model Run Heavy Gas Red LOC was never exceeded 8 6 psi destruction of buildings Orange 129 yards 3 5 psi serious injury likely Yellow 221 yards 1 6 psi shatters glass 80 Chapter 3 Examples Compare the flammable vapor cloud threat zone plots Below the flammable area threat zone plot is shown on the left and the congested vapor cloud explosion threat zone plot is on the right threat distances from the Text Summary screens for all of the flammable vapor cloud scenarios are summarized in a table E Flammable Threat Zone 200 300 400 00 yards gt 0 psi destruction of buildings 12 000 ppm 60 LEL Flame Pockets s 3 5 psi serious injury likely gt 2 000 ppm 108 LEL 1 0 psi shatters glass Contidence Lines Comtidence Lines The flammable area red threat zone is estimated to extend 171 yards downwind This is the area where ALOHA predicts a flash fire or a vapor cloud explosion could occur at some point after the release begins depending on the release conditions congestion level and availability of ignition sources When you
109. e U S cloud cover is usually measured in tenths when the sky is completely covered by clouds cloud cover is 10 tenths when half the sky is covered by clouds it is 5 tenths when the sky is completely clear it is 0 tenths These values are represented by the complete cover partly cloudy and clear icons respectively Atmospheric Options Wind Speed is 5 C knots mph meters sec Help Wind is from Ss Enter degrees true or text e g ESE Measurement Height above ground is Help C a e A OR entervalue 10 f fect 22th meters Ground Roughness is Help Open Country C s C Urban or Forest OR Input Roughness Zo C Open Water Select Cloud Cover Help at g OR entervalue 3 Cc s C 0 10 complete partly clear cover cloudy Cc e Cancel To select cloud cover either e Click the button corresponding to either 0 3 5 7 or 10 tenths or e Type a whole number between 0 and 10 in the box for cloud cover value in tenths for example type 6 if cloud cover is 6 tenths Air temperature ALOHA requires a value for the air temperature in the vicinity of a chemical release You can enter a value in either degrees Fahrenheit F or degrees Celsius C Air temperature influences ALOHA s estimate of the evaporation rate from a puddle surface the higher the air temperature the more the puddle is warmed by the air above it the higher the liquid s vapor pressure is and the faster the substance ev
110. e has been selected Click OK ALOHA will display a threat zone plot for this chlorine release Toxic Level of Concern Select Toxic Level of Concern Red Threat Zone Loc AEGL 3 60 min 20 ppm bd Orange Threat Zone Loc AEGL 2 60 min 2 ppm 5 Yellow Threat Zone Loc AEGL 1 60 min 0 5 ppm z Show confidence lines only for longest threat zone C for each threat zone Cancel 90 Chapter 3 Examples P Toxic Threat Zone 20 ppm AEGL 3 60 min 2 ppm AEGL 2 60 min gt 0 5 ppm AEGL 1 60 min Confidence Lines Check the Text Summary to see the lengths of the three threat zones For example ALOHA expects the red threat zone which exceeds the AEGL 3 20 ppm value to extend at least 1 484 yards downwind Text Summary SITE DATA Location MANASSAS VIRGINIA Building Air Exchanges Per Hour 6 58 unsheltered single storied Time June 4 2666 1566 hours EDT user specified CHEMICAL DATA Chemical Name CHLORINE Molecular Weight 76 91 g mol AEGL 1 66 min 6 5 ppm AEGL 2 66 min 2 ppm AEGL 3 66 min 26 ppm IDLH 16 ppm Carcinogenic risk see CAHEO Ambient Boiling Point 29 5 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 666 ppm or 166 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 6 miles hour from E at 3 meters Ground Roughness open country Cloud Cover 3 tenths Air Temperature 72 F Stability Cla
111. e level above which a hazard may exist When you run a fire scenario ALOHA will suggest three default LOC values ALOHA uses three threshold values measured in kilowatts per square meter and denoted as kW m to create the default threat zones e Red 10 kW m potentially lethal within 60 sec e Orange 5 kW m second degree burns within 60 sec and e Yellow 2 kW m pain within 60 sec The thermal radiation effects that people experience depend upon the length of time they are exposed to a specific thermal radiation level Longer exposure durations even at a lower thermal radiation level can produce serious physiological effects The threat zones displayed by ALOHA represent thermal radiation levels the accompanying text indicates the effects on people who are exposed to those thermal radiation levels but are able to seek shelter within one minute ALOHA s default thermal radiation values are based on a review of several widely accepted sources for this topic e g American Institute of Chemical Engineers 1994 Federal Emergency Management Agency et al 1988 and Lees 2001 If you set your own LOC values consider Table 1 2 Federal Emergency Management Agency et al 1988 which lists some physiological effects at specific thermal radiation levels and durations on bare skin Table 1 2 Thermal radiation burn injury criteria Radiation Intensity kW m Time for Severe Pain s Time for 2nd Degree Burn
112. e pipe What should I do I am using a SAM with ALOHA I have set the SAM options using the Atmospheric menu but the Source menu is not available I can t set my source ALOHA tells me that the input value I just entered is not within allowable limits These properties are estimated by ALOHA from other information in its chemical library To use different property values add a new chemical use a name such as CHLORINE 2 then enter new property values If the pipe is too short relative to its diameter and its diameter is greater than about 8 inches 20 centimeters use the Tank option instead selecting the configuration of a horizontal tank If the pipe is less than 1 meter long and connected to a tank you also can use the Tank option in this case select Short pipe valve as the type of leak Either of these methods should produce a conservative threat estimate Either the SAM has not yet been collecting data for 5 minutes or ALOHA has not received valid data Before ALOHA can estimate atmospheric stability it must have received data from the SAM for at least 5 minutes Check the Text Summary window for a message alerting you that either the SAM has not been transmitting for 5 minutes or the transmitted data are not valid ALOHA will accept a numeric input value that is a value such as puddle area or tank hole diameter that you enter as a number only if it is within a specified range These restrictions help to
113. e puddle evaporation Exit menu item 100 explosion explanation of 21 hazardous fragments 23 overpressure 21 thermal radiation 21 F File menu 99 100 fire explanation of 19 fuel triangle 19 thermal radiation 20 toxic byproducts 19 fireball 25 190 Index fires and explosions ALOHA scenarios 23 27 flammable toxic chemicals 19 introduction to 18 23 sources and scenarios table 18 flame jet See jet fire flame pockets 26 flammability limits 19 flammable area explanation of 26 flame pockets 26 flammable 174 flash fire 26 flash point 19 flash boil BLEVE 25 definition of 175 heavy gas 17 flying debris See hazardous fragments footprint 12 freezing point 175 fuel reactivity 176 fuel triangle 19 fugitive emissions 15 fumes 176 G Gas Pipeline source 146 147 hole size 147 infinite reservoir 146 pipe diameter 146 pipe length troubleshooting 164 pipe length 146 pipe pressure 147 pipe roughness 146 pipe temperature 147 Text Summary 147 Gaussian definition of 176 dispersion 16 GIS 153 GMT Greenwich Mean Time 103 176 Greenwich Mean Time GMT 103 176 ground roughness about 116 choosing a type 116 roughness length 117 ground temperature 136 145 ground type 135 145 H hazardous fragments BLEVE 25 definition of 177 explanation of 23 from overpressure 21 heavy gas definition of 177 dispersion 17 inversions 121 propert
114. e puddle would not spread out as far because the liquid flowing away from the tank would fill up the depressions in the ground The puddle would then be smaller in area and deeper It would evaporate at a slower rate and it would take longer to completely evaporate Because ALOHA assumes that the puddle is on a perfectly flat surface and would spread out until it was very thin ALOHA may overestimate the real puddle size and evaporation rate At a real accident scene check for terrain features that would constrain the puddle from spreading use this information to estimate the maximum puddle area 57 Chapter 3 Examples Checking the Calculation and Display Options Settings You don t know if the toxic gas is a heavy gas or not so you ll want ALOHA to use information about the properties of the chemical and the amount of chemical released to choose whether to make Gaussian or heavy gas dispersion computations Check to be sure that ALOHA is set to this default 1 Select Calculation Options from the SetUp menu A Calculation Options dialog box appears 2 Check to be sure that Let ALOHA decide select this if unsure is selected Click OK Calculation Options Select the Spreading Algorithm for Downwind Dispersion Let ALOHA decide select this if unsure C Use Gaussian dispersion only C Use Heavy Gas dispersion only Cancel 3 Select Display Options from the Display menu A Display Options dialog box appears Selec
115. e that ALOHA has filled in a value of 10 meters 36 Chapter 2 Learning the Basics The exact ground roughness a measure of the unevenness or roughness of the terrain over which the gas cloud passes is not known but the accident occurs in a Atmospheric Options Wind Speed is 5 C knots mph meters sec Help Wind is from Ly Enter degrees true or text e g ESE Measurement Height above groundis Help rural farming area open fields with few C feet ae c 4 OR entervalue 10 a trees and buildings In ALOHA ground 4d aR Scag meters roughness can be entered explicitly if Ground Euunbnee lee Help the exact roughness number is known a gba OR Input Roughness Zo or implicitly by choosing a C Open Water representative type of terrain Select the Select Cloud Cover Help Open Country ground roughness ira zg option EO G OR enter value B 3 c c c c 0 10 About 3 tenths of the sky is covered by eee sae hee clouds Under Select Cloud Cover cover cloudy choose the fourth option from the left FER the option between the partly cloudy and clear options Notice that ALOHA has filled in a value of 3 Click OK The second Atmospheric Options dialog box appears The air temperature is 72 F Type 72 in the air temperature box then select F ALOHA uses the wind speed cloud cover and date and time information Atmospheric Options 2 Air Temperature is 72 Degrees F CC Help Sta
116. e upward transport of a gas plume such as smokestack gases which rise because they have been heated ALOHA does not account for plume rise A pool fire occurs when a flammable liquid forms a puddle on the ground and catches on fire ALOHA only models pool fires on land it does not model pool fires on water Thermal radiation is the primary hazard associated with a pool fire Other potential pool fire hazards include smoke toxic byproducts from the fire and secondary fires and explosions in the surrounding area The ratio of the amount of water vapor that the air contains to the maximum amount of water vapor that it could hold at the ambient temperature and pressure Relative humidity is expressed as a percentage When relative humidity is 50 the air contains one half as much water vapor as it could potentially hold The period of time over which a release occurs ALOHA limits release duration to 1 hour 181 Glossary Roughness length Running average SAM Save file Serial port Sigma theta Smoke Solubility Also Z A numerical measure of ground roughness An average taken in consecutive overlapping segments e g the average of the first five values then the average of the second through sixth values then the average of the third through seventh values etc Station for Atmospheric Measurements A portable meteorological measurement station that can transmit weather data to ALOHA through a c
117. e whether to see ALOHA s results displayed in English or metric units Choose one or more LOCs and display the threat zone plot If applicable given your scenario you may also choose to display a threat at point report or a source strength graph Sharing Choose items from this menu to a display an ALOHA threat zone on a background map using MARPLOT the CAMEO mapping module or b see detailed information about the chemical you ve selected displayed in CAMEO s Response Information Data Sheets RIDS module Help Choose items from the Help menu to see the help topics list and to get information about ALOHA 13 Chapter 1 Welcome to ALOHA Getting help On screen help is available when ALOHA is running The list of help topics can be accessed through the Help menu Also most screens have Help buttons that take you to a screen specific help topic File Edit Bookmark Options Help Contents Index Print ALOHA Help Topics Infiltration Building Parameters Adding or modifying chemical data Select building type or enter exchange parameter Adding or modifying location data i AEGL C Enclosed office building tele Air temperature Single storied building ALOHA limitations C Double storied building Ambient saturation concentration No of air changes is z per hour Atmospheric BLEVE oint ing Type Burn rate maximum Calculation Options In Windows To see the list of help topics
118. e wind speed 2 SS reaches a maximum because it is no longer affected by s friction as shown at the right in a wind profile z Indicate the wind measurement height in the Measurement r height above ground section Choose one of the following three options to indicate the height e SAMs typically are mounted on a 3 meter 9 8 foot WIND SPEED stand so the wind reference height for readings from a SAM is likely to be 3 meters Select the icon on the left the one with the close up view of a person to indicate a height of 3 meters this is ALOHA s default measurement height e The National Weather Service usually reports wind speed measured at a height of 10 meters about 33 feet Select the icon on the right the one of the tower to indicate a height of 10 meters e If you know that your wind speed value is being measured at a different height type that height in the measurement height box then choose units 115 Chapter 4 Reference Ground roughness The degree of atmospheric turbulence influences how quickly a pollutant cloud moving downwind will mix with the air around it and be diluted below your LOC Friction between the ground and air passing over it is one cause of atmospheric turbulence Because the air nearest the ground is slowed the most eddies develop just as they would in the water next to a riverbank The rougher the ground surface the greater the ground roughness and the greater the turbulence that
119. eactive chemicals 31 109 selecting a chemical 108 selecting a solution 108 CityLib 101 cloud cover 118 concentration average 30 definition of 172 patchiness near source 30 Threat at Point 155 Concentration at Point graph 155 concentration patchiness 26 30 189 Index confidence lines threat zone plot 152 very low wind speeds 28 confinement 27 congested 27 congestion 27 conservative 172 continuous release 131 Coordinated Universal Time 176 coordinates fixed 154 coordinates relative 154 Copy menu item 100 crosswind 16 cryogenic definition of 172 heavy gas 17 Puddle source 135 Tank source 144 D Date amp Time menu item 106 daylight savings time at non U S locations 104 at U S locations 103 definition of 173 multiple time zones 103 deflagration explosion 27 DEGADIS model 17 dense gas dispersion 17 density 173 detonation explosion 27 diffusion 16 Direct source 130 132 continuous release 131 instantaneous release 131 source height 132 threat zones 131 dispersion choice of model 18 dispersion modeling 15 18 Gaussian 16 heavy gas 17 particulates 31 radioactive particles 31 stability class 119 street canyon 29 terrain steering 29 Display menu 149 158 Display Options menu item 158 display units 158 double storied building 105 E eddies 29 174 Edit menu 100 elevation 102 English units 158 ERPGs 174 evaporating puddle Se
120. ears Liquid Mass or Volume Enter the mass in the tank OR volume of the liquid C pounds The mass inthe tankis 701 tons 2 000 Ibs C kilograms n Enter liquid level OR volume gallons The liquid volume is 33800 cubic feet C liters C cubic meters 100 full by volume ba Cancel Help 5 You want to begin by modeling the potential BLEVE scenario Choose the BLEVE tank explodes and chemical burns in a fireball option Click OK Type of Tank Failure Scenario Tank containing a pressurized flammable liquid Type of Tank Failure C Leaking tank chemical is not burning as it escapes into the atmosphere C Leaking tank chemical is burning as a jet fire BLEVE tank explodes and chemical burns in a fireball Potential hazards from BLEYE Thermal radiation from fireball and pool fire Hazardous fragments and blast force from explosion cannot be modeled by ALOHA Downwind toxic effects of fire byproducts cannot be modeled by ALOHA Cancel 71 Chapter 3 Examples The source strength information that you have entered and the results of ALOHA s source strength calculations appear in the Text Summary ALOHA estimates that the BLEVE fireball has a diameter of about 253 yards and burns for about 14 seconds Text Summary SITE DATA Location COLUMBIA SOUTH CAROLINA Building Air Exchanges Per Hour 6 52 unsheltered single storied Time June 25 2066 1236 hours EDT us
121. eat Point The ALOHA window will come to the front and it will display a Concentration at Point graph for this location threat at point Review the graph and the Text Summary ALOHA estimated that the workmen were exposed to an outdoor concentration above the AEGL 2 level for roughly three minutes Note Your graph may differ slightly from the one below if you click on a slightly different point on the map when setting your threat point P Concentration at Point AEGL 3 60 min AEGL 2 60 min AEGL 1 60 min minutes Outdoor Concentration Indoor Concentration t Point West 334 yards South 121 yards Don t be concerned if the numbers that you see on your screen differ slightly from those shown in the Text Summary ALOHA s estimates are affected by exactly where on the map you click The purpose of running this scenario in ALOHA and MARPLOT was to get an estimate of the concentration of chlorine to which the workmen were exposed Text Summary THREAT AT POINT Concentration Estimates at the point West 334 yards South 121 yards Max Concentration Outdoor 11 7 ppm Indoor 6 169 ppm 97 Chapter 3 Examples ALOHA was designed to give you ballpark estimates of source strength and dispersion It cannot give you completely accurate predictions for a real release because no model can account for every uncertainty For example ALOHA predicted that the workmen were exposed to a concentration of 11 7 ppm of chl
122. eat Zone Loc ERPG 1 50 ppm Show confidence lines only for longest threat zone C for each threat zone Cancel 59 Chapter 3 Examples You ll see ALOHA s threat zone plot ESEE oan a for this scenario showing three toxic idhe oox threat zones You want to know the downwind distance to the ERPG 2 level specified by the Local Emergency Planning Committee ALOHA estimates that the orange threat zone the ERPG 2 level will extend 281 yards downwind the exact value for this threat distance is displayed in the Text Summary Within this zone ground level benzene concentrations might exceed the ERPG 2 level At concentrations above the ERPG 2 level people could experience serious health effects or Apnea find their ability to escape to be MM gt 50 ppm rec a impaired if they are exposed for ee about an hour o Check the Text Summary for this release Text Summary SOURCE STRENGTH Leak from hole in vertical cylindrical tank Flammable chemical escaping from tank not burning Tank Diameter 4 feet Tank Length 5 32 feet Tank Volume 566 gallons Tank contains liquid Internal Temperature 86 F Chemical Mass in Tank 1 82 tons Tank is 166 full Circular Opening Diameter 6 inches Opening is 16 inches from tank bottom Ground Type Concrete Ground Temperature equal to ambient Max Puddle Diameter Unknown Release Duration 46 minutes Max Average Sustained Release Rate 77 2 pou
123. ect either e Use internal clock to use your computer s internal clock or e Set a constant time to set a specific time when you want a scenario to begin Type in the month day year hour and minute This option is useful for contingency planning or training exercises because you can set up scenarios to run at different times of the day and or year and therefore under different atmospheric conditions ALOHA uses the 24 hour time system in which time of day is indicated by four digits The first two digits indicate the hour 00 to 23 pa pec fe pra ne and the last two indicate the number of minutes past that hour 00 to 59 Each day begins at midnight 0000 and the last minute of each day is 2359 Under this system 6 00 a m is 0600 Input a constant date and time and 2 30 p m is 1430 Month Day Year Hour Minute 1 12 1 31 1900 0 23 0 59 Cancel Help Date and Time Options C Use internal clock Set a constant time 106 Chapter 4 Reference SetUp menu As you enter information into ALOHA about a release scenario you ll move on to the SetUp menu after you ve completed your work with the SiteData menu Choose items from this menu to select a chemical from ALOHA s chemical library describe weather conditions and explain how the chemical is escaping from containment You also can specify how you want ALOHA to predict the dispersion of the pollutant cloud in the atmosphere for dispersion scenarios tha
124. ed In such a case ALOHA will make Gaussian calculations but will alert you that you should try running the heavy gas model as well i Note This chemical may flash boil and or result in two phase flow Use both dispersion models to investigate its potential behavior Use Gaussian dispersion only Choose this option if you know that the escaping gas cloud is approximately neutrally buoyant about as dense as air ALOHA will use the Gaussian equation to predict the spread of the cloud Avoid using ALOHA s Gaussian model to predict how a large heavy gas cloud will disperse Large gas clouds that are denser than air heavy gases disperse in a very different way than this model would predict They are affected by gravity and other forces besides wind and turbulence As they move downwind they remain much lower to the ground than neutrally buoyant clouds and flow like water Ground level concentrations within such clouds may reach much higher levels at some locations than the Gaussian model would predict 148 Chapter 4 Reference 3 Use Heavy Gas dispersion only Choose this option if you know that the cloud is heavier or denser than air You will be alerted if ALOHA does not have enough property information to make heavy gas calculations for your selected chemical To see a list of the properties needed for heavy gas calculations see Table 4 1 on page 111 To view the property values in the library for your selected chemical ch
125. ed and air temperature This is because the environment within a large modern enclosed building is controlled and kept nearly constant regardless of weather conditions using a heating ventilating and air conditioning HVAC system The American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE recommends that air exchange rates for buildings be kept within the range of 0 5 to 1 0 complete changes per hour to maintain air quality If you know a building s air exchange rate the number of times per hour that the total air volume within the building is replaced type this number next to No of air changes You also can adjust this number to compare the effects of different air exchange rates on indoor infiltration of a pollutant gas When you specify single or double storied building type you also must indicate whether the building is sheltered or unsheltered Pollutant gases infiltrate more slowly into sheltered than unsheltered buildings of the same type Below is a decision aid for choosing between sheltered or unsheltered surroundings Surrounding Features Selection Choice If the buildings are surrounded by trees bushes or other buildings in Sheltered surroundings the direction from which the chemical cloud will be coming If the buildings are in an open space with nothing near them Unsheltered surroundings If you don t know about the surrounding features or if you are unsure Unsheltered
126. ed to it from an inert gas When liquefied propane or a similar chemical escapes from storage it can form a heavy gas cloud The cloud is heavy in part because it is initially cold and also because it consists of a two phase mixture The tiny aerosol droplets mixed into the cloud act to weigh the cloud down and make it denser and their evaporation acts to cool the cloud When ALOHA predicts that a liquefied gas will escape as a two phase flow it alerts you with a message on the Text Summary Note The chemical escaped as a mixture of gas and aerosol two phase flow When you use ALOHA to model a release from a tank of a liquefied gas such as propane generally ALOHA will predict that the substance will escape as a two phase flow if the tank is pressurized It treats ammonia and chlorine as special cases however because enough information about these chemicals is available to permit the use of more refined source strength calculations When there is only a small amount of material in a tank the hole in the tank is small or the tank pressure is low ALOHA predicts that these two chemicals will escape from storage as a pure gas rather than as a two phase flow 137 Chapter 4 Reference Tank Size and Orientation To model the release of a liquid or gas from a storage tank you must indicate both the size of the tank and its general shape which affects how it will drain Choose the most appropriate of three tank types Horizonta
127. edicts that outdoor concentration would exceed one LOC AEGL 2 only briefly but will exceed a lower LOC AEGL 1 for much longer The indoor concentration does not exceed any of the LOC values however it does approach the AEGL 1 LOC for a significant period of time At this level people inside the building may begin to experience notable discomfort irritation or other temporary effects Bear in mind that no LOC represents an exact line between hazardous and non hazardous conditions because people differ in their sensitivity to chemicals for example old sick or very young people may be more sensitive to chemicals than healthy adults and other hazards People who are more sensitive to the chemicals may experience more serious health effects than those predicted for the AEGL 1 level even though that level was not exceeded in the hour after the release Note ALOHA will place a blue crosshair mark on the threat zone plot to indicate the location where the hazard is evaluated If you have plotted the threat zones on a map in MARPLOT ALOHA will place the crosshair mark on the map as well 155 Chapter 4 Reference What if the doors and windows are open To estimate the rate at which pollutant gas could infiltrate into buildings ALOHA assumes that all doors and windows are closed If doors and or windows are open as they might be on a warm summer day concentrations might increase more rapidly and drop off sooner inside building
128. eed and direction may be very different from the rest of the area Place the SAM upwind of the source of a pollutant gas release so that you will not need to decontaminate it after use Choosing the correct port for receiving SAM data SAM data is transmitted to ALOHA through your computer s serial port On a Windows computer this is the COM1 COM2 COM3 or COM4 port On a Macintosh computer this is the modem port Choosing a radio frequency If you are using ALOHA within the U S you ll find that the rules for assigning and using radio frequencies are specific to your locality no national guidelines exist Check with the manufacturer of your SAM or with the government authority in your area that assigns radio frequencies if you want to be assigned a frequency that you can use to transmit SAM information to ALOHA This authority could be a local state or federal agency depending on your location Setting up ALOHA when you re using a SAM Check to be sure that your SAM is properly connected configured and turned on you ll need to check with the manufacturer if you have questions on how to do this Next in the SetUp menu point to Atmospheric then select SAM Station If you are using a Windows computer you will be asked to indicate the port to which the SAM station is connected Chemical Ctrl H Atmospheric gt User Input Ctr Calculation Options 123 Chapter 4 Reference You ll need to enter some informat
129. een and tell ALOHA that now the chemical is burning and it has formed a pool fire Begin by selecting the Tank source again In the SetUp menu point to Source then select Tank A Tank Size and Orientation dialog box appears Notice that all of your original information is already entered into the dialog box The dimensions of the tank have not changed so you can just click OK to move to the next screen Your original information is still correct on the Chemical State and Temperature and the Liquid Mass or Volume dialog boxes Click OK on each screen until the Type of Tank Failure dialog box appears Choose the Leaking tank chemical is burning and forms a pool fire option Click OK An Area and Type of Leak dialog box appears Type of Tank Failure Scenario Tank containing an unpressurized flammable liquid Type of Tank Failure C Leaking tank chemical is not burning and forms an evaporating puddle Leaking tank chemical is burning and forms a pool fire C BLEYE tank explodes and chemical burns in a fireball Potential hazards from chemical which is burning as it leaks from tank Thermal radiation from pool fire BLEVE if heat raises the internal tank temperature and causes the tank to fail Downwind toxic effects of fire byproducts cannot be modeled by ALOHA Cancel 61 Chapter 3 Examples 7 Your original information is still correct on the Area and Type of Leak Height of the Tank Openin
130. el the situation first as a pool fire and then rerun the scenario as a BLEVE to compare the size of the threat zones 24 Chapter 1 Welcome to ALOHA BLEVEs BLEVE stands for Boiling Liquid Expanding Vapor Explosion BLEVEs typically occur in closed storage tanks that contain a liquefied gas usually a gas that has been liquefied under pressure A gas can be liquefied by either cooling refrigerating it to a temperature below its boiling point or by storing it at a high pressure Although both flammable and nonflammable liquefied gases may be involved ina BLEVE ALOHA only models flammable liquid BLEVEs Propane is an example of a chemical that has been involved in many BLEVE accidents Most propane tanks at service stations contain liquid propane These tanks are neither insulated nor refrigerated so the tank contents are at ambient temperature Since the ambient temperature is almost always significantly above propane s boiling point of 43 7 F the tanks are highly pressurized A common BLEVE scenario happens when a container of liquefied gas is heated by fire increasing the pressure within the container until the tank ruptures and fails When the container fails the chemical is released in an explosion If the chemical is above its boiling point when the container fails some or all of the liquid will flash boil that is instantaneously become a gas If the chemical is flammable a burning gas cloud called a fireball may occur if
131. emical stored at ambient temperature C Chemical stored at 80 degrees So we 138 Chapter 4 Reference Next to enter the temperature within the tank either Click Chemical stored at ambient temperature if the chemical is stored at the temperature of the surrounding air you entered the air temperature when you entered atmospheric information or Enter the storage temperature in the tank temperature data field if the tank is at a different temperature and indicate its units Whether a liquid is stored in a tank at a temperature above or below its boiling point greatly affects how it will escape through a tank rupture or leaking valve If the liquid is stored below its boiling point it will flow out of the tank and form a puddle on the ground If the liquid is stored above its boiling point the pressure within the tank will be greater than atmospheric pressure When such a tank is punctured the liquefied gas contents may escape as a two phase mixture of gas and aerosol The rate of release can be significantly greater than the rate of release of an unpressurized liquid Liquid in a tank Whenever you indicate to ALOHA that a tank contains liquid by clicking Tank contains liquid when you are asked to identify chemical state you will need to identify the amount of chemical in the tank in any of four ways mass of chemical liquid volume percent full by volume or height of liquid level in the tank Choose to Type the mas
132. ent types of air dispersion models exist They range from simple equations that can be solved by hand to complex models that require massive amounts of input data and powerful computers The type of model appropriate for a particular use depends on the scale of the problem the level of detail available for input and required for output the background of the intended user and the time available to wait for the model computations to be completed ALOHA was designed with first responders in mind Its air dispersion model is intended to be used to estimate the areas near a short duration chemical release where key hazards toxicity flammability thermal radiation or overpressure may exceed user specified Levels of Concern LOCs Note If the released chemical is not flammable toxicity is the only air dispersion hazard modeled in ALOHA ALOHA is not intended for use with radioactive chemical releases nor is ALOHA intended to be used for permitting of stack gas or modeling chronic low level fugitive emissions Other models are designed to address larger scale and or air quality issues Turner and Bender 1986 Since most first responders do not have dispersion modeling backgrounds ALOHA has been designed to require input data that are either easily obtained or estimated at the scene of an accident ALOHA s on screen help can assist you in choosing inputs 15 Chapter 1 Welcome to ALOHA What is dispersion Dispersion is a term use
133. er specified CHEMICAL DATA Chemical Name PROPANE Molecular Weight 44 16 g mol TEEL 1 2106 ppm TEEL 2 2166 ppm TEEL 3 2166 ppm IDLH 2166 ppm LEL 26668 ppm UEL 95668 ppm Ambient Boiling Point 44 6 F Vapor Pressure at Ambient Temperature greater than 1 atm Ambient Saturation Concentration 1 666 606 ppm or 166 6 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 16 miles hour from 366 true at 16 meters Ground Roughness urban or forest Cloud Cover 16 tenths Air Temperature 76 F Stability Class D No Inversion Height Relative Humidity 67 SOURCE STRENGTH BLEVE of flammable liquid in horizontal cylindrical tank Tank Diameter 9 67 feet Tank Length 76 feet Tank Volume 33866 gallons Tank contains liquid Internal Storage Temperature 76 F Chemical Mass in Tank 76 1 tons Tank is 166 full Percentage of Tank Mass in Fireball 166 Fireball Diameter 253 yards Burn Duration 14 seconds Choosing LOCs and creating a threat zone plot for a BLEVE 1 Choose Threat Zone from the Thermal Radiation Level of Concern Display menu A Thermal Select Thermal Radiation Level of Concern Radiation Level of Concern Red Threat Zone dialog box appears Loc PLASA E a ee GA E ot x 2 You want to know the thermal radiation threat for a BLEVE Keep ALOHA s default LOCs Orange Threat Zone and click OK ALOHA will Loc display a threat zone plot for this release Yellow Threat Zone Loc 2 0 kW sq m pain within 60 sec X
134. es Data DIPPR database 107 Chapter 4 Reference Selecting a pure chemical To choose a pure chemical locate its name in the chemical list Chemical names appear in alphabetical order in the list with prefixes such as n tert or 1 2 ignored To navigate quickly through the list type the first one or two letters of the name then scroll up or down until you see the name of the chemical that you wish to select Double click on the name or click once on the name then click Select to select it Once you have selected a chemical you ll see some of its most important properties listed in the Text Summary window Chemical Information Pure Chemicals View C Solutions Select CARBON TETRAFLUORIDE a i CARBONYL FLUORIDE CARBONYL SULFIDE CHLORAMINE CHLORINE Add Cancel CHLORINE DIOXIDE CHLORINE PENTAFLUORIDE CHLORINE TRIFLUORIDE CHLOROACETONE CHLOROACETONITRILE CHLOROACETYL CHLORIDE CHLOROBENZENE P CHLOROBENZOTRIFLUORIDE Selecting a chemical solution To choose one of ALOHA s chemical solutions click on the Solutions option to display the list of solutions Double click on the name or click once on the name then click Select to select it Type in its percent by weight in the Solution Strength box ALOHA shows you the allowable range Once you have selected a solution you ll see some of its most important properties listed in the Text Summary window Chemical Information
135. es passively away from the release point without rising substantially upwards as a gas emitted from a heated or burning source may do or slumping downward towards the ground as a heavy gas may do If you enter a source height greater than zero but your selected chemical is a heavy gas ALOHA will alert you that it must use a source height of zero to model the release Although the source height that you entered appears in the Text Summary ALOHA assumes the height to be zero when making its dispersion computations If you are not sure of the source height bear in mind that a ground level release is a more conservative choice than an elevated release ALOHA will predict a longer threat zone for a ground level release Puddle Source In the SetUp menu point to Source then select Puddle Choose the Puddle source option to model a liquid that has already spilled and formed a puddle on the ground i e it is not changing in area ALOHA can model the puddle either as an evaporating puddle or if the chemical is flammable as a pool fire Note If liquid is continuing to leak from a tank and spill into a puddle so that the puddle s area and volume are increasing choose the Tank source option instead Chemical Ctrl H Atmospheric gt i Puddle Ctrl U Calculation Options Tark ae Le Gas Pipeline Ctrl I 132 Chapter 4 Reference Type of Puddle When you use the Puddle source with a flammable chemical ALOHA will a
136. eseacsdanncxssesssveusnaveraaeeondceudee E 28 Very stable atmospheric conditions 0 eee eee ceeeeeseeceeeceseeeseeeeaeecsaeenseenees 28 Wind shifts and terrain steering effects 2 0 0 ee eeeeeeeeeeeseeeceeeeeceteeeeneeeees 29 Concentration patChimess vcsi jcadiauevsisatessrccassaccsdanceveneddscacedon spasaavasensaccosenee 30 Effects that are not modeled n2j uea Chapala Guanes de 31 Byproducts from fires explosions or chemical reactions eee 31 Particulates eienenn ne A Aa Oe aes ee Ee aa a E 31 Chemical Mixtures 233 24 442 4 conic Bede a i a ee 31 TOS OU ANN gfestty ces aerate cei ata nel ese oe sues Neer omits ee aR tt ce 31 Hazardous frasrients s vcevcssisascaasscvciealepeactassnczevascevadeadooraceeadeceentsorsatisaees 31 Chapter 2 Learning the Basics 0 cece wee cece cece wees eecees 33 Guided tOUr mnnn GA een lana inane 33 Deseribing the tine and place case psa a dialed etait ERNA 34 CHOOSING A CHEMICAL Seeria pated devs cae ated gnasbontocdsaad shes ea ei 36 Describing the Weather scicsccisjsieessepeatatiassaiei nina E E A T E Ei 36 Deseribing the r leaseicocenni son dae ae E E etek eons ETRA 38 Checking the Calculation and Display Options settings eeceeeeeeceeceeeeeeeeeeteeeesteeeeeaes 42 Creating a threat Zone plot x sicisccissescedsi neriti AE os aE a jedetasa dan R aa veces 43 Determining threat levels at a specific LOCAtION ee eee eeeceeeeeeeecneecneeeeeeeeaeeceaeenseensees 46 Ex
137. f the stored liquid would turn instantly to vapor so that a mixture of liquid droplets and vapor a two phase flow would be released to the atmosphere ALOHA s Tank source release calculations account for these processes but the Direct source option does not Since you don t have the necessary information to run the Tank option you ll use the Direct source calculations as the best approximation that you can make recognizing that ALOHA will treat this release as a steady flow of gas from the tank instead of a time dependent release a release where rate varies over time Click OK 89 Chapter 3 Examples The source strength information that you have entered into ALOHA and the results of ALOHA s computations appear in the Text Summary Text Summary SOURCE STRENGTH Direct Source 456 pounds Source Height 6 Release Duration 1 minute Release Rate 7 5 pounds sec Total Amount Released 456 pounds Note This chemical may flash boil and or result in two phase flow Choosing LOCs and creating a threat zone plot Now that you ve entered all of the release information you can display the results of ALOHA s threat zone calculations 1 Choose Threat Zone from the Display menu A Toxic Level of Concern dialog box appears 2 ALOHA uses 60 minute AEGLs Acute Exposure Guideline Levels as the default Levels of Concern LOCs for chlorine Keep the default LOCs and check that Show confidence lines only for the longest threat zon
138. g and Maximum Puddle Size dialog boxes Click OK on each screen The source strength information that you have entered and the results of ALOHA s source strength calculations appear in the Text Summary ALOHA estimates that the puddle burns for about two minutes and that the Maximum Burn Rate is 1 610 pounds per minute Notice that ALOHA estimates that the puddle reached a maximum diameter of 15 0 yards which is smaller than the 21 7 yards estimated for the evaporating puddle because the chemical is being consumed in the fire before the puddle can spread to the larger diameter Text Summary SITE DATA Location BATON ROUGE LOUISIANA Building Air Exchanges Per Hour 6 58 unsheltered single storied Time August 26 2066 2236 hours CDT user specified CHEMICAL DATA Chemical Name BENZENE Molecular Weight 78 11 g mol ERPG 1 56 ppm ERPG 2 156 ppm ERPG 3 1666 ppm IDLH 566 ppm LEL 12666 ppm UEL 86666 ppm Carcinogenic risk see CAMEO Ambient Boiling Point 176 1 F Vapor Pressure at Ambient Temperature 6 13 atm Ambient Saturation Concentration 134 835 ppm or 13 5 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 7 miles hour from SW at 16 meters Ground Roughness open country Cloud Cover 7 tenths Air Temperature 86 F Stability Class D No Inversion Height Relative Humidity 75 SOURCE STRENGTH Leak from hole in vertical cylindrical tank Flammable chemical is burning as it escapes from tank Tank Diameter 4 feet Tank
139. g garage is a partially confined space ALOHA does not model partially or completely confined vapor clouds 27 Chapter 1 Welcome to ALOHA ALOHA s limitations Like any model ALOHA cannot be more accurate than the information you give it to work with so it is important to enter the most accurate information If you are unsure of a value you should choose a value that would give the worst case scenario or run multiple scenarios and compare the results Consult the on screen help or the Reference chapter if you are unsure of what choice to make Additionally ALOHA s models use atmospheric information to estimate the spread of the chemical release If any of the atmospheric conditions e g wind speed change substantially during a response you should correct the inputs and create a new threat zone plot because the old plot may no longer be accurate Even when you can provide accurate input information ALOHA s results can be unreliable under some conditions and there are some effects that ALOHA doesn t model at all Conditions that can produce unreliable results ALOHA s results can be unreliable when the following conditions exist e Very low wind speeds e Very stable atmospheric conditions e Wind shifts and terrain steering effects or e Concentration patchiness particularly near the release source Very low wind speeds ALOHA s threat zones are accurate if the wind direction does not change from the value that you entered
140. gas spreads out into the atmosphere mixing with the air and eventually becoming diluted to below hazardous levels 173 Glossary Eddies ERPGs Exponential notation Fireball Flammable Parcels of air of various sizes that leave their normal position within an otherwise orderly smooth flow For example air that encounters an obstacle must go over or around it This change in the direction of air flow often causes swirls of air or eddies to tumble off the back of the obstacle Impediments to airflow ranging from simple friction grass to larger obstacles buildings can cause eddies in a variety of sizes to form The Emergency Response Planning Guidelines ERPGs are Toxic Levels of Concern LOCs that you can use in ALOHA to predict the area where a toxic gas concentration might be high enough to harm people The ERPGs were developed by the ERPG committee of the American Industrial Hygiene Association The ERPGs were developed as planning guidelines to anticipate human adverse health effects caused by exposure to toxic chemicals The ERPGs are three tiered guidelines with one common denominator a 1 hour contact duration Each guideline identifies the substance its chemical and structural properties animal toxicology data human experience existing exposure guidelines the rationale behind the selected value and a list of references ERPG Web site http www aiha org ALOHA displays its results in exponentia
141. ges direction and speed significantly altering a cloud s shape and movement as seen in Figure 1 4 Through streets bordered by large buildings can generate a street canyon wind pattern that constrains and funnels a dispersing cloud ALOHA ignores these effects when it produces a threat zone plot the threat zone will appear to go right over or through obstacles such as buildings Consider the effects of terrain on wind flow whenever you are interpreting ALOHA results Figure 1 4 Small scale variations in wind direction 29 Chapter 1 Welcome to ALOHA Because the wind is likely to shift in direction and change speed over both distance and time limits have been placed on ALOHA s output ALOHA will not make predictions for more than an hour after a release begins or for distances more than 10 kilometers 6 2 miles from the release point it truncates threat zones that are longer than 10 kilometers ALOHA s 1 hour time cutoff exists because wind shifts direction and changes speed frequently One reason for the 10 kilometer cutoff for ALOHA threat zone length is that we don t know what the wind speed and direction are 10 kilometers away and can t assume that they are the same as those at the point where a chemical is being released If ALOHA has incorrect values for wind speed and direction it can t correctly estimate threat zone size or location Concentration patchiness No one can predict the gas concentration at any particular
142. gth and direction of travel For example if many buildings surround the explosion site expect the actual overpressure threat zone to be somewhat smaller than ALOHA predicts But at the same time more hazardous fragments could be generated as the blast causes structural damage to those buildings 21 Chapter 1 Welcome to ALOHA Overpressure Levels of Concern An Overpressure Level of Concern LOC is a threshold level of pressure from a blast wave usually the pressure above which a hazard may exist When you run a vapor cloud explosion scenario ALOHA will suggest three default LOC values ALOHA uses three threshold values to create the default threat zones e Red 8 0 psi destruction of buildings e Orange 3 5 psi serious injury likely and e Yellow 1 0 psi shatters glass ALOHA s default overpressure values are based on a review of several widely accepted sources for this topic e g American Institute of Chemical Engineers 1994 Federal Emergency Management Agency et al 1988 and Lees 2001 If you choose to set your own LOC values consider Table 1 3 Lees 1980 which relates overpressure values to the structural and physiological effects produced Table 1 3 Explosion overpressure damage estimates ONEE DES ine Expected Damage psig 0 04 Loud noise 143 dB sonic boom glass failure 0 15 Typical pressure for glass failure 0 40 Limited minor st
143. han unsheltered choose Building Type from the SiteData menu again click Unsheltered surroundings then click OK When you are sure that the Text Summary information is correct you re ready to move on to the next steps 41 Chapter 2 Learning the Basics Checking the Calculation and Display Options settings Unless you specifically change its default setting ALOHA uses information about the properties of the chemical and the amount of chemical released to choose whether to make Gaussian or heavy gas dispersion computations Check to be sure that ALOHA is set to this default 1 2 Select Calculation Options from the SetUp menu A Calculation Options dialog box appears Check to be sure that Let ALOHA decide select this if unsure is selected Click OK Calculation Options SetUp Select the Spreading Algorithm for Downwind Dispersion Chemical Ctrl H i G Hen Atmospheric gt Let ALOHA decide select this if unsure C Use Gaussian dispersion only Source gt A C Use Heavy Gas dispersion only Calculation Options Cancel Select Display Options from the Display menu A Display Options dialog box appears Select English units and ALOHA s computation results will be displayed in those units When running ALOHA you can choose either type of units but for this example English units have been selected Click OK Threat Zone Ctrl F Display Options Select Output Units Text Summary Ctrl K
144. he Text Summary When you select a chemical such as benzene which has been identified as a confirmed potential or suspected carcinogen a notation Carcinogenic risk see CAMEO will appear in the Text Summary When you select a chemical for which little information is available ALOHA displays the following note in the Text Summary Not enough chemical data to use Heavy Gas option This note alerts you that although the chemical s molecular weight is heavier than 29 kilograms per kilomole the average molecular weight of air so that it may behave like a heavy gas ALOHA will have to use Gaussian dispersion calculations to model its behavior in the atmosphere unless you add additional property information Text Summary DE x SITE DATA Location SEATTLE WASHINGTON Building Air Exchanges Per Hour 6 58 unsheltered single storied Time August 26 2666 2236 hours PDT user specified CHEMICAL DATA Chemical Name SARIN Molecular Weight 146 11 g mol AEGL 1 66 min 4 8e 64 ppm AEGL 2 66 min 6 666 ppm AEGL 3 66 min 6 622 ppm Normal Boiling Point 297 6 F Note Not enough chemical data to use Heavy Gas option Chemical data The chemical library includes information about the physical properties of each ALOHA chemical It also includes depending on the chemical values for AEGLs 60 minute ERPGs TEELs IDLH UEL and LEL You can add your own toxic LOC for any pure chemical to ALOHA s chemical library ALOHA will automat
145. he area between the accident site and the injured workmen is flat and free of obstacles so select the Open Country ground roughness option The sky is one third covered Under Select Cloud Cover choose the fourth option from the left the option between the partly cloudy and clear options Notice that ALOHA has filled in a value of 3 Click OK The second Atmospheric Options dialog box appears Atmospheric Options Wind Speed is 6 C knots mph meters sec Help Wind is from E Enter degrees true or text e g ESE Measurement Height above groundis Help 3 g a A OR enter value 3 feet meters Ground Roughness is Help Open Country A i C Urban or Forest OR Input Roughness Zo C Open Water Select Cloud Cover complete partly cover cloudy Help OR enter value 3 0 10 C clear r ce Cancel 87 Chapter 3 Examples 6 The air temperature is 72 F Type Atmospheric Options 2 mos z 72 in the air temperature box Air Temperature is 72 Degrees F CC Help Stability Classis Help C 4 CB C G C Override Inversion Height Options are Help then select F 7 ALOHA uses the wind speed cloud cover and date and time i E feet information that you ve entered to RN EE E A sameter automatically select atmospheric Select Humidity Help Stability Class C k 4 8 There is no low level inversion s C OR entervalue gg 7 medium dry 0 10
146. he best EastWest North South method to choose if you wish to monitor the Meton ee ne expected hazard at the school and you are using a Y the north south distance SAM to track wind speed and direction in fram the source feet ALOHA If the wind shifts direction the results InputX C East West 100 2 ees displayed by ALOHA may change depending on InputY North C South 400 C meters whether or not the shift in wind direction moves C kilometers the pollutant cloud closer to the school or farther Cancel Haly away from it Using relative downwind and crosswind coordinates Choose this option when you wish Thermal Radiation Location Specify the location at which you want to evaluate the to know the hazard expected at a position that can thermal radiation over time best be d ibed in t fitsd ind and Relative Coordinates Evaluation est be described in terms of its downwind an Dowiivindereaswindl Point Oo crosswind distance from the release point For eg eee A ie lect example suppose that you have estimated the EastWest North South straight line distance between the site of a release Input X the downwind Source p distance from the source and and a nearby hospital to be a half mile At the Y the perpendicular distance moment the wind is not blowing the chemical ote oense sae z ga A A ards cloud directly towards the hospital but the wind is Input eee omneindialataneceijo 5 ae variable in direction
147. he library Modifying a chemical entry in the library To modify information about a chemical first select Chemical from the SetUp menu Select the name of the chemical in the dialog box that appears then click Modify Click on the name of each property that you are adding or modifying in the scrolling list or click Next Field until you ve highlighted the property name Type property values in the corresponding boxes or modify existing values and modify units if necessary 112 Chapter 4 Reference You ll find that you cannot modify all property values for ALOHA chemicals already included in the library Values that you cannot modify and their units appear dimmed These are values that ALOHA calculates internally using either values for the chemical s critical properties molecular weight boiling point critical temperature and critical pressure or information from the DIPPR database If you would like to use your own property values for an ALOHA chemical add the chemical using a slightly different name such as CHLORINE 2 and type your own values in the new property boxes When you re finished making your modifications click OK to add them permanently to ALOHA s library To avoid making permanent changes to the library click Cancel Deleting a chemical from the library To permanently delete a chemical from ALOHA s library select Chemical from the SetUp menu Select the name of the chemical in the dialog box that appears
148. he pressure within this section of pipe declines as gas is released release rate drops over time and the release continues only until the finite length of pipe is emptied ALOHA cannot model gas release from a pipe that has broken in the middle and is leaking from both broken ends Pipe source inputs To describe a Gas Pipeline release to ALOHA type the pipe diameter and length indicate whether the pipe is connected to a reservoir indicate whether the inner pipe surface is smooth or rough type pipe pressure and temperature and type the area of the hole if the pipe is of finite length Pipe diameter and length Use the inner diameter of the pipe The pipe length must be at least 200 times the diameter of the pipe Pipe connection Indicate whether the pipe is connected at its unbroken end to a large reservoir infinite tank source or is closed off Pipe roughness Degree of roughness of the inner surface of the pipe A smooth pipe would be for example a new metal glass or plastic pipe A rough pipe would be for example a metal pipe with a rusted inner surface or a pipe that has been corroded on the inside by the chemicals it carries Rough texture causes turbulence which reduces the flow rate of the gas in the pipe A gas will flow more slowly through a rough pipe than through a smooth pipe Gas Pipeline Input Input pipe diameter 12 inches cm Diameter is Input pipe length Pipe length is 1212 ft
149. hoose Calculation Options from the SetUp menu to select the type of dispersion calculation used Calculation Options SetUp Select the Spreading Algorithm for Downwind Dispersion Chemical Ctrl H heri gt Let ALOHA decide select this if unsure Atmospheric C Use Gaussian dispersion only Source gt C Use Heavy Gas dispersion only Calculation Options Cancel You can choose from among three dispersion calculation options 1 Let ALOHA decide When you select this option ALOHA automatically chooses whether to predict the dispersion of a chemical as a Gaussian neutrally buoyant or heavy gas release It bases this choice mainly on molecular weight size of the release and temperature of the gas cloud By default this option remains selected unless you choose a different option When Let ALOHA decide is selected if ALOHA s chemical library does not include values for all physical properties of your selected chemical necessary to make heavy gas dispersion calculations ALOHA will use Gaussian dispersion calculations to predict threat zone size When a chemical with a molecular weight less than that of air has been stored at a low temperature or under high pressure it can behave like a heavy gas ammonia is an example of such a chemical If you have chosen one of these chemicals and have chosen the Direct source option ALOHA may not have enough information about the release to determine whether a heavy gas could be form
150. ht Cloud Cover Meters per Knots Miles per Strong Moderate Slight gt 50 lt 50 second hour lt 2 lt 3 9 lt 4 5 A A B B E F 2 3 3 9 5 8 4 5 6 7 A B B C E F 3 5 5 8 9 7 6 7 11 2 B B C C D E 5 6 9 7 11 7 11 2 13 4 C C D D D D gt 6 gt 11 7 gt 13 4 C D D D D Note Stability is D for completely overcast conditions during day or night Note This table is for releases over land If the release occurs over water the stability class will be either D or E Wind reference height is 10 meters Strong solar radiation corresponds to clear skies with the sun high in the sky solar angle greater than 60 degrees Slight solar radiation corresponds to clear skies with the sun low in the sky solar angle between 15 and 35 degrees You can click Override to change ALOHA s stability class choice and choose any of the six stability classes You should do this however only if you are sure that a special circumstance causes the best choice for stability class to be different from the choice made by ALOHA For example the atmosphere above a snow covered landscape is typically more stable than would be expected for a given combination of wind speed cloud cover and time of day If you are modeling a release over snow covered ground then you might want to choose a more stable class than ALOHA chooses for you Additionally some organizations may require users to model all scenarios using a single scenario c
151. ically use your LOC as the default for the selected chemical The ALOHA library contains information from two sources When available physical property values were obtained from a chemical database compiled by the Design Institute for Physical Properties Data DIPPR known as the DIPPR database Other values were obtained from the chemical database included in the Computer Aided Management of Emergency Operations CAMEO hazardous chemical information system developed by the U S Environmental Protection Agency and the National Oceanic and Atmospheric Administration 110 Chapter 4 Reference ALOHA uses information from the library to model the physical behavior of a chemical that you have selected For example once ALOHA knows the temperature within a tank it can use library information to estimate the vapor pressure density and other properties of the chemical stored in the tank You only need the name of a chemical and its molecular weight to run the simplest ALOHA scenario a toxic gas dispersion using a Direct source and the Gaussian dispersion model However ALOHA s more complex calculations require information about other properties of the chemical Check Table 4 1 for the property information needed for each source and dispersion model option You do not need to add a value for liquid density because ALOHA estimates this property from other information that you enter Table 4 1 Properties needed to use each ALOHA source
152. ies needed 111 Help on screen 14 humidity 121 I IDLH 178 ignition sources common 19 ignition time 150 ignition type 151 indoor pollutant concentration 105 155 infiltration rate 105 instantaneous release 131 inversion 120 J jet fire 24 191 Index L latitude 102 Level of Concern LOC default toxic LOC 150 in Text Summary 110 overpressure 22 thermal radiation 20 threat zone 150 toxic hierarchy 110 liquefied gas 137 179 Location menu item adding a non U S location 103 adding a U S location 102 CityLib 101 deleting a location 104 modifying a location 104 selecting a location 101 sun angle 101 longitude 102 Lower Explosive Limit LEL 19 26 Lower Flammable Limit LFL 26 low level inversion 121 M MARPLOT menu 160 threat zone 161 troubleshooting SAM 165 Set Source Point 165 threat zone 165 using 160 Max Average Sustained Release Rate 130 Max Burn Rate 130 melting point 175 Metric units 158 N near field patchiness 30 neutrally buoyant gas 16 17 New menu item 99 O office building enclosed 105 open country ground roughness 116 Open menu item planning mode 99 response mode 99 saved file 99 open water ground roughness 116 output units 158 overpressure damage table 22 definition of 180 explanation of 21 Levels of Concern 22 P partial pressure 180 particulates 181 parts per billion ppb 181 parts pe
153. ike a building can impede the flame front so they should not be considered obstacles for the purposes of congestion Greater turbulence allows the flame front to accelerate thereby generating a more powerful blast wave i e greater overpressure 151 Chapter 4 Reference ALOHA uses two congestion levels congested and uncongested Generally a congested zone has so many closely spaced obstacles that it is difficult or impossible to walk through it It is uncommon for this level of congestion to be found throughout the entire vapor cloud However pipe racks in industrial facilities and some forested areas where the trees and branches are closely spaced may be characterized as congested areas Uncongested zones include parking lots open fields suburban neighborhoods and most urban environments Choose the level of congestion congested or uncongested in the flammable area of the vapor cloud that is the part of the vapor cloud where the concentration is between the LEL and UEL If there is more than one congestion level in the flammable area of the vapor cloud choose the level that best represents the majority of the area Click OK An Overpressure Level of Concern dialog box appears Threat zone plot Once you have entered all necessary information about a release and chosen an LOC ALOHA will display a threat zone plot based on the LOC s that you specified If three LOCs are chosen ALOHA will display the threat zones in red
154. in the tank propane select Chemical from the SetUp menu A Chemical Information dialog box appears with a list of the chemicals in ALOHA s chemical library 8 Select Pure Chemicals at the top of the window this should be the default Find PROPANE in the list quickly type the characters pr to locate propane more rapidly in the list click on this name then click Select Entering weather information Chemical Information View Pure Chemicals C Solutions Cancel PIPERIDINE PROPADIENE PROPANE N PROPANOLAMINE N PROPANOL Add PROPARGYL ALCOHOL BETA PROPIOLACTONE PROPIONALDEHYDE PROPIONIC ACID PROPIONIC ANHYDRIDE PROPIONITRILE PROPIONITRILE 3 CHLORO PROPIONYL CHLORIDE Now that you ve selected the location time and chemical you must provide information about weather conditions and ground roughness 1 Inthe SetUp menu point to Atmospheric then select User Input The first Atmospheric Options dialog box appears 2 The wind is travelling from 360 at a speed of 10 miles per hour Type 10 in the wind speed box then select mph Type 360 in the wind direction box 3 The wind conditions are measured at a height of 10 meters Select the tower icon in the Measurement Height section Notice that ALOHA has filled in a value of 10 meters 4 The area surrounding the derailed cars is highly industrialized Select the Urban or Forest ground roughness option 5 The sky is complete
155. ine in the water treatment process these tanks are 2 5 feet in diameter and 6 8 feet long The highest risk operation at the plant is the changing of chlorine tanks This operation is done only during daytime hours At 2 30 p m on June 25 2006 while being moved into the building a single container begins to leak through a valve located in the center of one end this valve is one half inch in diameter The tank contains one ton of chlorine when it begins to leak Fire and explosion scenarios This tutorial chapter will give you a solid understanding of how to move through the ALOHA menus and enter scenario information However this tutorial only goes through a toxic gas dispersion scenario If you plan on using ALOHA to run fire and explosion scenarios you should also review the fire and explosion scenarios in the Examples chapter Local meteorologists at NOAA s National Weather Service Weather Forecast Office have provided the weather conditions at Sioux Falls These conditions are a wind speed of 5 miles per hour from the south measured at a height of 10 meters sky three tenths covered air temperature of 72 F and 50 percent relative humidity There is no low level inversion You ll use ALOHA to assess the potential hazard by estimating e The threat zones representing the areas downwind of the release that may be at risk and e The predicted chlorine concentrations at the Central Valley Elementary School located abou
156. information In some cases it cannot so it asks you to reenter information about the source For example by increasing air temperature you may cause a tank to be filled to more than 100 percent of capacity or a puddle s temperature to increase above its boiling point In such cases you must enter new source information to resolve the problem Before ALOHA can place a threat zone on your MARPLOT map a threat zone plot needs to be displayed in ALOHA To solve your problem in ALOHA choose Threat Zone from the Display menu then return to MARPLOT You should now see the threat zone on your map To delete a threat zone remaining on a map after a crash delete the entire ALOHA layer open the map again in MARPLOT choose Layer List from MARPLOT s List menu click on the lock icon for the ALOHA layer to unlock the layer then click Delete while the ALOHA layer is highlighted in the layer list A new ALOHA layer will be added next time you plot a threat zone on the map Whenever you bring MARPLOT forward so that its windows are in front of ALOHA s windows you ll halt data transmission from the SAM to ALOHA Bring ALOHA forward to update the weather data and threat zone 165 Chapter 5 Troubleshooting We have two computers in our office that Individual computers can come up with different sometimes give different answers for the same answers when they make the same calculations ALOHA scenario In particular different comp
157. instant downwind of a release with certainty because they result partly from random chance Instead ALOHA shows you concentration values that represent averages for time periods of several minutes it uses the laws of probability as well as meteorologists knowledge of the atmosphere to do this ALOHA predicts that average concentrations will be highest near the release point and along the centerline of any pollutant cloud and will drop off smoothly and gradually in the downwind and crosswind directions However especially near the source of a release wind eddies push a cloud unpredictably about causing gas concentrations at any moment to be high in one location and low in another This kind of movement is familiar to anyone who has tried to toast marshmallows over a campfire like the one in Figure 1 5 no matter where you sit the smoke from the fire always seems to come straight towards you Meanwhile the average concentrations are likely to behave approximately as ALOHA predicts As the cloud moves downwind from the release point these eddies shift and spread the cloud evening out concentrations within the cloud so that they become more similar to ALOHA s predictions Figure 1 5 Concentration patchiness close to the source 30 Chapter 1 Welcome to ALOHA Effects that are not modeled ALOHA doesn t account for the effects of e Byproducts from fires explosions or chemical reactions e Particulates e Chemical mixture
158. int Once you have displayed a hazard toxicity flammability thermal radiation or overpressure on a threat zone plot you can use the Threat at Point option to obtain specific information about the hazard at a point of interest such as a school or hospital in or around the threat zones You can find the threat at a point by either e Selecting Threat at Point from the Display menu or e Double clicking on a location on the threat zone plot Note If ALOHA was unable to generate a Threat Zone plot you can still look at the threat at a point by selecting Threat at Point from the Display menu If you select Threat at Point from the Display menu a dialog box will appear and you can define the point where you would like to obtain a threat estimate using either of two types of location coordinates fixed or relative coordinates Your choice of coordinates will affect the information ALOHA will present to you if the wind changes direction whether you re using a SAM or you manually enter a new value 153 Chapter 4 Reference Using fixed east west and north south coordinates Choose this option if you wish to Thermal Radiation Location Specify the location at which you want to evaluate the know the hazard expected at a specific thermal radiation over time geographical location This could be for example a AE z eni a school 100 yards to the west and 400 yards to the eee ae WE north of the release location This is t
159. into a building ALOHA assumes that all doors and windows are closed Whether you specify building type to be a a single or double storied building or b an enclosed office building makes a big difference in how ALOHA chooses an exchange rate value For single and double storied buildings ALOHA accounts for the effects of wind speed and temperature to compute air exchange rate ALOHA expects a building s air exchange rate to increase if the wind speed increases because a faster wind exerts more force to push air through the small openings in a building s walls The degree of difference between indoor and outdoor air temperature also affects ALOHA s air exchange rate estimate ALOHA assumes the temperature within the building to be 68 F or 20 C The greater the temperature difference the higher the air exchange rate regardless of whether the air within the building is warmer or cooler than the outside air this is because air masses of different temperatures have different pressures and pressure differences stimulate air movement The higher a building s air exchange rate the faster the concentration of a toxic gas is predicted to rise within the building To estimate exchange rate ALOHA assumes that single and double storied buildings are about as leaky as typical North American houses that have been studied by researchers Wilson 1987 For enclosed office buildings ALOHA uses a constant air exchange rate of 0 5 regardless of wind spe
160. ion concentration it has a strong ability to displace air and the concentration of the chemical s vapor in the air above the liquid will be high If it s low the vapor concentration will be low This property changes with temperature a liquid at a higher temperature will have a higher ambient saturation concentration The ambient saturation concentration of a gas is 1 000 000 parts per million or 100 percent ALOHA displays ambient saturation concentration because it can sometimes be useful to you to compare it with a threshold concentration of concern such as a Lower Explosive Limit 109 Chapter 4 Reference Level of Concern LOC An LOC is a threshold value of a hazard toxicity flammability thermal radiation or overpressure the LOC is usually the value above which a threat to people or property may exist A list of standard LOCs will appear on the Text Summary screen including AEGLs ERPGs TEELs IDLH UEL and LEL For toxicity there are often several different standard LOC values to choose from AEGLs ERPGs TEELs and IDLH all relate to toxic thresholds ALOHA uses the following hierarchy to choose a default toxic LOC 1 60 minute AEGL 2 ERPG 3 TEEL and 4 IDLH For AEGLs ERPGs and TEELs the rank number increases with the hazard level so that AEGL 3 is more hazardous than AEGL 1 Typically the 3 values are used for the red threat zones which represent the worst hazard ALOHA sometimes places notes in t
161. ion about environmental conditions e Ifa low level inversion is present type in the height of the inversion layer and select appropriate units If there is no inversion be sure that No Inversion is selected e Indicate the ground roughness in the area downwind of the release point e Specify the station height the height of the instruments above the ground e Indicate the amount of cloud cover in tenths e Enter a value for relative humidity as a percentage Even if your SAM can measure relative humidity you ll need to enter this value manually into ALOHA User Input for SAM Unit Inversion Height Options are Help No Inversion Select Cloud Cover Help G ce Inversion Present Height is reet ra c C C meters Ground Roughness is Help C E C ORC entervalue 3 eo Count complete partly clear 0 10 pen woun y OR Input Roughness Zo cover cloudy Cloud Cover and Humidity C Urban or Forest C Open Water Select Humidity Help c a C ORC entervalue 50 Gi a is OR entervalue 3 feet wet medium dry 0 100 meters Cancel Cancel Station Height above ground is Help He c ALOHA will not allow you to choose items from the Source menu until the SAM has been collecting data for at least 5 minutes SAM Options After you click OK on the Cloud Cover and Humidity dialog box you ll see a new menu SAM Options to the right of ALOHA s Sharing menu You need not choose any items in this menu to u
162. iting it ALOHA os ee Fap aan aah cae ade Gul at a8 bath ae g sen jets eiae bees 48 Chapter 3 Examples sos 55 5 4 8 ees a als is ibs ooo asin Ose eos ad ees Sesh RS 49 Example 1 A Tank Source Puddle and Pool Fire cece ceesesseecsseceseeeeeeesaecnseesseeeenees 49 Choosing a location and a Chemical 0 cceeccecescceceseeceeececeeceeceeeeeeseeeesaeeeeneeeenaees 49 Entering weather niormation ccewin eet ela ene eee ee 51 Describing 16 Tele Ase ninesi na e ea i arinei 53 Checking the Calculation and Display Options Settings eeceeeeceeeeeeeeeteeeees 58 Choosing LOCs and creating a threat zone plot sseseseeseeeessseereeserssesreeseesresrresee 58 Modeling a second scenario pool fire sssssesssesesseeesseesserssersseresseeessresseesseeesees 61 Choosing LOCs and creating a threat zone plot for the pool fire eee 63 Table of Contents Example 2 A Tank Source Multiple Scenarios eee eeceeeeceeseeceseceseeeeeeeeseeceeeeseeeeneees 66 Choosing a location and a Chemical 000 ceecceeesccecsseeceeececeeececseeeeeseeeesaeeeeneeeesaees 66 Entering weather information 202ii 22 dessa Geeseiiedeniaenadecieesdagseeiee eieteneett 68 Describing the release sarc esol ee telnet ne tee cee alg Rete 70 Choosing LOCs and creating a threat zone plot fora BLEVE eeeeeeeeeees T2 Modeling a second scenario flash fire or vapor cloud explosion ceeeeeeeee 74 Choosing LOCs and creating threat zo
163. l cylinder Tank Size and Orientation e Vertical upright cylinder or Select tank type and orientation e Sphere 3 Vertical cylinder Next enter the tank s dimensions If it ee is acylinder enter any two of the A following three values a diameter b length or c volume If it is a Enter two of three values sphere enter either the tank s diameter 2 5 i A Gf r diameter or its volume ALOHA will length fes aa meire diameter compute and display values for the S l o remaining dimensions Volume refers a G Ea E ania to the total volume of the tank rather i a Cancel Hel than the volume of chemical within E ara the tank Chemical State and Temperature Next you ll need to specify the state and temperature of the chemical in the tank How the chemical is stored affects how the chemical may escape from the tank as a pure gas an unpressurized liquid or a liquefied gas Click the button corresponding to one of the following options Tank contains liquid Choose this option if there is any liquid in the tank even if it s just a small amount e Tank contains gas only Choose this option if you know that the tank contains only gas with no liquid present e Unknown Choose this option if you don t know the chemicals state Chemical State and Temperature Enter state of the chemical Tank contains liquid Tank contains gas only C Unknown Enter the temperature within the tank Help Ch
164. l notation whenever numbers are too large to display in decimal notation Exponential notation is a way of displaying a number as a digital number multiplied by a power of 10 In the number 5e3 for example 5 is the digital number and 3 is the power to which 10 is taken Interpret 5e3 as 5 times the quantity 10 taken to the power of 3 which equals 5 000 in decimal notation A burning and expanding gas cloud formed during a BLEVE of a flammable chemical The fireball is made up of both the chemical that flash boils when the tank fails and the chemical that sprays out as an aerosol during the explosion The primary hazard associated with a fireball is thermal radiation Easy to ignite and burns readily The U S Department of Transportation defines flammable liquids as those liquids that have a flash point below 100 F 37 8 C 174 Glossary Flammable area Flash fire Flash point Flash boil Footprint Freezing point The part of a flammable vapor cloud where the concentration is in the flammable range between the Lower and Upper Explosive Limits LEL and UEL The flammable area will burn rapidly when ignited because that portion of the cloud is already pre mixed to the right mixture of fuel and air for burning to occur Following the rapid burning the part of the cloud where the fuel air concentration is above the UEL may continue to slowly burn as air mixes with the cloud When a flammable vapor cloud encounte
165. laminar burning velocities Dense smoke like vapors given off by fuming materials such as very reactive liquids gases or molten metals for example concentrated hydrochloric acid or sulfur monochloride Fuming corrosive materials produce dense choking smoke like clouds on contact with the moisture in air Some liquefied gases that react with water when they evaporate such as anhydrous hydrogen fluoride and anhydrous hydrogen chloride also produce fumes Fumes from hot or molten metals may not have a dense smoke like appearance but are hazardous usually by inhalation Evenly dispersed molecules of a material at a temperature above its boiling point A gas unlike solids and liquids does not have an independent shape or volume a gas expands to fill available space and the volume taken up by a gas depends on the pressure exerted on it Examples of gases include oxygen air a mixture of nitrogen oxygen and trace amounts of other gases chlorine and carbon dioxide A Gaussian curve is a bell shaped or normal probability curve named after a famous mathematician ALOHA uses a Gaussian distribution to describe the movement and spreading of a gas that is neutrally buoyant about as dense as air Greenwich Mean Time or Coordinated Universal Time The reference time along the prime meridian 0 longitude which passes through Greenwich England 176 Glossary Ground roughness Ground temperature Ground type
166. lass in which case they usually pick stability class F to model the worst case scenarios Inversion height An inversion is an atmospheric condition in which an unstable layer of air near the ground lies beneath a very stable layer of air above The height of the abrupt change of atmospheric stability is called the inversion height An inversion can trap pollutant gases below the inversion height causing ground level concentrations of a pollutant to reach higher levels than would otherwise be expected 120 Chapter 4 Reference The type of inversion of concern for dispersion modeling is a low level inversion that could trap a pollutant cloud near the ground Sea smoke and low ground fog are good indicators of the presence of this type of inversion A low level inversion is different from the inversion that causes smog That type of inversion is typically thousands of feet above the ground much too high to affect a dispersing gas cloud ALOHA s Gaussian dispersion model accounts for inversions but the heavy gas Atmospheric Options 2 model does not even when you ve indicated Temperature is 172 cic so A a Help that an inversion exists A low level Stability Classis Help C a BOC COC CF Override inversion may significantly increase ground inversion Height Options are Help level concentrations of a neutrally buoyant No Inversion Inversion Present Heightis lt pies gas Molecules of such gases disperse
167. lease e When you enter information into ALOHA you often have to guess at some of the necessary inputs e Many things that happen by chance such as unexpected changes in wind speed or direction during a release can influence how a gas cloud disperses but are not accounted for in ALOHA s computations e Although ALOHA is a relatively complex computer program it contains thousands of lines of computer code reality is much more complex ALOHA makes simplifying assumptions in order to make its predictions Try to identify ways in which reality may be different from what ALOHA assumes For example ALOHA expects the terrain under a dispersing gas cloud to be flat and free of obstacles but in the real world that s rarely the case Treat any threat zone plot as a ballpark estimate and always use it along with never instead of your own judgment experience and observations when you make response or planning decisions Displaying threat zones in other applications Threat zones can also be overlaid on electronic maps displayed in ALOHA s companion mapping application MARPLOT You can also import an ALOHA threat zone plot into either of two Geographic Information System GIS products manufactured by ESRI ArcView and ArcMap To import a threat zone plot you will need to download and install the appropriate plugin from NOAA s Office of Response and Restoration Web site http response restoration noaa gov cameotoolkit Threat at Po
168. line source 146 147 Puddle source 132 136 release rate 130 sources and scenarios table 128 Tank source 136 145 source height 132 source strength about 156 averaging 158 constant 157 variable 157 stability class about 119 overriding ALOHA 120 wind speed table 120 Stack Windows menu item 158 street canyon 29 184 sublimation rate 134 T Tank source 136 145 BLEVE 141 chemical state 138 contains gas 140 contains liquid 139 describing the leak 143 fireball 142 ground temperature 145 ground type 144 height of leak 144 leaking tank 141 liquefied gases 137 193 Index orientation of 138 puddle area 145 puddles 137 144 size of 138 storage temperature 139 type of tank failure 141 TEELs 184 terrain effect on puddles 31 terrain steering 29 184 Text Summary about 156 chemical data 109 Gas Pipeline source 147 notes 110 thermal radiation burn injury table 20 definition of 184 Levels of Concern 20 transmissivity 121 Threat at Point about 153 fixed coordinates 154 MARPLOT 161 relative coordinates 154 results 154 threat distance definition of 185 example of 60 threat zone colors 152 displaying in other applications 153 flammable vapor clouds 149 interpreting 153 Level of Concern 150 MARPLOT 161 menu item 149 plot 152 threat zone plot 152 Tile Windows menu item 158 timestep 130 toxic byproducts from fire 19 two phase flow definition of
169. ll take a very long time to mix completely into the coffee without stirring it Similarly the cloud will spread slowly and high gas concentrations may build up in small valleys or depressions and remain for long periods of time even at distances far from the release point ALOHA does not account for buildup of high gas concentrations in low lying areas 28 Chapter 1 Welcome to ALOHA First responders should be aware that very stable atmospheric conditions create a dangerous situation in which models like ALOHA are not very reliable In this situation think about whether the chemical will behave as a heavy gas and look for physical depressions and topographic features that may trap or steer the dispersing cloud Wind shifts and terrain steering effects ALOHA allows you to enter only single values for wind speed and wind direction It then assumes that wind speed and direction remain constant at any given height throughout the area downwind of a chemical release ALOHA also expects the ground to be flat and free of obstacles In reality though the wind typically shifts speed and direction as it flows up or down slopes between hills or down into valleys turning where terrain features turn The way in which land features modify patterns of air flow is called terrain steering and it is shown in Figure 1 3 Figure 1 3 Wind shifts from terrain steering In urban areas wind flowing around large buildings forms eddies and chan
170. llons Select an instantaneous or continuous source C Instantaneous source Continuous source Enter the amount of pollutant ENTERING THE ATMOSPHERE Help pounds sec 100 C pounds min for 60 minutes C poundsfhr 1 60 Enter source height feet 0 if ground source 0 c meters 131 Chapter 4 Reference Type either the amount of pollutant entering the atmosphere for an instantaneous release or the rate of entry for a continuous release For a continuous source this value must be expressed as a rate such as pounds per minute This is the rate at which a chemical is being released into the atmosphere i e the rate at which a gas is escaping from a tank or the evaporation rate of a puddle If you must estimate or guess the amount or rate try entering the largest likely amount or rate as well the smallest likely amount or rate into ALOHA then check to see how the size of the threat zone changes when your amount estimate changes Source height The source height is the height of the location of a chemical release above the ground Source height is zero if the chemical is released at ground level Enter a source height greater than zero to model a release from an elevated source only if ALOHA is making Gaussian dispersion calculations ALOHA does not account for any substantial upward or downward movement of a gas cloud in the atmosphere Enter a non zero source height only when the released chemical dispers
171. losion This pressure wave is caused by the energy released in the initial explosion the bigger the initial explosion the more damaging the pressure wave At equilibrium molecules move from the liquid to the gas phase at the same rate as they return to the liquid from the gas phase In liquids that are mixtures of chemicals each component vaporizes evaporates at its own characteristic rate The partial pressure of a chemical in a mixture is a measure of the concentration of that chemical s gas phase molecules in the air directly in contact with the liquid In most actual cases equilibrium is not reached so the partial pressure represents the limiting value for chemical concentration in the air 180 Glossary Particulates Parts per billion ppb Parts per million ppm Plume Plume rise Pool fire Relative humidity Release duration Solid particles so small that they can disperse in the air like gases however unlike gases particulates eventually rainout or fall to the ground ALOHA does not model particulate dispersion Units of gas or vapor concentration in air parts of gas per billion parts of air ALOHA uses parts per million ppm 1 ppm 1 ppb x 1 000 Units of gas or vapor concentration in air parts of gas per million parts of air In ALOHA ppm is by volume not by weight A cloud of pollutant gas dispersing from a continuous source A typical plume is a long cigar shaped gas cloud Th
172. ly overcast Under Select Cloud Cover choose the complete cover options Notice that ALOHA has filled in a value of 10 Click OK The second Atmospheric Options dialog box appears Atmospheric Options Wind Speedis 10 C knots mph meters sec Help Wind is from jeo Enter degrees true or text e g ESE Measurement Height above ground is Help C c a g h OR entervalue 10 feet meters Ground Roughness is Help C Open Country c Urban or Forest OR Input Roughness Zo C Open Water Select Cloud Cover Help a re a go OR entervalue 10 i Cc C c 0 10 partly cloudy complete clear cover eo Cancel 68 Chapter 3 Examples 6 The air temperature is 70 F Type 70 in the air temperature box then Atmospheric Options 2 Air Temperature is 70 Degrees CF CC Help select F g Stability Classis Help C 4 CBE CDC F Override 7 ALOHA uses the wind speed cloud Hee Denice cover and date and time Inversion Height Options are Help No Inversi Inversion Pi t Hei co Ee information that you ve entered to ash Albstio version tresent Heightis C meters automatically select atmospheric Select Humidity Help Stability Class D representing ka a conditions of neutral atmospheric s Pie re rE X 67 stability medium dry 0 100 Cancel 8 There is no low level inversion Check to be sure that No Inversion is selected 9 The relative humidity is 6
173. m the Sharing menu CAMEO menu When CAMEO is running a CAMEO menu appears in ALOHA s Sharing menu The CAMEO menu in ALOHA s Sharing menu contains two items e If you have selected a chemical in ALOHA choose Get RIDS Info to see information about this chemical in CAMEO s RIDS Response Information Data Sheets database e Choose Go to CAMEO to start CAMEO or to go to CAMEO if it is already running About Shared Menus Edit Shared Menus CAMEOFm gt Get RIDS Info MARPLOT b Go to CAMEOFm 159 Chapter 4 Reference MARPLOT menu The MARPLOT menu in ALOHA s Sharing menu contains two items e Choose Help to learn about information sharing between MARPLOT CAMEO s mapping program and ALOHA e Choose Go to Map to start MARPLOT or to go to MARPLOT if it is already running About Shared Menus Edit Shared Menus CAMEOFm gt MARPLOT gt Help Go to Map Use MARPLOT with ALOHA to display an ALOHA threat zone plot on an electronic map of your community MARPLOT can display several different types of maps It was primarily designed to use special maps generated from TIGER Topologically Integrated Geographic Encoding and Referencing files prepared by the U S Census Bureau from U S Geological Survey base maps TIGER files are computer readable geographic databases for all U S states territories and possessions They include digital descriptions of features such as political boundaries water bodies t
174. me represents the length of time that the cloud mixes with the air around it and becomes diluted in concentration Therefore the amount of the vapor cloud that is between the Lower and Upper Explosive Limits LEL and UEL will depend on the ignition time Enter the time in minutes or seconds If you do not know the ignition time ALOHA allows you to choose an unknown ignition time option 150 Chapter 4 Reference If you choose the unknown ignition time option ALOHA will run explosion scenarios for a range of ignition times that encompass all of the possible ignition times for your scenario ALOHA takes the results from all of these scenarios and combines them on a single threat zone plot The threat zone in this case does not represent the blast area from a single explosion but rather the composite of potential blast areas for all of the different ignition time scenarios that ALOHA ran Note If you are modeling an instantaneous release from a Direct source ALOHA models the chemical release for 60 seconds If you choose an ignition time less than 60 seconds not all of the chemical will be released prior to the explosion Vapor Cloud Explosion Parameters Time of vapor cloud ignition Help C unknown show composite threat zone from all possible ignition times known ignition time is minutes 3 after the beginning of the release C seconds Type of vapor cloud ignition Help ignited by spark or flame C ignited by deton
175. midity and uses the transmissivity when estimating thermal radiation threat zones Lower relative humidly values will result in longer threat zone estimates Response techniques like a water fog artificially increase water vapor and decrease the transmissivity in the incident area to try to reduce the thermal radiation hazard Enter a relative humidity value in either of two ways either select the option that best represents your relative humidity value or type the relative humidity as a percentage in the humidity value box 121 Chapter 4 Reference SAM Station Although you can enter all weather information into ALOHA manually ALOHA can also accept data from an external portable meteorological monitoring station called a Station for Atmospheric Measurement SAM SAM data can be transmitted to ALOHA by either radio frequency or a cable ALOHA can use SAM measurements of wind speed and direction standard deviation of the wind direction and air temperature ALOHA cannot accept relative humidity readings made by a SAM you ll need to enter these measurements into ALOHA manually Choosing a SAM A few companies manufacture SAMs for use with ALOHA Before purchasing a SAM to use with ALOHA check with its manufacturer to be sure that it is designed to work with ALOHA and to learn how to connect the station to your computer so that it can transmit data to ALOHA Before using a station not specifically designed for ALOHA be sure th
176. mmary of the information that you entered and the source strength results calculated by ALOHA If at least some liquid is present in the tank you will need to enter some more information on the Height of the Tank Opening dialog box before ALOHA can estimate source strength If the chemical is stored as a liquefied gas a liquid at a temperature above its boiling point ALOHA may expect it to escape from the tank under pressure as a two phase mixture of gas and liquid In liquefied gas cases your choice of opening type can have an important effect on ALOHA s release rate computations ALOHA will predict a higher release rate for a two phase release if you choose the hole option rather than the short pipe valve option Opening type does not make a difference in a pure gas or unpressurized liquid release case 143 Chapter 4 Reference Height of the Tank Opening If there is liquid in the tank you must tell ALOHA where the leak occurs on the tank Enter a value for the height of the bottom of the leak whether it is a hole short pipe or valve above the floor of the tank ALOHA uses this value to determine whether the leak is above or below the liquid level If an unpressurized liquid is stored in the tank and the leak is below the liquid level the chemical will spill out and form a puddle on the ground It will stop spilling once the liquid level falls below the bottom of the leak If the leak is above the liquid level and an unpressurize
177. n liquefied by applying a high pressure or by cooling refrigerating it below its boiling point Chemicals that are stored as liquefied gases are gases at ambient pressure and or temperature The Lower Explosive Limit LEL also called the Lower Flammability Limit is the minimum concentration of fuel in the air needed for a fire or an explosion to occur if an ignition source is present If the concentration is below the LEL there is not enough fuel in the air to sustain a fire or an explosion it is too lean The LEL is determined experimentally using standard temperature and pressure settings Additionally if the fuel concentration in the air exceeds the Upper Explosive Limit UEL then a fire or an explosion cannot occur Mass is a physical property related to weight Mass is a measure of the amount of a substance that occupies a given space While the weight of a given amount of a substance is a measure of the force by which it is attracted by gravity and is less on the moon than on the earth the substance s mass is independent of gravity ALOHA computes release rate from a puddle tank or gas pipeline as a series of hundreds of brief timesteps Each timestep represents a rate of release that is maintained for a particular amount of time timesteps are short if release rate is changing rapidly and longer if release rate is nearly constant For releases into the atmosphere ALOHA averages this series of many release rates into
178. n model three different hazards toxic area flammable area and blast area If you are modeling a flammable vapor cloud or a situation where such a cloud might form a Hazard To Analyze dialog box will appear after you choose Threat Zone from the Display menu In this dialog box you must first select the hazard that you want ALOHA to model before you can choose your LOCs Additionally if you select blast area from a vapor cloud explosion you will have to complete the Vapor Cloud Explosion Parameters dialog box before you can choose your LOCs 149 Chapter 4 Reference Level of Concern A Level of Concern LOC is a threshold value of a hazard toxicity flammability thermal radiation or overpressure the LOC is usually the value above which a threat to people or property may exist You may keep ALOHA s default values as your LOCs or you may choose up to three of your own LOCs For each LOC you choose ALOHA estimates a threat zone where the hazard is predicted to exceed that LOC at some time after a release begins You may designate LOC values in one of three ways e Use ALOHA s default LOC choice e Use the LOC pulldown menus to choose another LOC from the list e Select User specified from the LOC pulldown menu and enter your own temporary LOC value and select the appropriate units Note You can add your own default Toxic LOC for any pure chemical in ALOHA s chemical library ALOHA will then use your LOC by default rather than
179. nds min averaged over a minute or more Total Amount Released 3 682 pounds Note The chemical escaped as a liquid and formed an evaporating puddle The puddle spread to a diameter of 21 7 yards THREAT ZONE Model Run Heavy Gas Red 82 yards 1666 ppm ERPG 3 Orange 281 yards 156 ppm ERPG 2 Yellow 564 yards 56 ppm ERPG 1 60 Chapter 3 Examples Modeling a second scenario pool fire Now that ALOHA has displayed the downwind distance to the ERPG 2 level you want to assess the thermal radiation threat if the puddle is ignited by a lightning strike or other ignition source and forms a pool fire For this example you want to assess the threat assuming that the pool fire occurs soon after the puddle forms Therefore you do not need to enter new information for time atmospheric conditions or puddle size 1 When you run multiple scenarios for the same incident the plots and Text Summary screen from the first scenario will change when you enter new information Before you start running an additional scenario either print out the threat zone plot and the Text Summary screen or paste them into a word processing document You ll need the original information to compare the scenarios later Close the threat zone plot window When you set the source for the first scenario you told ALOHA that the benzene was leaking from a tank but it was not burning You need to return to the Type of Tank Failure scr
180. ne plots for a flammable vapor cloud 76 Modeling a third scenario jet Tre os ayescissucsaius iectuseaseunt ales secede j es adadenc toads easemeedaved 82 Choosing LOCs and creating a threat zone plot for a jet fire 0 0 0 eeeeeeteeeeeeee 83 Example 3 A Direct Source and a MARPLOT Map uu eee eeeeeseceseeeeeeeeaeecnaeeneeeaeees 85 Choosing a location and a Chemical 0 eesceeescceceseeceeeeeceeeeecseeeeeseeeeneeeeneeeeaees 85 Entering weather information sisecc scicsececcecvececnsvedesentdeedeie da eecaceeth Gesuteasecnsacedeeeur tees 87 Describing the releases rero iieii Pe aoa ae BAe ee 88 Choosing LOCs and creating a threat zone plot 0 0 eee eeececeeeeeceeeeeceteeeesteeeeeaes 90 Using MARPLO T hersiene tre arna EEA AER E O E TAEAE E ERES 92 Chapter 4 Reference ois s 55 4 stein s 5 usea en i E BSS 99 File men sssrinin isi ieee E ESE STEE A NE ESARETTE ia 99 NeW nee e e o Rated E a A lead E S 99 Opeta ee t r a ea tant cats S ae a yaa aaa Shag at NS 99 Response Modes ss sssccistiassiccs ceased cieddacs a A R Ei 99 Planing Modenan agate onde unde E A Baie dias 99 Close eiers ei ea E E E hal E gina acest yy otek EEES nats 100 Save and Save ASviastadinwe tiie asii a anars TE a aT aa 100 Print Print All and Print or Page Setup iasgac teint canoe er oh asi actetenian 100 Q it or AE aS vals Sas iosi a iad a i a aa iiaia s aa 100 Edit MENU nonsi nasii issii ahaa ie iit ae 100 COPY niese n a Gels eet Oakes E als ea tea ase
181. ng point of the liquid that they contain It cannot estimate sublimation rate for a frozen puddle a frozen substance sublimes when it passes directly to the gas state without first becoming liquid 134 Chapter 4 Reference Area and Volume Enter the puddle area or if the puddle is roughly circular type its approximate diameter and ALOHA will estimate its area If the puddle is roughly square or rectangular in shape you must enter its area equal to its length multiplied by its width If the length and width are in units of feet then the area will be in units of square feet if the diameter or the length and width are in meters the area will be in square meters and so on Puddle area strongly influences the evaporation rate or burn rate if the puddle is burning When all else is equal the larger the area of a puddle the higher is its evaporation rate or burn rate Next enter the amount of chemical contained in the A Puddle Input puddle Specify the amount of liquid contained in the feet o d puddle by selecting Puddle O Sieneter S 25 square C a e Volume of puddle Select one and enter appropriate data Volume of puddle e Average depth of puddle or C Average depth of puddle e Mass of puddle Mass of puddle 7 gallons C liters Volume is 300 C cubicfeet cubic meters Type a volume depth or mass value in the corresponding box and select the appropriate units Cancel Help Gr
182. ng and the population that you re concerned about Treat ALOHA s threat zone as a rough estimate of the true hazard zone for a chemical release 1 Choose Threat Zone from the Display menu A Toxic Level of Concern dialog box appears Threat Zone Ctrl F y Text Summary Ctrl K Source Strength cCtril G Tile Windows Stack Windows Display Options Ctrl 43 Chapter 2 Learning the Basics 2 Decide which LOC values you want ALOHA to use to define the threat zones For this example you ll keep the default LOCs for chlorine the Acute Exposure Guideline Levels AEGLs Note the AEGL level increases with increasing hazard Therefore ALOHA uses AEGL 3 for the red threat zone Many other toxic thresholds besides AEGLs exist Click the Help button on the Toxic Level of Concern dialog box to learn more about choosing an LOC What do the AEGL levels represent AEGL 1 The airborne concentration of a substance above which it is predicted that the general population including susceptible individuals could experience notable discomfort irritation or certain asymptomatic nonsensory effects However the effects are not disabling and are transient and reversible upon cessation of exposure AEGL 2 The airborne concentration of a substance above which it is predicted that the general population including susceptible individuals could experience irreversible or other serious long lasting adverse health effects or an impaire
183. nk Size and Orientation dialog box appears Notice that all of your original information is already entered into the dialog box The dimensions of the tank have not changed so you can just click OK to move to the next screen Your original information is still correct on the Chemical State and Temperature and the Liquid Mass or Volume dialog boxes Click OK on each screen until the Type of Tank Failure dialog box appears Choose the Leaking tank chemical is not burning as it escapes into the atmosphere option Click OK An Area and Type of Leak dialog box appears Type of Tank Failure Scenario Tank containing a pressurized flammable liquid Type of Tank Failure Leaking tank chemical is not burning as it escapes into the atmosphere C Leaking tank chemical is burning as a jet fire C BLEVE tank explodes and chemical burns in a fireball Potential hazards from flammable chemical which is not burning as it leaks from tank Downwind toxic effects Vapor cloud flash fire Overpressure blast force from vapor cloud explosion Cancel 74 Chapter 3 Examples The tank appears to be intact However you want to model a release assuming a seam fails on the tank creating a rectangular hole 40 inches long and 0 1 inch wide Select Rectangular opening Type 40 in the opening length box and select inches Type 0 1 in the opening width box Choose the Hole option Click OK A Height of the Tank Opening dialog bo
184. nk explodes and chemical burns in a fireball Choose the Leaking tank chemical is burning asa jet fire Potential hazards from chemical which is burning as it leaks from tank option Click OK An Area and Thermal radiation from jet fire Type of Leak dialog box appears BLEVE E 3 if heat causes the tank to fail Your original information is still Downwind toxic effects of fire byproducts correct on the Area and Type of cannot be modeled by ALOHA Leak dialog box Click OK A Height of the Tank Opening dialog box appears Cancel ALOHA models jet fires assuming the opening is on the top of the tank Type 100 in the of the way to the top of the tank box Click OK Text Summary that you have entered and the SOURCE STRENGTH Leak from hole in horizontal cylindrical tank results of ALOHA s source strength Flammable chemical is burning a it escapes from tank calculations appear in the Text Tank Diameter 9 67 feet Tank Length 76 feet Tank Volume 33866 gallons mm imi 1 Tank contains liquid Internal Temperature 76 F Su ary ALOHA limited the jet Chemical Mass in Tank 70 1 tons Tank is 100 full fire to one hour and estimated that Opening Length 46 inches Opening Width 6 1 inches Opening is 9 67 feet from tank bottom the Maximum Burn Rate is 5 730 Max Flame Length 36 yards Burn Duration ALOHA limited the duration to 1 hour pounds per minute Max Burn Rate 5 736 pounds min Total Amount Burne
185. ns the file it will restore the information contained in the file that is expected to stay the same from day to day This information includes location chemical of concern and the dimensions of existing storage vessels and containment areas You ll need to enter information specific to your incident including current weather conditions and the circumstances of the release these could include for example the dimensions and location of a hole in a tank or the area of a puddle of spilled liquid Planning Mode Choose this mode when you want to look at a saved scenario again with all of the same input values as at the time it was saved If you were using the computer s clock to set the time ALOHA will use the time when the file was saved as the constant time If you were using a portable weather monitoring station SAM the most recent transmission will be entered into ALOHA as user entered atmospheric data Saved files created from the current version of ALOHA are cross platform you can open a save file created in Microsoft Windows on a Macintosh computer and vice versa 99 Chapter 4 Reference Close Choose Close to close ALOHA s front window However you cannot close the Text Summary window Save and Save As Choose Save or Save As when you want to save the results of your work in a data file Do this if you wish a to prepare in advance for an incident response by creating a set of saved ALOHA files or b to be able
186. o their contact information This information is necessary so that the United States Government may notify users of any ALOHA program changes or if updated information becomes available Trademarks CAMEO ALOHA and MARPLOT are registered trademarks of the United States Government Table of Contents Chapter 1 Welcome to ALOHA cece cece eer cree ee eecnes 11 About ALOHA 95 kis scons tesceussncesitealtesdvtnes iam ataacnordocunlaredybsdelye Macaw cossstyalbseviaecaueeMaats 11 Programi PULPOSE nesune nin ne esia a ne cdasesansdaadassaned EN Seas 11 Basic prosrani rsanizati oM isoa niea a a a alah Mae een 11 ALOHA S menu bari nnan hen rea Goer tigate aa a n n as 13 Getting Nel ps ccctictisccsdunc cade n a E E A a a A aaen 14 Ti Windows deta tse e ea a AS 14 O a Macint s hansr ste se teva inesset cbs aie ade ea S oar cacel iatacte ees 14 How t use this manual 22 04 csc2ician siirsin Milde bed Nee kee 14 Modelinein ALOHA sects coh etalon erento ae E ena E ete nataless 15 Introduction to dispersion WMOde IU gi 2cce3e Falcone ices Geeta dash cases dade cpenezsdales tonto eae daeenees 15 What 1s Uisperston mpenn ii n seeeadavagd E aE A D EE Ei 16 Ga ssian model korei it n ne oe EA dale R E EE EESE 16 Heavy gases etzara a nee sea 17 Classification of heavy gases seseeseseesesesesressessresressersrerressessesseerressesee 17 Flash boiling and two phase floW ese eeseceseceseeeseeceseeeseeeeneecaeeeseenses
187. occurring select Location from the SiteData menu You ll see a scrolling alphabetical list of cities mostly U S cities and towns Scroll through the list to speed your search type the first one or two letters of the city name click on the city name then click Select Location Information SHERMAN TEXAS a Select ie SMITHTOWN NEW YORK SNOHOMISH WASHINGTON Cancel SOMERSWORTH NEW HAMPSHIRE SOMERVILLE MASSACHUSETTS nF SOUTH BEND INDIANA SPARKS NEVADA SPARTANBURG SOUTH CAROLINA Modify SPOKANE WASHINGTON ee SPRINGFIELD ILLINOIS ST ALBANS WEST VIRGINIA Delete ST CHARLES MISSOURI G ST JOSEPH MISSOURI ST LOUIS MISSOURI bg Help 101 Chapter 4 Reference Adding modifying and deleting location information You can add a new city or other geographic location to ALOHA s library of cities CityLib You can add both U S and non U S locations to the library For a location outside of the U S you must manually change the time setting whenever time at the location switches between daylight savings and standard time Be as accurate as you can when entering information about a location ALOHA uses your values for elevation latitude and longitude to calculate solar radiation and air pressure However small errors in location information don t affect the accuracy of ALOHA s predictions An estimate is accurate enough if it is within a degree or so in latitude and longitude and a few hundre
188. odel ALOHA uses the Gaussian model to predict how gases that are about as buoyant as air will disperse in the atmosphere Such neutrally buoyant gases have about the same density as air According to this model wind and atmospheric turbulence are the forces that move the molecules of a released gas through the air so as an escaped cloud is blown downwind turbulent mixing causes it to spread out in the crosswind and upward directions According to the Gaussian model a graph of gas concentration within any crosswind slice of a moving pollutant cloud looks like a bell shaped curve high in the center where concentration is highest and lower on the sides where concentration is lower as in Figure 1 1 At the point of a release the pollutant gas concentration is very high and the gas has not diffused very far in the crosswind and upward directions so a graph of concentration in a crosswind slice of the cloud close to the source looks like a spike As the pollutant cloud drifts farther downwind it spreads out and the bell shape becomes wider and flatter 100 80 60 40 Concentration ppm Concentration Crosswind Distance Source of Spill Crosswind Figure 1 1 Gaussian distribution left and Gaussian spread right 16 Chapter 1 Welcome to ALOHA Heavy gases When a gas that is heavier than air is released it initially behaves very differently from a neutrally buoyant gas The heavy gas will first slump or sink
189. of all preceding characters in the data line including the carriage return and line feed characters and the preceding comma 122 Chapter 4 Reference During the first five minutes of data collection the SAM should transmit as its value for SD sigma theta Although a station ID number must be included in each data transmission ALOHA does not use this value Wind direction should be the direction from which the wind is blowing If the SAM checks automatically for invalid data and finds an erroneous value it should transmit a data line that includes in place of that value either no value the data line would then contain two successive commas with no value between them or a word such as error as its value for an invalid datum the data line would then contain error Because ALOHA does not check SAM data transmissions for unacceptable values the SAM should not transmit a numeric value such as 999 in place of an erroneous value Using a SAM during an incident When you use a SAM with ALOHA during incident response place your SAM so that its readings will be as representative as possible of the whole area through which the pollutant cloud may travel Be sure to place it at a location such as an open field parking lot or clearing where the wind is not affected by obstacles such as trees buildings or hills Avoid placing a SAM in the lee of buildings vehicles or other obstacles to wind flow where wind sp
190. oice If your value for initial puddle temperature is above the liquid s normal boiling point ALOHA will alert you and allow you to set the initial puddle temperature to the boiling point If the puddle is burning you only need to enter the initial puddle temperature because ground type and ground temperature do not affect pool fire Initial Puddle Temperature Input initial puddle temperature Help calculations ALOHA assumes the initial Use air temperature select this if unknown temperature to be the same throughout the depth 9 Mi Rate te mp arta B55 and width of the puddle Cancel Tank In the SetUp menu point to Source then select Tank Choose the Tank source option to model releases of unpressurized liquids liquefied gases or pressurized gases from tanks or drums ALOHA can model leaks that release the chemical directly into the atmosphere as well as leaks that form an evaporating puddle If the chemical is flammable ALOHA can also model BLEVEs pool fires and jet fires Chemical Ctrl H Atmospheric gt Puddle Ctrl U Calculation Options Gas Pipeline Ctrl I N 136 Chapter 4 Reference You can choose to model releases from three types of tanks a cylindrical tank lying on its side a cylindrical tank standing on its end or a spherical tank ALOHA assumes any tank to be on level ground If the tank contains pressurized gas or liquid ALOHA computes the change over time in pressure and tempe
191. ompensate for this effect Some experiments have shown that flame pockets can occur in places where the average concentration is above 60 of the LEL ALOHA uses 60 of the LEL as the default LOC for the red threat zone Another common threat level used by responders is 10 of the LEL ALOHA uses this concentration as the default LOC for the yellow threat zone Vapor cloud explosions When a flammable chemical is released into the atmosphere it forms a vapor cloud that will disperse as it travels downwind If the cloud encounters an ignition source the parts of the cloud where the concentration is within the flammable range between the LEL and UEL will burn The speed at which the flame front moves through the cloud determines whether it is a deflagration or a detonation see next page In some situations the cloud will burn so fast that it creates an explosive force blast wave The severity of a vapor cloud explosion depends on the chemical the cloud size at the time of ignition the type of ignition and the congestion level inside the cloud The primary hazards are overpressure and hazardous fragments ALOHA can help you model the overpressure hazard 26 Chapter 1 Welcome to ALOHA Deflagration and detonation The destructive blast force of a vapor cloud explosion depends in part on how quickly the explosion spreads that is the rate at which its flame front travels Once an explosion has been triggered a flame front will spread
192. omputer s serial port A file containing information about a release scenario that you have entered into ALOHA You can reopen and modify a save file in ALOHA Choose Save from the File menu to create a save file A data interface on a computer through which peripheral devices such as a SAM scanner printer or digitizing tablet can be connected ALOHA can receive weather data from a SAM through a serial port The standard deviation of the wind direction A SAM configured for use with ALOHA measures changes in wind direction then transmits an estimate of sigma theta ALOHA uses this value for sigma theta and the wind speed to estimate stability class A mixture of gases suspended solid particles and vapors resulting from combustion A measure of a chemical s ability to dissolve in water If a chemical is highly soluble it will dissolve easily into water 182 Glossary Solution strength Solutions Source Source height Source Strength Stability class Stable Mixtures of chemicals in which the components are interspersed uniformly at the molecular level are called solutions The strength of a solution in ALOHA is defined as the mass of the volatile hazardous component divided by the mass of the solution For example the strength of an oleum solution is defined as the mass of free sulfur trioxide divided by the combined mass of the free sulfur trioxide and sulfuric acid Mixtures of chemicals in which the
193. on but feel that you can make a ballpark estimate of the total amount of chemical released into the atmosphere Note In ALOHA direct refers to the fact that the scenario information is directly entered by the user bypassing ALOHA s source calculations Whenever you must estimate a value try entering the largest likely value as well the smallest likely value into ALOHA then check to see how the size of the threat zone changes when your value changes If you have enough information about the release you may wish to choose the Puddle Tank or Gas Pipeline source option instead so that ALOHA will make the estimates for you Chemical Ctrl H Atmospheric gt EY Puddle Ctrl U Calculation Options Tank Ctrl4T Gas Pipeline Ctrl I 130 Chapter 4 Reference To model a direct release of gas into the atmosphere you will need to estimate the amount of pollutant directly entering the atmosphere as a gas This could be the amount of pollutant vapor evaporating from a puddle or the amount of gas escaping from a gas pipeline or tank rupture It would not be the amount of liquid spilling from a tank and forming a puddle because the liquid is not directly entering the atmosphere In this case you need to estimate the rate at which the gas enters the atmosphere i e evaporation rate rather than the spill rate Accurately estimating the rate of release When modeling a Direct source you can only enter a constant rate for
194. oordinates Evaluation Downwind Crosswind Point n Wind direction C Fixed Coordinates v EastWest North South gt p x Input X the downwind Source distance from the source and Y the perpendicular distance from the downwind axis feet Input X the downwind distance 1500 yards miles Input Y the crosswind distance 0 meters kilometers Cancel Help 46 Chapter 2 Learning the Basics ALOHA then displays a graph of predicted chlorine concentrations at the school during the hour after the release begins The horizontal axis of this graph represents time from 0 to 60 minutes after the release starts and the vertical axis represents concentration at the location expressed in parts per million ppm The solid thin red line represents the predicted outdoor ground level concentration The dashed blue line represents predicted concentration inside a building of the type you selected using the Building Type menu item in the SiteData menu To draw this line ALOHA assumes that the building s doors and windows are closed and that its ventilation system is off The horizontal red orange and yellow lines represent the LOCs in this case AEGL 3 AEGL 2 and AEGL 1 respectively F Concentration at Point BEGL 3 60 min AEGL 2 60 min AEGL 1 60 min minutes Outdoor Concentration Indoor Concentration t Point Downwind 1500 yards Off Centerline 0 yards ALOHA predicts that the cloud of
195. oose Chemical from the SetUp menu then click Modify When you choose Use Heavy Gas dispersion only ALOHA will predict the dispersion of the pollutant using the heavy gas computations Typically when the atmosphere is most unstable stability classes A and B heavy gas threat zones will be longer than Gaussian threat zones When the atmosphere is most stable stability classes E and F Gaussian threat zones will be longer Under neutral C and D conditions heavy gas and Gaussian threat zones will be similar in length Display menu Select items from the Display menu to indicate the ALOHA results that you would like to see and how you would like the information to be Threat Zone Ctrl F displayed Threat At Point Ctri R e Choose Threat Zone Threat at Point Text Summary and or Text Summar Ctrl K Source Strength to display the corresponding windows J Source Strength cCtril G e Choose Tile or Stack to organize ALOHA s windows on your screen Tile Windows Stack Windows e Choose Display Options to have ALOHA s output displayed in Display Options Ctrl either English or metric units tie a aia Threat Zone Choose Threat Zone from the Display menu to have ALOHA create a threat zone plot where up to three hazard levels are plotted based on your Levels of Concern LOC Once you select Threat Zone from the Display menu you must specify one or more LOCs Note For flammable vapor clouds ALOHA ca
196. orange and yellow overlaid on a single plot By default the red zone represents the worst hazard The pattern of dots also varies for each threat zone so that you can differentiate between the zones if you are color blind or the plot has been printed in black and white E Toxic Threat Zone 0 500 1000 yards gt 20 ppm AEGL 3 60 min gt 2 ppm AEGL 2 60 min m gt 0 5 ppm AEGL 1 60 min Confidence Lines On ALOHA s threat zone plot for all dispersion scenarios the dashed lines along both sides of the threat zone represent uncertainty in the wind direction The wind rarely blows constantly from any one direction As it shifts direction it blows the released chemical in a new direction The uncertainty lines around the threat zone enclose the region within which about 19 out of 20 times the chemical cloud is expected to remain The lower the wind speed the more the wind changes direction so as wind speed decreases the uncertainty lines become farther apart They form a circle when wind speed is very low 152 Chapter 4 Reference Interpreting a threat zone ALOHA s threat zone estimate represents its best guess of what will happen downwind of a chemical release It s not an exact prediction of just where the gas cloud will travel and how large it will be As you examine any threat zone plot remember the many uncertainties involved in trying to predict the effects of a chemical re
197. orine for only a few minutes However if the wind shifted during the course of the release the concentration at the workmen s location could have been higher or lower than ALOHA s estimate If you were to respond to a real event similar to this example you might wish to obtain values for the tank s dimensions the size and location of the hole and other information that you d need to run ALOHA s Tank source option which takes time dependent release rates into account 12 When you ve finished this example problem simply choose Exit in Windows or Quit on a Macintosh from MARPLOT s File menu ALOHA s threat zones will then be deleted from the map 98 Reference Refer to this chapter for detailed explanations of ALOHA program operations features and menu items The sections of this chapter correspond to ALOHA s menus File menu New New Ctrl N Choose New to clear all information about a scenario from oldie ALOHA before beginning a new scenario When you choose this Close Ctrl menu item you have the option of saving your old scenario Save Ctrl S before clearing ALOHA Save As Print Ctrl P Open Print All Print Setup Choose Open to open a previously saved ALOHA file Whenever you open a saved file within ALOHA you can Exit Alt F4 choose between two modes Response Mode or Planning Mode Response Mode Choose this mode when you open a saved file in order to use ALOHA during a real emergency As ALOHA ope
198. osion 141 Chapter 4 Reference Percent Mass in Fireball When you model a BLEVE in ALOHA it is assumed that part or all of the chemical forms a fireball while the remainder burns as a pool fire You can choose to either a estimate the percent mass of chemical in the fireball or b enter the tank pressure or temperature and let ALOHA estimate the percent mass of the fireball BLEVE Percent Mass in Fireball BLEVE Fireball Scenario The higher the internal tank pressure or tank temperature at the time of tank failure the larger the fireball Any liquid not consumed by the fireball will form a pool fire Enter one of the following Percentage of mass in the fireball 20 2 100 100 C Pressure inside the tank at time of failure psia C mmHg C atm C Pa 68 1 C Temperature inside the tank at time of failure CF 283 6 degrees Cc Cancel If you know the tank pressure or temperature at failure enter either value and let ALOHA calculate the percentage of mass in the fireball However pressure and temperature are often difficult to determine If you don t know those values you can specify the percentage of mass in the fireball The percentage mass in the fireball must be greater than the minimum value supplied by ALOHA and no more than 100 Choosing 100 will usually give you the worst case scenario with the largest thermal radiation hazard Based on the pressure and temperature of the
199. ou will also need to enter the maximum puddle diameter or area Ground type influences the amount of heat energy transferred from the ground to an evaporating puddle Ground type is most important when the spilled liquid is cryogenic Cryogenic liquids such as refrigerated propane are liquids that are stored at very low temperatures because they boil at temperatures well below ambient As it estimates heat transfer from ground to puddle ALOHA assumes that the ground does not absorb any of the spilled chemical and that none of the chemical spilled onto water dissolves into the water 144 Chapter 4 Reference ALOHA offers you five choices for ground type Default soil unwetted soil not covered by rock or concrete Concrete concrete cement asphalt or otherwise paved surfaces Sandy dry soil Moist sandy soil Water lakes oceans or other large bodies of water Puddle Parameters Help Select ground type C Default soil select this if unknown Concrete Sandy dry soil C Moist sandy soil Water Input ground temperature Help Use air temperature select this if unknown C Ground temperature is 80 deg CFCC Input maximum puddle diameter or area Help Unknown C Maximum diameter C Maximum area ft C yds C meters Cancel Note For ground type descriptive terms like dry or moist refer to the state of the ground before the chemical was spilled that is the amount of water in the soil isf
200. oud dispersion For example you may respond to a release of a liquid from a storage tank originally running the release in ALOHA as a Tank source After an hour or so the tank may stop leaking but an evaporating puddle may have formed In such a case rerun the scenario in ALOHA as a Puddle source Later if the puddle becomes smaller in size as it evaporates or because it is being cleaned up or diked enter new values for its area and its volume mass or depth then rerun your Puddle scenario Whenever you use a SAM with ALOHA make sure that your computer s internal clock is set to the time and date of the release that you are modeling ALOHA uses time and date along with wind speed and cloud cover to choose stability class 127 Chapter 4 Reference Source In an ALOHA scenario the source is the vessel or pool from which a hazardous chemical is released The source strength is the rate at which the chemical enters the atmosphere or the burn rate depending on the scenario A chemical may escape very quickly so that source strength is high as when a pressurized container is ruptured or more slowly over a longer period of time so that source strength is low as when a puddle evaporates ALOHA can model four types of sources e Direct chemical release directly into the atmosphere bypassing ALOHA s source calculations e Puddle chemical has formed a liquid pool e Tank chemical is escaping from a storage tank e
201. ound Type and Initial Temperatures Next for evaporating puddles indicate the type of ground beneath the puddle Ground type influences the amount of heat energy transferred from the ground to an evaporating puddle Ground type is most important when the spilled liquid is cryogenic Cryogenic liquids such as refrigerated propane are liquids that are stored at very low temperatures because they boil at temperatures well below ambient As it estimates heat transfer from ground to puddle ALOHA assumes that the ground does not absorb any of the spilled chemical and that none of the chemical spilled onto water dissolves into the water ALOHA offers you five choices for ground type Ground Type Ground and Puddle Temperature e Default soil unwetted soil not covered by Select ground type Help rock or concrete Default soil select this if unknown C Concrete e Concrete concrete cement asphalt or C Sandy dry soil otherwise paved surfaces C Moist sandy soil Water e Sandy dry soil 4 Input ground temperature Help Moist sandy soil Use air temperature select this if unknown o i OF e e Water lakes oceans or other large bodies of cree ee tabecerer S72 Fee water Input initial puddle temperature Help PEAN 7 Use ground temperature select this if unknown Note For ground type descriptive terms like dry C Use air temperature or moist refer to the state of the ground before C Initial puddle temperature is 72 CF CC the chemical
202. oys several different models including an air dispersion model that it uses to estimate the movement and dispersion of chemical gas clouds From this model ALOHA is able to estimate the toxic gas dispersion the overpressure values from a vapor cloud explosion or the flammable areas of a vapor cloud ALOHA uses additional models to estimate the hazards associated with other fires and explosions ALOHA can solve problems rapidly and provide results in a graphic easy to use format This can be helpful during an emergency response or planning for such a response ALOHA originated as a tool to aid in emergency response It has evolved over the years into a tool used for a wide range of response planning and academic purposes However How accurate is ALOHA you must still rely on your own common sense and Keep in mind that ALOHA is only a experience when deciding how to respond to a particular incident There are features that would be useful in some of ALOHA s models in the dispersion model for example equations accounting for site topography that have not been included in ALOHA because they would require extensive input and computational time ALOHA s most important limitations are discussed later in this chapter tool Its usefulness depends on the accuracy of the information you enter into ALOHA and on your accurate interpretation of the data and how you apply it to each situation Introduction to dispersion modeling Many differ
203. pe Of Leak wvivissinscactuavasessesesiaceiacssasaatessaumsavevacdeuntetesaseavaenedeps 143 Height of the Tank Opening s seseseeessesseessessseessseessressereseeesesessseesseese 144 P ddl formatio sssini n a e a 144 Gas Pipe lime isis agin cea spiecave i oneen a a E T E EEE S ATE RA EE KEEA 146 Pipe Sorc PUES nonai oeie e EEEE EE ae ee ae 146 Source strength information in the Text Summary ssseeeeeeeereereeeereese 147 Calculation Options onceden nae enaa iiaa EREE Aa ATE 148 Display Ment icer i s Berei ii aa dite Sea dag dO 149 Threat Zone nien a a ah a a E E E a 149 Level Of Conee m i ssiisiimisissinissinatoiin nnna tia eee 150 Vapor Cloud Explosion Parameters eeseeeeeeseseeseeseeereeresressesererressessee 150 Threat Zone OC iirc e i a a A a E E aeneatae 152 Interpreting a threat Zone sssssesesesseeesseeeresressesseseresresreseresresseseresressesee 153 Displaying threat zones in other applications 00 0 0 eee eeeeeeeeeereeeeeeees 153 Threat Ab Pointiersin ns aceon eee anal ce lance cet amie ct sone Matos ied 153 Using fixed east west and north south coordinates 00 0 0 cee eeees 154 Using relative downwind and crosswind coordinates ce eeeeeeee 154 Threat at POU TESUtS nseni ner ean ae oe dst aod ne tne a tau 154 Text Summary imk ea E EEEE RETEA REA Sa aaas Seis 156 Table of Contents SOULCE Stren UN so o Bie lee eatin Ble E E aes us tana ead 156 Constant source SUPOU S Use ce ust cesar
204. played a hazard on a threat zone plot you can use the Threat at Point option to obtain specific information about the hazards at points of interest such as schools and hospitals in and around the threat zones The downwind distance along the centerline of a chemical cloud out to the level of concern that you set ALOHA s threat zone lengths reported in the Text Summary window are threat distances Area within which the hazard level toxicity flammability thermal radiation or overpressure is predicted to exceed your Level of Concern LOC at some time after a release begins You may specify up to three LOCs in ALOHA If three LOCs are chosen ALOHA will display the threat zones in red orange and yellow overlaid on a single threat zone plot By default the red zone represents the worst hazard A time dependent value is something that changes over time ALOHA s dispersion predictions account for release rates that change over time in this sense these predictions are time dependent However ALOHA does not account for changing atmospheric conditions when predicting dispersion in this sense its predictions are not time dependent A release rate that changes over time For example release rate from a pressurized tank declines over time as tank pressure drops 185 Glossary Two phase flow Unstable Upper Explosive Limit UEL Urban or Forest Vapor Both the liquid and gas phases of a chemical sometimes can
205. prevent you from inadvertently entering an unrealistic input value If you enter a value outside of the allowable range ALOHA will warn you and tell you what the limits are You must modify your value before ALOHA will continue Check ALOHA s on screen help topics for more information about ALOHA inputs 164 Chapter 5 Troubleshooting When I changed some atmospheric conditions ALOHA told me that it is unable to verify the consistency between my new atmospheric data and the source data Then I had to reset the source I set up a release scenario in ALOHA then started MARPLOT clicked on a location on my map and chose Set Source Point from the ALOHA menu in MARPLOT s Sharing menu But I don t see a threat zone on my map What s wrong My computer crashed while I had an ALOHA threat zone plotted on a map in MARPLOT Now whenever I reopen the map I see the old threat zone on the map and I can t delete it MARPLOT tells me that the ALOHA layer is locked I m running MARPLOT with ALOHA while I respond to a spill I m also using a SAM station to collect weather data I ve had a threat zone displayed in MARPLOT for the last half hour I know the wind has shifted direction but the threat zone hasn t changed at all What s wrong ALOHA s Puddle Tank and Gas Pipeline source strength calculations are affected by atmospheric conditions ALOHA recomputes source strength whenever possible after you have modified atmospheric
206. quid or solid to form a vapor evaporate The direction from which the wind is blowing For ALOHA s purposes a diagram displaying recent measurements of average wind speed and direction at a location when a SAM is used See Roughness length 187 Glossary 188 A accuracy 15 advection 16 AEGLs 44 169 aerosol definition of 169 heavy gas 17 jet fire 24 Tank source 137 air dispersion model 15 air exchange rate 105 air temperature 118 ALOHA basic organization 11 choosing a model 148 duration limits 129 help 14 limitations of 28 31 menu bar 13 purpose of 11 save files 100 ambient saturation concentration 109 anhydrous 170 Atmospheric menu item SAM Station 122 127 User Input 113 121 atmospheric stability definition of 170 very stable conditions 28 See also stability class atmospheric transmissivity 121 autoignition temperature 19 B blast force See overpressure blast wave See overpressure Index BLEVE explanation of 25 fireball 25 hazardous fragments 25 boiling point 171 Building Type menu item 104 105 air exchange rate 105 choice of building 104 surroundings 105 burning puddle See pool fire byproducts 31 C Calculation Options menu item 148 CAMEO 159 carcinogen 110 chemical adding to library 112 deleting from library 113 flammable and toxic 19 library ChemLib 107 mixtures 31 modifying library 112 properties needed table 111 r
207. r Input The first Atmospheric Options dialog box appears 2 The wind is travelling from the southwest at a speed of 7 miles per hour Type 7 in the wind speed box then select mph Type SW in the wind direction box 3 The wind conditions are measured at a height of 10 meters Select the tower icon in the Measurement Height section Notice that ALOHA has filled in a value of 10 meters 4 There are very few buildings in the industrial park and a large grassy field is located to the northeast the area where the wind would blow the toxic vapor cloud Select the Open Country ground roughness option Atmospheric Options Wind Speed is 7 C knots mph meters sec Help Wind is from SW Enter degrees true or text e g ESE Measurement Height above ground is Help A c a g A OR entervalue 10 tect eiT meters Ground Roughness is Open Country C Urban or Fores C Open Water Help OR C Input Roughness Zo Select Cloud Cover at 2 complete partly clear cover cloudy Help 03 OR enter value c A A 0 10 Cancel 5 The sky is more than half covered by clouds Under Select Cloud Cover choose the second option from the left the option between the complete cover and partly cloudy options Notice that ALOHA has filled in a value of 7 Click OK The second Atmospheric Options dialog box appears 51 Chapter 3 Examples 6 The air temperature is 80 F Type 80
208. r million ppm 181 patchiness concentration 30 pipe racks 27 planning mode 99 plume rise 181 plume 181 pool fire 24 pressure wave See overpressure Print menu items 100 puddle evaporation about 133 air temperature 118 cloud cover 118 sun angle 101 terrain 31 Puddle source 132 136 area and volume of 135 evaporating puddle 133 ground temperature 136 ground type 135 initial temperature 136 type of puddle 133 192 Index Q Quit menu item 100 R radioactive particles 31 rainout 181 release rate 130 Response Information Data Sheets 159 response mode 99 RIDS 159 roughness element 116 roughness length Zo 117 S SAM choosing a SAM 122 data codes 122 dialog boxes 124 radio frequency 123 serial port 123 sigma theta 126 transmitting data 122 troubleshooting 164 using during an incident 123 127 SAM Options menu about 124 Archive Data menu item 125 Processed Data menu item 126 Raw Data menu item 126 Wind Rose menu item 127 SAM Station menu item 122 127 Save and Save As menu items 100 save file definition of 182 opening 99 serial port 123 SetUp menu 107 149 Sharing menu 159 161 sheltered surroundings 105 shock wave See overpressure single storied building 105 SiteData menu 101 106 solubility 182 solution strength definition of 183 entering 108 solutions 183 Source about 128 Direct source 130 132 duration limits 129 Gas Pipe
209. ransportation routes and address ranges for street segments MARPLOT readable maps incorporating this TIGER information can be downloaded from the CAMEO download Web site http www epa gov oem cameo marmaps Check your MARPLOT manual for more information about obtaining and using maps Using MARPLOT When ALOHA and MARPLOT are running simultaneously ALOHA automatically installs a menu in MARPLOT s Sharing menu You can choose items from this menu to indicate the location of a release display an ALOHA threat zone plot on a MARPLOT map or indicate a location for which you would like specific hazard information Choose from among the following items contained in the ALOHA submenu e Help Choose Help to see a discussion about using MARPLOT together with ALOHA 160 Chapter 4 Reference e Set Source Point First click once on the location of an accidental chemical release on your MARPLOT map this is the source point Next Pon anai choose Set Source Point ALOHA will place a Help pink cross symbol at the source location Once a CAMEOFm Set Source Point threat zone has been displayed in ALOHA Set Threat Point hs ALOHA s threat zone as well as the wind direction confidence lines around it will Delete ALOHA Objects automatically be drawn on the map in MARPLOT If you already designated a Threat at Point in ALOHA that location will be marked by a blue crosshair mark on the map in MARPLOT Note If you are using an
210. ration will be low This property changes with temperature a liquid at a higher temperature will have a higher ambient saturation concentration A chemical that is a gas at ambient temperature and pressure has an ambient saturation concentration of 100 1 000 000 ppm Without water A chemical shipped or stored without water rather than in solution is in anhydrous form anhydrous ammonia is a common example A measure of the tendency of air to move upward or downward within the atmosphere generating turbulence The atmosphere may be more or less turbulent at any given time depending on the amount of incoming solar radiation as well as other factors Meteorologists have defined six atmospheric stability classes from A to F each representing a different degree of turbulence in the atmosphere When moderate to strong incoming solar radiation heats air near the ground causing it to rise and generating large eddies the atmosphere is considered unstable Unstable conditions are associated with atmospheric stability classes A and B air has a strong tendency to move up or down and the atmosphere is more turbulent When solar radiation is relatively weak or absent air near the surface has a reduced tendency to rise and less turbulence develops In this case the atmosphere is considered stable the wind is weak and the stability class would be E or F Stability classes D and C represent conditions of more neutral stability moderately turb
211. rations at any location of special Threat Zone Ctrl F concern during the hour after a release begins that s the threat at a point Threat At Point Ctri R Text Summary Ctrl k The Central Valley Elementary School is located about 1 500 yards Source Strength Ctri G downwind of the treatment plant You have already indicated the school s building type and degree of shelter from the wind Next you ll indicate Tile Windows the location of the school relative to the release point at the treatment Stack Windows plant Display Options Ctrl 1 Choose Threat At Point from the Display menu A Concentration Location dialog box appears 2 Click Relative Coordinates to indicate that you are describing the school s location in terms of its downwind and crosswind distance relative to the release point In other situations you might choose to describe the school s location in terms of geographic east west or north south distances Type 1500 in the downwind distance box then select yards Type 0 in the crosswind distance box When you enter a crosswind distance of 0 you re indicating that the wind is blowing the gas cloud directly towards the location of concern so that concentrations will be as high as possible ALOHA s concentration graph then represents the worst case prediction for the location Click OK Concentration Location Specify the location at which you want to evaluate the concentration over time Relative C
212. rature as well as liquid volume inside the tank as it leaks If the tank contains unpressurized liquid ALOHA assumes that gravity will drain the tank and that a puddle will form on the ground below the tank ALOHA cannot model a release in which there is both a pre existing puddle on the ground and liquid continuing to leak from a tank into the puddle If you encounter this situation and the puddle is still spreading choose Tank from the Source submenu to model the release as a tank leak If the puddle has reached or is about to reach its maximum size choose Puddle from the Source submenu to treat the release as a pre existing puddle Liquefied gases Both the liquid and gas phases of a chemical sometimes can escape together from a ruptured tank as a two phase flow Many substances that are gases under normal pressures and temperatures are stored under high enough pressures to liquefy them For example propane is a gas at normal pressures and temperatures but is often stored under pressure as a liquid When a rupture or broken valve causes a sudden pressure loss in a tank of liquefied gas the liquid boils violently the tank contents foam up and the tank fills with a mixture of gas and fine liquid droplets called aerosol When such a two phase mixture escapes from the container the release rate can be significantly greater than that for a purely gaseous release Note ALOHA does not model the release of a liquid that has an overpressure appli
213. ratures but it is being stored under pressure as a liquefied gas at ambient temperature the tank is not refrigerated in this scenario Select the Tank contains liquid option Check to be sure that Chemical stored at ambient temperature is selected Click OK A Liquid Mass or Volume dialog box appears Chemical Ctrl H Atmospheric gt Puddle Ctrl U Calculation Options Gas Pipeline Ctrl I N Tank Size and Orientation Select tank type and orientation Vertical cylinder Horizontal cylinder C Enter two of three values diameter 2 5 feet C meters length 6 8 diameter volume 250 gallons cu feet Cancel Help Chemical State and Temperature Enter state of the chemical Tank contains liquid C Tank contains gas only C Unknown Enter the temperature within the tank Chemical stored at ambient temperature C Chemical stored at 72 degrees 38 Chapter 2 Learning the Basics 4 The tank contains 1 ton 2 000 lbs of chlorine Select tons 2 000 Ibs then type 1 in the mass in tank box Notice that ALOHA fills in the other values Click OK An Area and Type of Leak dialog box appears Liquid Mass or Volume Enter the mass in the tank OR volume of the liquid C pounds The mass in the tankis tons 2 000 Ibs C kilograms OR Enter liquid level OR volume gallons a The liquid x C cubic feet volume is 170 C liters mi C cubic meters 67 9 full
214. re at Ambient Temperature 6 13 atm Ambient Saturation Concentration 134 835 ppm or 13 5 ATMOSPHERIC DATA MANUAL INPUT OF DATA Wind 7 miles hour from SW at 16 meters Ground Roughness open country Cloud Cover 7 tenths Air Temperature 86 F Stability Class D No Inversion Height Relative Humidity 75 SOURCE STRENGTH SELECT SOURCE 52 Chapter 3 Examples Describing the release Now you re ready to enter information about the release itself that is to set the source for this release 1 The benzene is leaking from a tank In the SetUp menu point to Source then select Tank A Tank Size and Orientation dialog box appears 2 The benzene is stored in a 500 gallon 4 foot diameter vertical tank Select Vertical cylinder Type 500 in the volume box then select gallons Type 4 in the diameter box then select feet Notice that ALOHA automatically calculates the tank length Click OK A Chemical State and Temperature dialog box appears Tank Size and Orientation Select tank type and orientation Vertical cylinder ce o 2 Enter two of three values diameter 4 length 5 32 feet C meters volume 500 gallons cu feet Cancel Help 3 The benzene is stored in the tank as a liquid notice in the Text Summary that it has a boiling point of 176 F well above the ambient temperature Select the Tank contains liquid option Check to be sure that Chemical stored at ambient temperature is
215. rength information in the Text Summary Regardless of the source option you choose once you have entered all necessary inputs and clicked OK on the last source strength dialog box ALOHA estimates source strength It then displays the source input values you entered and the results of its calculations in the Text Summary For example for non burning sources you might see the following information e Source type A brief description of the type of source modeled for example Flammable gas escaping from pipe not burning e Release duration The length of time in minutes during which the chemical is predicted to continue to escape into the atmosphere If ALOHA predicts the release to continue for more than an hour you ll see the message Release Duration ALOHA limited the duration to 1 hour e Total amount released This is the amount of chemical that ALOHA predicts will be released into the atmosphere during the hour after a release begins not the amount of liquid that spills from a tank during that time Review the information you have entered as it appears in the Text Summary to be sure that you made no errors when entering information Review the source type predicted release rate duration and total amount released to be sure that this information seems reasonable to you If it does not try to obtain more information about the release in order to more accurately model it 147 Chapter 4 Reference Calculation Options C
216. rger objects like a building can impede the flame front so they should not be considered obstacles for the purposes of congestion Greater turbulence allows the flame front to accelerate thereby generating a more powerful blast wave i e greater overpressure ALOHA uses two congestion levels congested and uncongested ALOHA s blast estimates are based on experiments that used a volume blockage ratio volume occupied by obstacles within the cloud divided by cloud volume of less than 1 5 for an uncongested cloud and greater than 1 5 for a congested cloud Estimating the level of congestion in a non laboratory setting is difficult but the following examples might be helpful Uncongested zones include parking lots open fields suburban neighborhoods and most urban environments Generally a congested zone has so many closely spaced obstacles that it is difficult or impossible to walk through it It is uncommon for this level of congestion to be found throughout the entire vapor cloud However pipe racks in industrial facilities and some forested areas where the trees and branches are closely spaced may be characterized as congested areas What role does confinement play in vapor cloud explosions Partial confinement can also increase the severity of the explosion In general a vapor cloud is considered partially confined when walls ceilings or other extended surfaces keep the cloud from moving freely For example an open sided parkin
217. rm a pool fire The amount of the chemical involved in the fireball and or the pool fire will depend on the conditions at the time of release The primary hazards associated with a BLEVE are thermal radiation overpressure hazardous fragments smoke and toxic byproducts from the fire ALOHA can help you model the thermal radiation hazard When you use the Tank source with a nonflammable chemical ALOHA will x Scenario automatically select the leaking tank not Tank containing an unpressurized flammable liquid burning option and the toxic gas output the only options for a nonflammable chemical Although both flammable and nonflammable liquefied gases can be involved in BLEVEs ALOHA only C BLEVE tank explodes and chemical burns in a fireball models flammable liquid BLEVEs Type of Tank Failure Type of Tank Failure Leaking tank chemical is not burning and forms an evaporating puddle C Leaking tank chemical is burning and forms a pool fire Potential hazards from flammable chemical which is not burning as it leaks from tank If you choose either of the first two Downwind toxic effects scenarios you will need to enter Vapor cloud flash fire information about the type of leak beginning with the Area and Type of Leak dialog box If you choose the BLEVE scenario you may need to enter information about the fireball in the ol BLEVE Percent Mass in Fireball dialog box Overpressure blast force from vapor cloud expl
218. rocedures Washington D C Federal Emergency Management Agency Publications Office Havens Jerry and Tom Spicer 1990 LNG Vapor Dispersion Prediction with the DEGADIS Dense Gas Dispersion Model Topical Report April 1988 July 1990 Chicago Gas Research Institute Lees Frank P 1980 Loss Prevention in the Process Industries Vol 1 London and Boston Butterworths Lees Frank P 2001 Loss Prevention in the Process Industries Vol 2 Second edition New Delhi Butterworth Heinemann Leslie I R M and A M Birk 1991 State of the art review of pressure liquefied gas container failure modes and associated projectile hazards Journal of Hazardous Materials 28 3 329 365 National Institute for Occupational Health and Safety NIOSH U S Department of Health and Human Services DHHS 2005 NIOSH Pocket Guide to Chemical Hazards NIOSH Publication No 2005 149 Online version and ordering information at http www cdc gov niosh npg Lists TLVs permissible exposure limits PELs and IDLH values as well as general industrial hygiene information for 677 chemical substances 167 Bibliography U S Environmental Protection Agency EPA the Federal Emergency Management Agency FEMA and the U S Department of Transportation DOT 1987 Technical Guidance for Hazards Analysis Emergency Planning for Extremely Hazardous Substances 1987 Download a PDF copy from http yosemite epa gov oswer ceppoweb nsf content consolidatedPub
219. rogram icon located in the ALOHA folder 2 Read the list of ALOHA s limitations click Help to see more details then click OK 3 Select Location from the SiteData menu A Location Information dialog box appears with a list of the names of cities included in ALOHA s location library 49 Chapter 3 Examples 4 The industrial park is located outside Baton Rouge Louisiana Type the characters ba to quickly move to the section of the list containing names beginning with ba Scroll down a little farther until you see BATON ROUGE LOUISIANA Click on this name to highlight it then click Select Location Information BAKERSFIELD CALIFORNIA BALTIMORE MARYLAND BARNWELL SOUTH CAROLINA BARSTOW CALIFORNIA Cancel BATAVIA ILLINOIS BATAVIA NEW YORK aa BATON ROUGE LOUISIANA BEAUMONT TEXAS BEAVERTON OREGON Modify BELLEVILLE ILLINOIS BENSON NORTH CAROLINA BERKELEY CALIFORNIA Delete BILLINGS MONTANA BIRMINGHAM ALABAMA BISMARCK NORTH DAKOTA hd Help In this example you will not modify the default building type settings because you will not assess indoor concentration at specific locations 5 Select Date amp Time from the SiteData menu A Date and Time Options dialog box appears 6 The release occurs at 10 30 p m on August 20 2006 Select the Set a constant time option Enter the month day year hour and minute for this scenario press Tab to move from one box
220. roll through the list of states and territories Loekie i Me a until you see Virginia You can also Cancel Help click anywhere within the list then type v to quickly move to that letter s location in the list Click on Virginia Click OK ALOHA s list of locations will reappear 85 Chapter 3 Examples 6 Click on MANASSAS VIRGINIA to highlight it then click Select Location Information LOS GATOS CALIFORNIA LOUISVILLE COLORADO LOUISVILLE KENTUCKY LOVELAND COLORADO MACON GEORGIA MADISON WISCONSIN MADISONVILLE KENTUCKY MANCHESTER IOWA Modify MANCHESTER NEW HAMPSHIRE MANHATTAN KANSAS MANSFIELD MASSACHUSETTS Delete MANSFIELD OHIO rs MARIETTA GEORGIA MARQUETTE MICHIGAN Help In this example you will not modify the default building type settings because you are only interested in outdoor concentrations 7 Select Date amp Time from the SiteData menu A Date and Time Options dialog box appears 8 The release occurs at 3 p m 1500 in 24 hour time on June 4 2006 Select the Set a constant time option Enter the month day year hour and minute for this scenario press Tab to move from one box to the next Click OK Date and Time Options You can either use the computer s internal clock for the model s date and time or set a constant date and time C Use internal clock Seta constant time Input a constant date and time Month Day Year Hour Minute 1 12 1
221. rs an ignition source the cloud can catch fire and burn rapidly in what is called a flash fire Possible hazards associated with a flash fire include thermal radiation smoke and toxic byproducts from the fire ALOHA will predict the flammable area of the vapor cloud that is the area where a flash fire could occur at some time after the release The lowest temperature at which a liquid gives off enough vapor to be ignited at its surface The sudden vaporization of a liquid This occurs most often when a chemical is a gas at standard temperature and pressure but is stored as a liquid under pressure If the storage container ruptures the sudden reduction in pressure can cause the liquid to boil violently flash boil and the tank contents to foam up filling the tank with a two phase mixture of gas and liquid See Threat zone Also melting point The temperature at which the solid and liquid phases of a substance exist in equilibrium The freezing point depends on the chemical composition and the applied pressure The normal freezing point is defined at a pressure of 1 atmosphere For example the normal freezing point of water is 0 C 32 F 175 Glossary Fuel reactivity Fumes Gas es Gaussian GMT A characteristic of a chemical that rates the tendency of the flame front to accelerate when a vapor cloud burns The reactivity ratings are related to the speed of the flame front when there is no turbulence
222. ructural damage 0 50 1 0 Windows usually shattered some window frame damage 0 70 Minor damage to house structures 1 0 Partial demolition of houses made uninhabitable 1 0 2 0 Corrugated metal panels fail and buckle Housing wood panels blown in 1 0 8 0 Range for slight to serious laceration injuries from flying glass and other missiles 2 0 Partial collapse of walls and roofs of houses 2 0 3 0 Non reinforced concrete or cinder block walls shattered 2 4 12 2 Range for 1 90 eardrum rupture among exposed populations 2 5 50 destruction of home brickwork 3 0 Steel frame building distorted and pulled away from foundation 5 0 Wooden utility poles snapped 5 0 7 0 Nearly complete destruction of houses 7 0 Loaded train cars overturned 9 0 Loaded train box cars demolished 10 0 Probable total building destruction 14 5 29 0 Range for the 1 99 fatalities among exposed populations due to direct blast effects These are peak pressures formed in excess of normal atmospheric pressure by blast and shock waves 22 Chapter 1 Welcome to ALOHA Hazardous fragments One of the major hazards associated with any explosion is flying debris hazardous fragments propelled by the explosion s pressure wave Hazardous fragments come from two primary sources container fragments and debris from the surrounding area ALOHA does not model the hazardous fragments threat If an explosion is likely to occur first responders must be aware of the possi
223. ry voltage in volts ALOHA does not place a limit on the amount of data you may archive To stop data archiving choose End Archive Data from the SAM Options menu You can then open and view the file in any word processing program To view the most recently transmitted SAM data without interrupting data archiving select either Raw Data or Processed Data from the SAM Options menu 125 Chapter 4 Reference Raw Data Choose Raw Data from the SAM Options menu to examine the most recently transmitted unprocessed SAM data ALOHA displays unprocessed SAM data in the same format in which it is transmitted from the SAM Raw Sam Data 999 1 52 32 85 5 91 15 81 1 39 26 17 15 75 12 3 24 Checksum f 5 g E Q e 2 Sigma theta degrees gt Vector mean wind speed meters per second gt Mean wind direction degrees true gt Mean air temperature degrees Celsius gt Instantaneous wind speed meters per second oo Instantaneous wind direction degrees true gt Remaining SAM battery voltage volts gt Instantaneous air temperature degrees Celsius gt Processed Data Choose Processed Data from the SAM Options menu to view processed weather data including the most recently transmitted instantaneous readings as well as 5 minute running averaged values in a new Processed SAM Data window If ALOHA cannot interpret and process the data that it receives from your
224. s 140 Chapter 4 Reference Type of Tank Failure When you use the Tank source with a flammable chemical ALOHA will ask you to specify the type of release Select one of these three options e Leaking Tank Not Burning If a flammable chemical escapes from a tank and does not immediately burn either the chemical will go directly into the air or it may form an evaporating puddle depending on the storage conditions In either case a flammable vapor cloud will form ALOHA can predict three possible hazardous outcomes the toxic area of the vapor cloud the flammable area of the vapor cloud where igniting the cloud would cause a flash fire and the overpressure blast force from a vapor cloud explosion e Leaking Tank Burning When a flammable liquid forms a burning puddle it is called a pool fire When a flammable gas or an aerosol two phase flow burns as it sprays from an opening in a tank it is called a jet fire Based on the storage conditions you specified ALOHA will decide whether to model the chemical as a pool fire or a jet fire Potential hazards associated with a pool fire or jet fire include thermal radiation smoke and toxic byproducts from the fire ALOHA can help you model the thermal radiation hazard e BLEVE Boiling Liquid Expanding Vapor Explosion When a tank containing a liquefied gas fails completely a BLEVE can occur Some of the released chemical will burn in a fireball while the remainder will fo
225. s e Terrain and e Hazardous fragments Byproducts from fires explosions or chemical reactions ALOHA doesn t account for the byproducts of combustion e g smoke or for chemical reactions ALOHA assumes that a dispersing chemical cloud does not react with the gases that make up the atmosphere such as oxygen and water vapor However many chemicals react with dry or humid air water other chemicals or even themselves Because of these chemical reactions the chemical that disperses downwind might be very different from the chemical that originally escaped from containment In some cases this difference may be substantial enough to make ALOHA s dispersion predictions inaccurate For example if aluminum phosphide escapes from containment and comes in contact with water the reaction between the water and aluminum phosphide produces phosphine gas It is the phosphine rather than the aluminum phosphide that escapes into the atmosphere If you respond to such an accident and wish to use ALOHA to obtain a threat zone estimate you need to estimate how rapidly phosphine is being generated from the reaction between water and aluminum phosphide and you need to model the incident in ALOHA as a release of phosphine rather than aluminum phosphide Particulates ALOHA does not account for the processes that affect dispersion of particulates including radioactive particles Chemical mixtures ALOHA is designed to model the release of pure chemical
226. s BLEVEs Flammable Areas where a Flash Fire could occur and Vapor Cloud Explosions Each is described on the following pages Often more than one kind of fire and or explosion is possible ALOHA helps you by listing the kinds of fires and explosions that are possible given your release scenario Chemical releases involving a fire and or an explosion can be complicated in that an initial incident may trigger other fires and explosions in the surrounding area The trigger may be an increase in temperature an open flame or a container punctured by debris from the initial fire or explosion Throughout this manual the term fires and explosions will be used to describe situations where there may be a combination or a series of fires and or explosions 23 Chapter 1 Welcome to ALOHA Jet fires A jet fire also referred to as a flame jet occurs when a flammable chemical is rapidly released from an opening in a container and immediately catches on fire much like the flame from a blowtorch ALOHA can model a jet fire from the Gas Pipeline and Tank sources For the Tank source ALOHA can model gas and two phase jet fires A two phase jet fire occurs when a gas that has been liquefied under pressure is released Because the liquid evaporates as it escapes the chemical is released as an aerosol spray that is a mixture of gas and tiny liquid droplets ALOHA assumes the jet fire release is oriented vertically although the wind can tilt
227. s s 1 115 663 2 45 187 3 Dy 92 4 18 57 5 13 40 6 11 30 8 20 10 5 14 12 4 11 Note The durations that correspond to effects like pain or second degree burns can vary considerably depending on circumstances The effects above were observed on bare skin that was exposed directly to the thermal radiation Some types of clothing can serve as a protective barrier against thermal radiation and can affect the exposure duration However exposure duration should be kept to a minimum even at low levels of thermal radiation 20 Chapter 1 Welcome to ALOHA What is an explosion The most basic definition of an explosion is a sudden intense release of energy that often produces a loud noise high temperatures and flying debris and generates a pressure wave There are many types of explosions and the causes and effects will vary ALOHA primarily models explosions that are the result of accidents involving industrial chemicals Intentional explosions will generally but not always result in greater hazard damage Consider three primary hazards when dealing with an explosion thermal radiation overpressure and hazardous fragments flying debris All three of these hazards are not present in every explosion and the severity of the hazard will depend on the explosion These hazards typically last only for a brief period directly following the explosion However it is important to consider the potential for secondary explo
228. s and some chemical solutions It s difficult for any model to correctly predict the behavior of a solution or a mixture of chemicals because it s difficult to accurately predict chemical properties such as vapor pressure for solutions or mixtures ALOHA s predictions are greatly affected by this and other chemical properties When an incorrect property value is used in ALOHA the model s release rate and dispersion estimates will not be valid Terrain ALOHA expects the ground below a leaking tank or puddle to be flat so that the liquid spreads out evenly in all directions It does not account for pooling within depressions or the flow of liquid across sloping ground Hazardous fragments Ifa chemical release involves an explosion there will be flying debris from the container and the surrounding area ALOHA does not model the trajectories of the hazardous fragments 31 Chapter 1 Welcome to ALOHA 32 Learning the Basics This chapter contains a step by step ALOHA example a toxic gas dispersion scenario describing a chlorine release at a fictional treatment plant in South Dakota Follow along using your own copy of ALOHA in order to familiarize yourself with its menus and features For more information about any aspect of ALOHA go to the Reference chapter Guided tour The Central Water Facility treatment plant is located in a rural area about 2 miles from Sioux Falls South Dakota The plant uses 1 ton containers of chlor
229. s htm Describes step by step procedures for hazards analysis recommends and discusses use of one tenth of the IDLH as the Level of Concern for Extremely Hazardous Substances in emergency planning Spicer Tom and Jerry Havens 1989 User s Guide for the DEGADIS 2 1 Dense Gas Dispersion Model EPA 450 4 89 019 Cincinnati U S Environmental Protection Agency Turner D Bruce 1994 Workbook of Atmospheric Dispersion Estimates An Introduction to Dispersion Modeling Second edition Boca Raton Florida Lewis Publishers Turner D Bruce and Lucille W Bender 1986 Description of UNAMAP Version 6 Springfield Virginia National Technical Information Service Wilson D J 1987 Stay indoors or evacuate to avoid exposure to toxic gas Emergency Preparedness Digest 14 1 19 24 Woodward V L 1998 Estimating the Flammable Mass of a Vapor Cloud New York Center for Chemical Process Safety American Institute of Chemical Engineers 168 AEGLs Aerosol Air dispersion model Air exchange rate ALOHA Glossary Acute Exposure Guideline Levels AEGLs are Toxic Levels of Concern LOCs that you can use in ALOHA to predict the area where a toxic gas concentration might be high enough to harm people The AEGLs are under development by the National Research Council s National Advisory Committee on AEGLs AEGLs take into account sensitive individuals and are meant to protect nearly all people As of October 2005 the final AEGL val
230. s of the chemical in the tank this should be the total mass of the liquid and its vapor in the tank Type the volume of the liquid in the tank and indicate its units Type your best estimate of the percent of the tank volume that is taken up by liquid as full by volume or Use the scroll bar next to the tank diagram to indicate the approximate height of the liquid level in the tank Scroll up or down to position the horizontal bar on the diagram to indicate the liquid height If possible check for a condensation line on the outer tank wall to get an estimate of the liquid level within the tank Liquid Mass or Volume Enter the mass in the tank OR volume of the liquid pounds The mass in the tankis tons 2 000 Ibs C kilograms OR Enter liquid level OR volume n gallons The liquid S cubic feet E volume is 1170 liters mi cubic meters 67 9 full by volume z Cancel Help 139 Chapter 4 Reference Gas in a tank Whenever you indicate to ALOHA that a tank contains only gas by clicking Tank contains gas only when you are asked to identify chemical state you will need to type either the tank pressure or the amount of gas in the tank Mass or Pressure of Gas Enter either tank pressure OR amount of gas mmHg sat atm The tank pressure is 6 C psia C Pa OR C pounds C tons 2000 Ibs The amount of gas is 206 S akilograms C cu ft at STP C cum at STP Help Type
231. s than ALOHA s indoor concentration line indicates Text Summary Select Text Summary from the Display menu to bring the Text Summary window forward when other ALOHA windows appear in front of it ALOHA s Text Summary contains information about the scenario you are working on Review its contents to see summaries of e Information that you have entered into ALOHA e Some basic properties of the chemical you have selected e Results of ALOHA s calculations e Messages indicating the information that you still need to enter and e Additional notes describing any special circumstances that may exist The Text Summary window remains open whenever ALOHA is running Review its contents periodically as you prepare a scenario to ensure that you have entered model inputs correctly and to check the results of ALOHA s calculations Choose New from the File menu when you want to clear existing Text Summary information before beginning a new scenario Source Strength Choose Source Strength from the Display menu to see either the rate at which the chemical enters the atmosphere or the burn rate depending on the scenario When you choose this menu item ALOHA displays a graph showing the rate source strength predicted for the first hour after a release begins or until the release is complete whichever is shortest Note ALOHA does not display a source strength graph for BLEVE scenarios ALOHA produces two main types of source strength estimates
232. se a SAM Archive Data with ALOHA Instead use them when you want to view or archive weather R i Raw Data information collected by the SAM Processed Data Wind Rose 124 Chapter 4 Reference Archive Data Choose Archive Data from the SAM Options menu to create a tab delimited text file containing data from the SAM along with dates and times of transmissions You will be asked to name the archive file Type in a file name then click Save ALOHA then creates this file for you as it receives SAM data adding data each time it receives new information from the SAM Data are arranged in columns and rows within the archive file The first three lines in the file contain an explanation of units and the date and time when the data were collected The fourth line contains the column headings as follows Hr Min Sec ID mW S mDir SigTh mTemp iW S iDir iTemp BatVol Table 4 7 Translation key for SAM column headings Column Heading Required Information Hr Hours Min Minutes Sec Seconds ID Station identification number mW S Vector mean wind speed in meters per second mDir Mean direction in degrees true SigTh Sigma theta standard deviation of the wind direction in degrees mTemp Mean air temperature in degrees Celsius iW S Instantaneous wind speed in meters per second iDir Instantaneous direction in degrees true iTemp Instantaneous temperature in degrees Celsius BatVol Instantaneous SAM batte
233. select Topics from the Help menu When the list appears click any topic name to view a discussion of that topic When you ve finished reading about that topic click Contents to return to the list of topics When you are ready to go back to using ALOHA close or minimize the Help window On a Macintosh To see the list of help topics select Topics from the Help menu When the list appears highlight a topic name then click Select to view a discussion of that topic When you ve finished reading the help topic click a Topics to return to the list 0 Cancel to close the window c Copy to copy the help text to the clipboard or d Print to print the help text How to use this manual This manual includes five chapters Begin here in Chapter 1 by reviewing a discussion of basic concepts Turn to Chapter 2 for a step by step ALOHA tutorial Chapter 3 contains ALOHA example problems Turn to Chapter 4 for descriptions of the main features of ALOHA Sections in this chapter include explanations of each of ALOHA s menus along with background information to help you to better understand ALOHA s computations Review Chapter 5 for trouble shooting advice At the back of the manual you ll find a bibliography a glossary and an index Note Terms displayed in italics are defined in the glossary 14 Chapter 1 Welcome to ALOHA Modeling in ALOHA ALHOA models three hazard categories toxic gas dispersion fires and explosions ALOHA empl
234. sions and fires to occur before deciding that these hazards no longer exist Overpressure A major hazard associated with any explosion is overpressure Overpressure also called a blast wave refers to the sudden onset of a pressure wave after an explosion This pressure wave is caused by the energy released in the initial explosion the bigger the initial explosion the more damaging the pressure wave Pressure waves are nearly instantaneous traveling at the speed of sound Although a pressure wave may sound less dangerous than a fire or hazardous fragments it can be just as damaging and just as deadly The pressure wave radiates outward like a giant burst of air crashing into anything in its path generating hazardous fragments If the pressure wave has enough power behind it it can lift people off the ground and throw them up against nearby buildings or trees Additionally blast waves can damage buildings or even knock them flat often injuring or killing the people inside them The sudden change in pressure can also affect pressure sensitive organs like the ears and lungs The damaging effects of the overpressure will be greatest near the source of the explosion and lessen as you move farther from the source When you use ALOHA to predict an explosion s effects assess the surroundings at the explosion site as you interpret ALOHA s threat zone plot Large objects like trees and buildings in the path of the pressure wave can affect its stren
235. sk you to specify whether you want to model an evaporating puddle or burning puddle pool fire before you can enter any details about the puddle e Evaporating Puddle As a flammable puddle evaporates it forms a vapor cloud above the puddle ALOHA can predict three possible hazardous outcomes the toxic area of the vapor cloud the flammable area of the vapor cloud where igniting the cloud would cause a flash fire and the overpressure blast force from a vapor cloud explosion e Burning Puddle Pool Fire When a flammable puddle catches on fire it is called a pool fire Potential hazards associated with a pool fire include thermal radiation smoke and toxic byproducts from the fire ALOHA can help you model the thermal radiation hazard Type of Puddle Scenario Puddle of a flammable chemical Type of Puddle Evaporating Puddle C Burning Puddle Pool Fire Potential hazards from flammable chemical evaporating from puddle Downwind toxic effects Vapor cloud flash fire Overpressure blast force from vapor cloud explosion Cancel When you use the Puddle source with a nonflammable chemical ALOHA will automatically select the evaporating puddle option and the toxic gas output the only options for a nonflammable chemical Evaporating Puddle To model evaporation from a puddle ALOHA accounts for the effects of wind speed atmospheric turbulence air temperature and pressure viscosity and other properties of the
236. spilled chemical It accounts for the effects on puddle temperature of solar heating evaporative cooling and several other ways in which heat is exchanged between a puddle and its environment For example on a sunny day ALOHA will expect heat energy from the sun to warm the puddle It expects puddle temperature to directly influence evaporation rate so that the higher the puddle temperature the faster the evaporation rate ALOHA accounts for changes in puddle temperature and therefore evaporation rate over time 133 Chapter 4 Reference What if the weather conditions change Bear in mind that wind speed and air temperature are important influences on evaporation rate If these conditions change after ALOHA has estimated an evaporation rate enter the new values and rerun ALOHA The types of heat transfer that ALOHA expects to affect puddle temperature fall into the following three categories e Incoming solar radiation affected by location time and date and cloud cover e Heat transfer with the air affected by air temperature humidity and initial puddle temperature and e Heat transfer with the ground affected by ground temperature ground type and initial puddle temperature soe Evaporative radiation ris loss Ground conduction Figure 4 3 Factors influencing ALOHA s puddle evaporation estimates ALOHA can model evaporation from puddles that are either boiling or that are cooler than the boili
237. sq m 2nd degree burns within 66 sec Yellow 1231 yards 2 6 kW sq m pain within 66 sec 73 Chapter 3 Examples Modeling a second scenario flash fire or vapor cloud explosion Now that ALOHA has displayed the thermal radiation hazard from a BLEVE you want to assess the threat if the tank leaks and a flammable vapor cloud forms instead If this situation occurs either a flash fire or a vapor cloud explosion could occur depending on the scenario specifics For both of these scenarios you will need to begin by estimating the flammable area of the vapor cloud You do not need to enter new information for time atmospheric conditions or tank size 1 When you run multiple scenarios for the same incident the plots and Text Summary screen from the first scenario will change when you enter new information Before you start running an additional scenario either print out the threat zone plot and the Text Summary screen or paste them into a word processing document You ll need the original information to compare the scenarios later Close the threat zone plot window When you set the source for the first scenario you told ALOHA that a BLEVE occurred You need to return to the Type of Tank Failure screen and tell ALOHA that now you want to model a scenario where the chemical is not burning as it escapes into the atmosphere Begin by selecting the Tank source again In the SetUp menu point to Source then select Tank A Ta
238. ss C No Inversion Height Relative Humidity 86 SOURCE STRENGTH Direct Source 456 pounds Source Height 6 Release Duration 1 minute Release Rate 7 5 pounds sec Total Amount Released 456 pounds Note This chemical may flash boil and or result in two phase flow THREAT ZONE Model Run Heavy Gas Red 1484 yards 26 ppm AEGL 3 66 min Orange 1 9 miles 2 ppm AEGL 2 66 min Yellow 3 1 miles 6 5 ppm AEGL 1 66 min 91 Chapter 3 Examples Using MARPLOT Now you are ready to plot ALOHA s threat zone estimates on a map of the area in MARPLOT and to obtain a concentration estimate for the workmen s location 1 Select Go to Map from the MARPLOT submenu under ALOHA s Sharing menu to start MARPLOT About Shared Menus Edit Shared Menus CAMEOFm gt MARPLOT gt Help Go to Map 2 If this is the first time you ve used MARPLOT a dialog box may appear directing you to browse to the location of your MARPLOT application Once MARPLOT is located ALOHA will automatically open MARPLOT Click OK on the opening screen If this is the first time you ve used MARPLOT the Prince William County VA map should automatically be displayed If it is not then select Go to View from MARPLOT s View menu A Go to View dialog box appears 3 Click to highlight lt entire map gt Prince William County VA then click Go to View lt entire map Prince William County VA sort by name C sort b
239. ssa feat eh ee tee tet 157 Variable source strengthens inair 157 Source strength AVerA RING 52 3 ys elias aes ee ae toh eee ands 158 Tile and Stack WANA O WS 1 5 ant ei cld innen a a A a 158 Display Options scncnn Rated ccietneta cesar econ n iiie een ee 158 Sharine Ment saie ae aes lab A a ED a ead ee ee as 159 Items in the Sharing Menu ry on a sh ran ated aaa ee ct ene atest ae 159 CAMEO MON sipncatisncesstuvnnesetiies anseletsnges E E a A T R AA 159 MARPLOT Menu ai E cee eee ee A EATE E ee ie 160 Usina MARPLO Tere a a a a E a a 160 Chapter 5 Troubleshooting sssssssessesssoessosesosessoeeo 163 BiblOg raphy 4s coco resien e ea i OS aaa a s 167 GIOSSATY Orn care E A se ee ate eae Ee ed OE AE E eee E 169 Index Sct oectwia ed engen ian Wir r aE eae nd ease eee sae ees 189 10 Welcome to ALOHA Welcome to ALOHA This chapter contains an overview of ALOHA an explanation of how to use this manual and ALOHA s on screen help and a discussion of basic concepts About ALOHA Program purpose ALOHA Areal Locations of Hazardous Atmospheres is a computer program designed especially for use by people responding to chemical releases as well as for emergency planning and training ALOHA models key hazards toxicity flammability thermal radiation heat and overpressure explosion blast force related to chemical releases that result in toxic gas dispersions fires and or explosions Note In versions prior to 5 4 AL
240. sumed to form a fireball which includes both the chemical that flash boiled and the chemical that was sprayed out as an aerosol during the explosion The remaining liquid forms a pool fire When ALOHA models a BLEVE situation including both a fireball and a pool fire it estimates the thermal radiation from both fires it is not necessary to run an additional Pool Fire scenario Area and Type of Leak You must indicate the shape circular or rectangular and size of the Area and Type of Leak Select the shape that best represents the shape of opening in the leaking tank before ALOHA can the opening through which the pollutant is exiting calculate the rate of release of the tank s contents You also must specify whether the release is wets through a a simple hole in the tank wall or b a pees short pipe or broken valve A hole is any kind of Circular opening C Rectangular opening break in the tank wall such as a puncture or crack inches The area of an opening is important to ALOHA but Arar os feet A pening diameter z its shape is used only to compute area ALOHA C centimeters predicts identical release rates through circular and Mose rectangular openings if they have the same area Is leak through a hole or short pipejvalve Hole Short pipejvalve If your scenario is a release of pure gas from the tank when you click OK ALOHA will estimate Cancel Heip the rate of release of gas from the tank You will see a su
241. sure As pressure increases the boiling point of a substance also increases The boiling point is also the temperature at which the vapor pressure of a liquid is equal to the applied atmospheric pressure The normal boiling point is the temperature at which a liquid under 1 atmosphere of pressure boils The ambient boiling point is the temperature at which the chemical boils at the ambient pressure The length of time that a flammable substance burns ALOHA limits burn duration to 1 hour The fraction of the sky that is obscured by clouds ALOHA uses a scale in which cloud cover is measured in tenths for example when half the sky is covered by clouds the cloud cover is 5 tenths 171 Glossary Concentration Concentration patchiness Congestion Conservative Continuous source Crosswind Cryogenic The amount of a chemical present in a given weight or volume of air In ALOHA concentration of a gas in air is expressed in units such as parts per million by volume or milligrams per cubic meter Distribution of a pollutant gas as patches of high and low concentration Especially near the source of a release wind eddies push a pollutant cloud unpredictably about causing gas concentrations at any moment to be high in one location and low in another ALOHA does not account for concentration patchiness near the point of a release A concept used to quantify the way small structures within the vapor cloud affect
242. surrounding area and create additional debris The container fragments and other debris hazardous fragments are swept up in the explosion and rapidly propelled by the explosion over a wide area ALOHA does not model the dispersion of hazardous fragments or overpressure blast force ina BLEVE If a BLEVE is likely to occur first responders must take the necessary precautions to protect themselves and others from the overpressure and hazardous fragments 25 Chapter 1 Welcome to ALOHA Flash fires flammable area When a flammable vapor cloud encounters an ignition source the cloud can catch fire and burn rapidly in what is called a flash fire Potential hazards associated with a flash fire include thermal radiation smoke and toxic byproducts from the fire ALOHA will predict the flammable area of the vapor cloud that is the area where a flash fire could occur at some time after the release The flammable area is bounded by the Lower Explosive Limit LEL and the Upper Explosive Limit UEL These limits are percentages that represent the concentration of the fuel that is the chemical vapor in the air If the chemical vapor comes into contact with an ignition source it will burn only if its fuel air concentration is between the LEL and the UEL because that portion of the cloud is already pre mixed to the right mixture of fuel and air for burning to occur If the fuel air concentration is below the LEL there is not enough fuel
243. surroundings 105 Chapter 4 Reference Date amp Time Choose Date amp Time from the SiteData menu to specify the date and time for ALOHA to use Rate and dime Options You can either use the computer s internal clock for the model s date and time or set a constant date and time as the starting time of your scenario You may choose either to enter a specific time or to have ALOHA take the time from your computer s internal clock When you use the internal clock option you will need to set your Internal Clock Time is computer s clock to the local time where a Tue Dec 12 08 56 14 2006 release has occurred For example if you are running ALOHA in Seattle for an incident taking place in Miami set your clock to the current Miami time Use internal clock C Seta constant time The starting time of a scenario affects ALOHA s calculations in two ways 1 ALOHA uses the scenario start time to determine whether it is night or day when choosing a stability class and 2 ALOHA uses the position of the sun at the scenario start time to estimate incoming solar radiation Solar radiation can be an important influence on puddle evaporation Whenever you use your computer s clock the scenario starting time will be updated to the current time whenever you enter atmospheric information change location or choose the Date amp Time menu item To specify date and time choose Date amp Time from the SiteData menu then sel
244. t English units and ALOHA s computation results will be displayed in those units When running ALOHA you can choose either type of units but for this example English units have been selected Click OK Display Options Select Output Units English units C Metric units Choosing LOCs and creating a threat zone plot 1 Choose Threat Zone from the Display menu A Hazard To Analyze dialog box appears 58 Chapter 3 Examples As the puddle evaporates a vapor cloud forms ALOHA can help you model three possible hazardous scenarios for the flammable vapor cloud toxic area flammable area or blast area For this example you want to display the toxic area on a threat zone plot Select the Toxic Area of Vapor Cloud option Click OK A Toxic Level of Concern dialog box appears Hazard To Analyze Scenario Flammable chemical escaping from tank Chemical is NOT on fire Choose Hazard to Analyze Toxic Area of Vapor Cloud C Flammable Area of Vapor Cloud C Blast Area of Vapor Cloud Explosion ALOHA uses ERPGs Emergency Response Planning Guidelines as the default LOCs for benzene so you ll keep the default LOCs and check that Show confidence lines only for the longest threat zone has been selected Click OK ALOHA will display a threat zone plot for this release Toxic Level of Concern Select Toxic Level of Concern Red Threat Zone Loc IEA Orange Threat Zone Loc ERPG 2 150 ppm Yellow Thr
245. t 1 500 yards downwind of the treatment plant In ALOHA this feature is called the Threat at Point Using on screen ALOHA help As you use ALOHA you ll enter information on a series of dialog boxes to describe your scenario On most dialog boxes you ll see at least one Help button which you can use to access on screen help Click any of these buttons at any time to view an explanation of the ALOHA feature you re using or input value that you must enter into the model To return to the dialog box once you ve finished reading the help information a with Microsoft Windows close or minimize the Help window or b on a Macintosh click Cancel to exit from the on screen help 33 Chapter 2 Learning the Basics Describing the time and place Your first tasks are to start ALOHA and then describe the time and place of the scenario i Start ALOHA In Windows click the Start button point to Programs then choose the ALOHA item On a Macintosh double click the ALOHA program icon located in the ALOHA folder Read the list of ALOHA s limitations click Help to see more details then click OK Select Location from the SiteData menu A Location Information dialog box appears with a list of the names of cities included in ALOHA s location library Location Ctri L r Building Type The treatment plant is located 2 miles from Sioux Falls South Dakota Type the characters si to quickly move to SIOUX FALLS Date
246. t is for toxic gas dispersions flash fire flammable areas and vapor cloud explosions Select items from the SetUp menu in descending order as you describe a scenario first select Chemical then Atmospheric and finally Source Chemical Ctrl H Atmospheric gt User Input Ctrl 4 Source gt SAM Station Calculation Options Chemical Ctrl H Atmospheric gt Calculation Options Pudia iia Tank Ctrl T Gas Pipeline Ctrl I Chemical Select Chemical from the SetUp menu to access a list of the chemicals included in ALOHA s chemical library ChemLib Physical property and toxicological data for about 1 000 pure chemicals are included in the library ALOHA uses the information in the library to predict how a particular chemical may escape from a container and disperse in the atmosphere The library does not include any chemical mixtures chemicals with unstable structures or chemicals of such low volatility and toxicity that they don t represent air dispersion hazards that is solids or liquids with very low vapor pressures that present a toxic hazard only when present at high concentrations The library does contain a small number of solutions You can add pure chemicals to the library or delete chemicals from it and you can modify information about the physical properties of any pure chemical Note You cannot view or modify properties that were obtained from the proprietary Design Institute for Physical Properti
247. t least 1 minute For burn rates ALOHA averages over timesteps lasting 20 seconds Choose Source Strength from the Display menu to see a graph of these averaged rate s for a particular scenario To save calculation time ALOHA uses these averaged release rate s to make its threat zone estimates The Maximum Average Sustained Release Rate or the Maximum Burn Rate if applicable is the highest of these averaged release rates It is represented by the tallest timestep on the Source Strength graph When a gas or liquid escapes from a pressurized container the release rate may drop very quickly sometimes within seconds as the pressure within the container drops In such cases the initial release rate may be much higher than the maximum average release rate When you re using a SAM ALOHA recomputes its threat zone and threat at a point estimates each time it receives new weather data from a SAM However it does not recompute source strength when it receives new data During prolonged incidents because time of day and weather conditions may have important effects on source strength especially from an evaporating puddle be sure to periodically update ALOHA s source strength calculations Direct source In the SetUp menu point to Source then select Direct Choose the Direct source option if you know the amount of pollutant gas released directly or evaporated or if you have too little information about a release to use another source opti
248. tank at storage ALOHA calculates the minimum amount of mass that would have gone into the fireball if the container failed at the storage conditions Note If all of the mass goes into the fireball at storage conditions ALOHA will automatically use 100 and skip this dialog box ALOHA displays the allowable range above the percentage mass in fireball value box The amount of chemical in the fireball will depend upon the pressure inside the tank when it ruptures As the chemical is heated the internal pressure in the tank increases the higher the temperature the higher the pressure and the greater the size of the fireball Properly functioning relief valves may help limit the tank pressure and the size of the fireball 142 Chapter 4 Reference Both the nature of the chemical and the tank construction affect the size of the fireball Tanks holding liquefied gases are designed to withstand high pressures and therefore pose a greater risk of a BLEVE For typical propane tanks the internal tank pressure under normal storage conditions is already high enough that 100 of the released chemical would form a fireball no pool fire would form While flammable liquids are typically stored in vessels less capable of withstanding high internal pressures fireballs have been generated by the heat induced rupture of such tanks When you model a BLEVE in ALOHA three times the amount of the flammable chemical that flash boils during the BLEVE is as
249. the Text Summary for this release Text Summary SOURCE STRENGTH Leak from hole in vertical cylindrical tank Flammable chemical is burning as it escapes from tank Tank Diameter 4 feet Tank Length 5 32 feet Tank Volume 566 gallons Tank contains liquid Internal Temperature 86 F Chemical Mass in Tank 1 82 tons Tank is 166 full Circular Opening Diameter 6 inches Opening is 16 inches from tank bottom Max Puddle Diameter Unknown Max Flame Length 26 yards Burn Duration 2 minutes Max Burn Rate 1 616 pounds min Total Amount Burned 3 682 pounds Note The chemical escaped as a liquid and formed a burning puddle The puddle spread to a diameter of 15 6 yards THREAT ZONE Threat Modeled Thermal radiation from pool fire Red 36 yards 16 6 kW sq m potentially lethal within 66 sec Orange 51 yards 5 6 kW sq m 2nd degree burns within 66 sec Yellow 78 yards 2 6 kW sq m pain within 66 sec 64 Chapter 3 Examples Compare the threat zone plots and the Text Summary screens from both of the scenarios The threat distances from the Text Summary screens are summarized in a table below The origin 0 0 on both plots represents the center of the puddle ALOHA estimates that the red toxic threat zone the worst hazard level extends primarily in the downwind direction for about 82 yards The worst of the thermal radiation threat the red zone is predicted to extend roughly 30 yards in all directions and a
250. the flames in the downwind direction Thermal radiation is the primary hazard associated with a jet fire Other potential jet fire hazards include smoke toxic byproducts from the fire and secondary fires and explosions in the surrounding area although ALOHA does not model these hazards In some cases heat from the jet fire may weaken the tank and cause it to fail completely in which case a BLEVE may occur Typically a BLEVE poses a greater threat than a jet fire If the chemical inside the tank is likely to BLEVE for example if the tank contains a liquefied gas in addition to modeling the scenario as a jet fire you should also rerun the scenario as a BLEVE to compare the size of the threat zones Pool fire A pool fire occurs when a flammable liquid forms a puddle on the ground and catches on fire ALOHA only models pool fires on land it does not model pool fires on water Thermal radiation is the primary hazard associated with a pool fire Other potential pool fire hazards include smoke toxic byproducts from the fire and secondary fires and explosions in the surrounding area although ALOHA does not model these hazards In some cases heat from the pool fire may weaken a leaking tank and cause it to fail completely in which case a BLEVE may occur Typically a BLEVE poses a greater threat than a pool fire If the chemical inside the tank is likely to BLEVE for example if the tank contains a liquefied gas you may want to mod
251. the overpressure hazard from a vapor cloud explosion you want to assess the thermal radiation threat if the tank leaks and the escaping propane is quickly ignited so that a jet fire occurs instead Therefore you do not need to enter new information for time atmospheric conditions or tank size 1 The source strength information Either print out the threat zone plot and the Text Summary screen from the last scenario or paste them into a word processing document You ll need the information to compare the scenarios later Close the threat zone plot window When you set the source for the second scenario you told ALOHA that the tank was leaking but the chemical was not on fire You need to return to the Type of Tank Failure screen and tell ALOHA that now you want to model a scenario where the chemical is burning as it escapes into the atmosphere Begin by selecting the Tank source again In the SetUp menu point to Source then select Tank A Tank Size and Orientation dialog box appears Your original information is still correct on the Tank Size and Orientation Chemical State and ipa es a pressurized flammable liquid Temperature and the Liquid Mass or Volume dialog boxes Click OK on each screen until the Type of Tank Failure dialog box appears Type of Tank Failure Type of Tank Failure C Leaking tank chemical is not burning as it escapes into the atmosphere Leaking tank chemical is burning as a jet fire C BLEVE ta
252. timates that the puddle reached a maximum diameter of 21 7 yards Flammable chemical escaping from tank not burning Tank Diameter 4 feet Tank Volume 566 gallons Tank contains liquid Chemical Mass in Tank 1 82 tons Circular Opening Diameter 6 inches Opening is 16 inches from tank bottom Ground Type Concrete Ground Temperature equal to ambient Max Puddle Diameter Unknown Release Duration 46 minutes Tank Length 5 32 feet Internal Temperature 86 F Tank is 166 full Max Average Sustained Release Rate 77 2 pounds min averaged over a minute or more Total Amount Released 3 682 pounds Note The chemical escaped as a liquid and formed an evaporating puddle The puddle spread to a diameter of 21 7 yards 56 Chapter 3 Examples 9 Choose Source Strength from the Display menu to see the source strength graph for this scenario The graph shows the predicted averaged release rate during the hour after the release begins Source Strength Evaporation Rate pounds minute 80 minutes Whenever you run ALOHA ask yourself Is ALOHA accurately representing what is actually occurring in this scenario In this case liquid benzene leaks from a tank to form a puddle ALOHA expects that because the puddle is undiked it spreads out to cover a large area and evaporates at a high rate for a relatively short period of time What if the puddle were constrained by small depressions in the ground Th
253. ting cannot be used Select building type or enter exchange parameter in fire and explosion scenarios You first must specify the C Enclosed office building Help building type of concern which could be either the type of Single storied building building that is most common in the area downwind of the aoei release point or the type that you are most concerned soe ls BBB about Indicate whether the building is single or double Select building surroundings Hep storied or is an enclosed office building You also must C Sheltered surroundings trees bushes etc indicate whether it is relatively sheltered or unsheltered Unsheltered surroundings from the wind by trees buildings or other obstacles to the ned wind ALOHA expects pollutant concentrations to build up faster within single storied rather than double storied buildings and faster within unsheltered rather than sheltered buildings 104 Chapter 4 Reference To estimate indoor pollutant concentration ALOHA first estimates the building s air exchange rate that is the number of times per hour that the volume of air within the building is completely replaced by new outdoor air when doors and windows are closed This rate is less than 1 0 if it takes more than an hour to completely change the air within the building You also can choose to enter a value for air exchange rate rather than specifying a building type if you have this information To estimate infiltration rate
254. to be heavy Flash boiling and two phase flow Many substances that are gases under normal pressures and temperatures are stored under pressures high enough to liquefy them For example propane is a gas at normal pressures and temperatures but is often stored under pressure as a liquid When a tank rupture or broken valve causes a sudden pressure loss in a tank of liquefied gas the liquid boils violently and the tank contents foam up filling the tank with a mixture of gas and fine liquid droplets called aerosol Flash boiling is the term for that sudden vaporization of a liquid caused by a loss of pressure When the liquid and gas phases of a chemical escape together from a ruptured tank the release is called a two phase flow When a two phase mixture escapes from storage the release rate can be significantly greater than that for a release of pure gas The two phase mixture that escapes into the atmosphere may behave like a heavy gas cloud The cloud is heavy in part because it is initially cold and therefore denser than it would be at ambient temperatures and also because it consists of a two phase mixture The tiny aerosol droplets mixed into the cloud act to weigh the cloud down and make it denser than a pure gas cloud and their evaporation cools the cloud 17 Chapter 1 Welcome to ALOHA ALOHA can choose a dispersion model for you ALOHA can automatically choose whether to predict the dispersion of a chemical as a Gaussian or he
255. to extend more than one and a half miles downwind and the yellow AEGL 1 threat zone is predicted to extend for more than two miles P Toxic Threat Zone gt 20 ppm AEGL 3 60 min gt Z ppm AEGL 2 60 min gt 0 5 ppm AEGL 1 60 min Confidence Lines Dashed lines along both sides of the yellow threat zone indicate uncertainty in the wind direction The wind rarely blows constantly from any one direction Each time it shifts direction it blows a pollutant cloud in a new direction The uncertainty lines around the longest threat zone enclose the region within which about 95 percent of the time the gas cloud is expected to remain Review the Text Summary You ll see the line of text Model Run Heavy Gas informing you that ALOHA used the heavy gas model to make its threat zone estimate Because the initial cloud of chlorine is heavier than air ALOHA models it as a heavy gas rather than as a gas that is about the same weight as air Text Summary THREAT ZONE Model Run Heavy Gas Red 1124 yards 26 ppm AEGL 3 66 min Orange 1 7 miles 2 ppm AEGL 2 66 min Yellow 2 8 miles 6 5 ppm AEGL 1 66 min 45 Chapter 2 Learning the Basics Determining threat levels at a specific location You can use ALOHA not only to estimate the extent of the area that could be at risk in an incident that s the threat zone but also to obtain Display predicted indoor and outdoor concent
256. to the next ALOHA requires you to convert the time of day into 24 hour time click Help to learn how to convert time values Click OK Date and Time Options You can either use the computer s internal clock for the model s date and time or set a constant date and time C Use internal clock Seta constant time Input a constant date and time Month Day Year Hour Minute 1 12 1 31 1900 0 23 0 59 Cancel Help 50 Chapter 3 Examples 7 To choose the chemical that is being released benzene select Chemical from the SetUp menu A Chemical Information dialog box appears with a list of the chemicals in ALOHA s chemical library 8 Select Pure Chemicals at the top of the window this should be the default Find BENZENE in the list type the character b to locate benzene more rapidly in the list click on this name then click Select Entering weather information Chemical Information View Pure Chemicals C Solutions Cancel ARSINE BENZALDEHYDE BENZENE BENZENESULFONYL CHLORIDE BENZONITRILE Add BENZOTRICHLORIDE BENZOTRIFLUORIDE BENZOYL CHLORIDE BENZYLAMINE BENZYL BROMIDE BENZYL CHLORIDE BENZYLIDENE CHLORIDE BIS 2 CHLOROETHOXY METHANE Modify Delete Help Now that you ve selected the location time and chemical you must provide information about weather conditions and ground roughness 1 Inthe SetUp menu point to Atmospheric then select Use
257. ud Flammable Area of Vapor Cloud Local areas of flame can occur even though the average concentration is below the LEL ALOHA finds the flammable area by using 60 of the LEL Blast Area of Vapor Cloud Explosion 76 Chapter 3 Examples 3 Keep ALOHA s default LOCs and check that Show confidence lines only for the longest threat zone has been selected Click OK ALOHA will display a threat zone plot for this release Flammable Level of Concern Select Flammable Level of Concern Red Threat Zone Loc LRAUUUN item a Ee iy X Orange Threat Zone LOC Yellow Threat Zone LOC 2 000 ppm 10 LEL Show confidence lines only for longest threat zone for each threat zone Cancel You ll see ALOHA s threat zone plot for this scenario showing two flammable threat zones The red threat zone represents the estimated flammable area where a flash fire or a vapor cloud explosion could occur at some time after the release begins ALOHA estimates that the red threat zone will extend 171 yards in the downwind direction The yellow threat zone represents the estimated area where propane concentrations could exceed 10 LEL a level often used by responders Flammable Threat Zone 200 300 yards gt 12 000 ppm 60 LEL Flame Pockets gt 2 000 ppm 10 LEL Confidence Lines 77 Chapter 3 Examples Check the Text Summary for this release Text Summary THREA
258. ues for more than 20 chemicals have been released interim AEGL values for more than 60 additional chemicals have also been established and proposed AEGL values for more chemicals are under review The committee s objective is to define AEGLs for the 300 extremely hazardous substances listed in Title III of the Superfund Amendment and Reauthorization Act the U S Environmental Protection Agency offers an online list of these substances AEGL Web site http www epa gov oppt aegl index htm Fine liquid droplets or solid particles suspended in a gas A computer model that predicts the movement and dispersion of a gas in the atmosphere The number of times per unit time that the volume of air within a building is completely replaced by new outdoor air when doors and windows are closed Usually expressed as number of air changes per hour ALOHA stands for Areal Locations of Hazardous Atmospheres ALOHA is a registered trademark of the U S Government 169 Glossary Ambient saturation concentration Anhydrous Atmospheric stability The maximum concentration of vapor that could be attained in the air in a closed space above a liquid at ambient temperature and pressure If a chemical has a high ambient saturation concentration it has a strong ability to displace air and the concentration of the chemical s vapor in the air above the liquid will be high If it has a low ambient saturation concentration the vapor concent
259. uge Louisiana a 500 gallon 4 foot diameter vertical tank contains liquid benzene On August 20 2006 at 10 30 p m local time a security guard discovers that liquid is leaking out of the tank through a 6 inch circular hole located 10 inches above the bottom of the tank He also sees that the liquid is flowing onto a paved area in the industrial park The guard thinks that the tank has just been filled that evening The temperature on scene is 80 F with the wind from the southwest at 7 miles per hour as measured at a height of 10 meters by a fixed meteorological tower at the site The sky is more than half covered by clouds and the humidity is about 75 percent A thunderstorm is approaching from the southwest There is no low level inversion There are very few buildings in the industrial park and a large grassy field is located to the northeast of the industrial park The Local Emergency Planning Committee has requested that on scene responders use ERPG 2 concentrations to define the toxic endpoints in their analysis of benzene hazards In this example scenario you ll determine 1 Distance to the ERPG 2 level if the puddle evaporates and forms a toxic vapor cloud and 2 Thermal radiation threat if the puddle is ignited by a lightning strike and forms a pool fire Choosing a location and a chemical 1 Start ALOHA In Windows click the Start button point to Programs then choose the ALOHA item On a Macintosh double click the ALOHA p
260. ulent Neutral conditions are associated with relatively strong wind speeds and moderate solar radiation 170 Glossary BLEVE Boiling point Burn Duration Cloud cover BLEVE stands for Boiling Liquid Expanding Vapor Explosion BLEVEs typically occur in closed storage tanks that contain a liquefied gas usually a gas that has been liquefied under pressure Although both flammable and nonflammable liquefied gases may be involved ina BLEVE ALOHA only models flammable liquid BLEVEs A common BLEVE scenario happens when a container of liquefied gas is heated by fire increasing the pressure within the container until the tank ruptures and fails When the container fails the chemical is released in an explosion If the chemical is above its boiling point when the container fails some or all of the liquid will flash boil that is instantaneously become a gas If the chemical is flammable a burning gas cloud called a fireball may occur if a significant amount of the chemical flash boils ALOHA assumes that any liquid not consumed in the fireball will form a pool fire Potential BLEVE hazards include thermal radiation overpressure hazardous fragments smoke and toxic byproducts from the fire The maximum temperature at which a substance s liquid phase can exist in equilibrium with its vapor phase Above the boiling point a liquid vaporizes completely The boiling point depends on a chemical s composition and the applied pres
261. uters can round off numbers differently as they make their calculations This can have a visible effect on ALOHA s source and dispersion estimates 166 Bibliography American Conference of Governmental Industrial Hygienists ACGIH 2004 2004 TLVs and BEIs ACGIH http www acgih org Most recent annual list of threshold limit values TLVs and biological exposure indices BEIs for several hundred chemical substances also discusses how these values were derived and how to interpret them American Institute of Chemical Engineers AIChE 1994 Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions Flash Fires and BLEVEs New York Center for Chemical Process Safety Brutsaert Wilfried 1982 Evaporation into the Atmosphere Theory History and Applications Boston D Reidel Publishing Company Committee on Toxicology National Research Council 2000 to present Acute Exposure Guideline Levels for Selected Airborne Chemicals Multiple volumes Washington D C National Academy Press http www nap edu Presents Acute Exposure Guideline Levels AEGLs describes AEGL development process and data used for each AEGL value Design Institute for Physical Property Data 2006 DIPPR Database of Evaluated Process Design Data Described at http dippr byu edu Federal Emergency Management Agency U S Department of Transportation and U S Environmental Protection Agency 1988 Handbook of Chemical Hazard Analysis P
262. volving a flammable and toxic chemical the area encompassed by the toxic threat zone will be greater than the threat zones associated with fire and explosion scenarios It is essential that you evaluate all of the scenario options before developing your response plan What is a fire A fire is a complex chain reaction where a fuel combines with oxygen to generate heat smoke and light Most chemicals fires will be triggered by one of the following ignition sources sparks static electricity heat or flames from another fire Additionally if a chemical is above its autoignition temperature it will spontaneously catch on fire without an external ignition source There are several properties that measure how readily that is how easily a chemical will catch on fire Here we ll discuss three of these properties volatility flash point and flammability limits Volatility is a measure of how easily a chemical evaporates A flammable liquid must begin to evaporate forming a vapor above the liquid before it can burn The more volatile a chemical the faster it evaporates and the quicker a flammable vapor cloud is formed The flash point is the lowest temperature where a flammable liquid will evaporate enough to catch on fire if an ignition source is present The lower the flash point the easier it is for a fire to start Flammability limits called the Lower Explosive Limit LEL and the Upper Explosive Limit UEL are the boundaries of the fl
263. w Threat Zone Loc 1 0 psi shatters glass S Show confidence lines only for longest threat zone for each threat zone Cancel ALOHA s threat zone window appears None of the LOCs were exceeded for the given scenario so ALOHA does not create a threat zone plot A vapor cloud explosion generating a dangerous overpressure is not likely to occur with the settings you chose for this scenario The cloud could still burn as a flash fire but it would not generate a dangerous blast wave In fact there are only a few chemicals in ALOHA s chemical library that have a high enough fuel reactivity to result in a vapor cloud explosion when the cloud is ignited by a spark or flame in an uncongested area Acetylene Ethylacetylene Ethylene oxide Hydrogen Propylene oxide and 1 3 Propylene oxide A vapor cloud explosion is more likely to occur if the area is congested or if the cloud was ignited by a detonation e g by a high power explosive device Now you will model the explosion for a congested area Overpressure Blast Force Threat Zone Threat Modeled Overpressure blast force from vapor cloud explosion Type of Ignition ignited by spark or flame Level of Congestion uncongested Model Run Heavy Gas Red LOC was never exceeded 8 0 psi destruction of buildings Orange LOC was never exceeded 3 5 psi serious injury likely Yellow LOC was never exceeded 1 0 psi shatters glass 9 Either print out
264. x appears Area and Type of Leak Select the shape that best represents the shape of the opening through which the pollutant is exiting CF wes lt length gt Circular opening Rectangular opening inches Opening length 40 C feet Opening width 0 1 C centimeters C meters Is leak through a hole or short pipe valve Hole C Short pipe valve Cancel Help Since you are modeling this scenario in order to plan for a potential release you don t know where the hole might occur However a hole that occurs at the bottom of the tank will give the worst case estimate for this type of scenario because the weight of the remaining propane in the tank will push the propane through the hole faster Type 0 in the of the way to the top of the tank box Click OK Height of the Tank Opening The bottom of the leak is 0 Cin ft C cm Cm above the bottom of the tank lig level OR of the way to the top of the tank Help 75 Chapter 3 Examples The source strength information that you have entered and the results of ALOHA s source strength calculations appear in the Text Summary ALOHA estimates that the release lasts for about 26 minutes and that the Maximum Average Sustained Release Rate is 5 730 pounds per minute Text Summary SOURCE STRENGTH Leak from hole in horizontal cylindrical tank Flammable chemical escaping from tank not burning Tank Diameter 9 0
265. y map Z Map List Cancel je Help l resize map window to fit view 92 Chapter 3 Examples The Prince William County map will then be displayed MARPLOT Prince William County VA DBR File Edit view List Objects Sharing Help v Focus Pt 38 48 49 N 77 39 08 W v1 in 7 55 mi 4 Now you ll search on the map for the location where the accident occurred Choose Search from the List menu A Search Criteria dialog box appears 93 Chapter 3 Examples 5 The workmen are working at the intersection of Gallerher Road with Lee Highway To search for Gallerher Road type GALL in the box next to the search have names that start with box Make sure that Individual Layer has been selected in the menu just below the Layer s to search heading then select Roads from the pulldown menu below that Check to be sure that Maps in View is selected in the menu below the Map s to search heading Click Search A Search Collection dialog box appears Search Criteria Search for objects that have names that start with gt GALL Layer s to search Map s to search Individual Layer z Maps in View x Roads x Cancel Help replace previous collection 6 The search collection includes three roads Click once on Gallerher Rd to highlight it then click Intersections An Intersections dialog box appears Search Collection Number of objects in collection 3 O
266. ylight savings when necessary ALOHA knows which states are located in each U S time zone However 11 U S states extend across more than one time zone When you add a 9 E new city in any of these states to ALOHA s city library you may need to indicate the time zone in which the city Sagal is located if it is close to a boundary between time zones If the city is not located near a time zone boundary ALOHA will not display this dialog box States with multiple time zones are Idaho Indiana Kansas Kentucky Michigan Nebraska North Dakota Oregon South Dakota Tennessee and Texas Central or Eastern Time Zone Select time zone for city C Central Once you ve clicked OK the name of the new location should appear highlighted in the location list To save your information and select the location from the list click Select If you click Cancel now the information about the location that you just entered will not be added to the location library and the city name will be removed from the list Adding a location outside the U S Choose Location from the SiteData menu to access the list of locations Click Add In the dialog box that appears type in the name of the location Don t include its country name you ll be asked for that later Select Not in U S Type the location s approximate elevation latitude and longitude then click OK Location Input Enter full location name Location is j Hamilton Is location in a
267. your chosen duration However in most releases the rate will change over time For example if a chemical escapes from a pressurized tank or gas pipeline its release rate may decline rapidly as storage pressure drops If possible you should choose either the Tank or Gas Pipeline source option Both account for rate changes over time and will result in more accurate threat zone estimates Once you have entered all of the required information you can set your LOCs and view the threat zones for the vapor cloud For flammable chemicals you can view the 1 toxic area 2 flammable area and 3 blast area if a vapor cloud explosion occurs For nonflammable chemicals you can view the toxic threat zones Direct release of gas into the atmosphere Begin by selecting the source strength units You can use units of either weight or volume If you use volume units you must complete a second dialog box where you will specify whether the chemical is a gas or liquid and enter its storage temperature ALOHA then converts volume to mass to make its source strength computations Next indicate whether the release is instantaneous lasting one minute or continuous lasting more than one minute If a release is continuous type its duration in minutes ALOHA has a maximum duration of 60 minutes Direct Source Select source strength units of mass or volume Help C grams C kilograms pounds C tons 2 000 Ibs C cubic meters C liters C cubic feet ga

ALOHA® - the Oklahoma Department of Environmental Quality

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ALOHA® - the Oklahoma Department of Environmental Quality