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Local Exhaust Ventilation (LEV)

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1. Local Exhaust Ventilation LEV Guidance HEALTH AND SAFETY AUTHORITY Peo eo A eet Our vision A country where worker Safety nealth and welfare and the safe management of cnemicals are central to successful enterprise Published in January 2014 by the Health amp Safety Authority The Metropolitan Building James Joyce St Dublin 1 Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Drawings pictures diagrams courtesy of the HSE HSL UK amp IOSH OAY oo occ ag edes aaa a e aeae aa Ge ERANRR RNRRRRENERRNERENEKENEEKENK 2 A OCWICUOR oo coc ds szasa da oe sa ESEK es 4 FOR ASSESS ION Ls ose oo es oso akt ae 5 COMO a oo occ seta a a ak aa A 5 E E inas Elan LEV 0 ee ee cece eee Tres oi ocal E Nae E ccc c cence eee 19 I UISCOMMCEIO A Ne een anna 31 ate ito Alaon COMGIMINANTS 0c cece bb 55 o REMESAS 38 ne see e Eai Ventilation WEY anonser 40 Pete leteon arc A a OPEV 0 ec cece 43 m n On ancl aning t r EMPB GYSES aeaaeae 47 KERONO PECE ocea ase KATE ee 49 BARN AIAC MO MUON ING PEMONMANCS ys 0 5 5 ee cece cece eee ee 50 van Lecell RESUMES A ene e eve egek ket ree s SARGAS esrar s cole 666 a E 61 PEENES oo 58S a a a e S SES 62 Farine Re 63 US Contact e 5 yee cee eee
2. 5um particles 50 8um particles 100 1to 50um 80 to 99 5 to 10um 99 gt 5um 96 1to 5um 20 to 80 Advantages Efficiency increases as dust cake builds on fabric Efficient for large particles Minimum pressure drop Effective in high temperature and corrosive conditions Effective with hot gases corrosives Eliminates explosion hazards Disadvantages Flow resistance increases with dust build up Abrasives Cause Weal Less effective for smaller particles High cost Large equipment Requires specialist maintenance Noise Corrosion Biological fouling not an issue in caustic or acid scrubbers HEALTH AND SAFETY AUTHORITY Type Packed tower scrubber Air cleaner thermal oxidation incineration or flare HEALTH AND SAFETY AUTHORITY Filtering Efficiency Advantages Disadvantages High level surface Effective for water Noise contact for reaction miscible soluble materials Corrosion Biological fouling not an issue in caustic or acid scrubbers For gases or vapours Effective in destroying Not suitable for solids gases and vapours Voltage control box Cleaned air out Dirty air in Collector plates Dust Electrode collection wires hopper Chapter 4 27 28 Chapter 4 Clean air outlet Fabric filler Shaker motor Dirty air inlet Fan and motor assembly Dirty air Dust storage inlet
3. 2m approx AH Cleaned air out Dirty air swirls around outside of chamber throwing off dust Dust falls into collection hopper A AA HEALTH AND SAFETY AUTHORITY Air mover The fan is the most commonly used air mover that powers the extraction system The fan can be of a number of types 1 Centrifugal most commonly used for LEV system Generates large pressure differences and produces air flows against considerable resistance 2 Propeller more often used for general ventilation and usually not suitable where there is pressure resistance i e in line filter 3 Axial not suitable for dusts and cannot overcome pressure resistance Compressed air driven air movers can be used for specific tasks where electrically powered fans are unsuitable or where there are flammable gases They have high running costs low performance rates and high noise levels Fans Axial Fans Centrifugal lt lt Cased Axial Belt dirven axial Bifurcated axial least efficient but useful for flammable and corrosive materials e Good for high volume low resistance air movement as in general ventilation e Good for high resistance e Often used for smaller volumes e Backward curved blades are better h HEALTH AND SAFETY AUTHORITY Chapter 4 29 Discharge This releases the extracted air to a safe place It is crucial that exhausted air whether cleaned scrubbed or not is vent
4. Evaluation Authorisation and Restriction of Chemicals REACH Many enterprises that manufacture or use chemical substances have duties under the EU REACH regulation See www hsa ie and http echa europa eu information on REACH REACH impacts on a wide range of companies across many sectors In general REACH covers a number of roles including a manufacturer or downstream user Companies that use chemical substances have a duty to use them in a safe way and information on intended use and risk management measures RMMs including LEV needs to be passed up and down the supply chain through Safety Data Sheets SDSs containing exposure scenarios A BA HEALTH AND SAFETY Chapter 13 57 AUTHORITY Safety Health and Welfare at Work General Application Regulations 2007 S I No 299 of 2007 and as amended The term general application in the title of the Regulations is intended to convey that the various parts and chapters of the Regulations apply to all employments as does the Safety Health and Welfare at Work Act 2005 The Regulations place obligations as regards safety and health on employers employees and others They apply to all workplaces They lay down a basis for managing safety and health and ensuring that employers consult with employees on safety and health matters The Safety Health and Welfare at Work General Application Regulations 2007 contain 8 parts as follows Part 2 Workplace and use of work equipmen
5. 45 AUTHORITY If no records are available e g a commissioning report a competent ventilation engineer or occupational hygienist can assist to determine the effectiveness of the system and what measures are needed for adeguate control Maintenance checks may increase the potential for exposure to contaminants e g dirty filters and entry into confined spaces Maintenance measures should be risk assessed before being carried out Maintenance records should be kept from year to year to demonstrate ongoing effectiveness of the system and to assist in determining any deterioration by way of comparison with previous results Maintenance must be carried out by a person who is competent in the operation of the LEV system Any deficiencies found during system monitoring should be rectified to ensure the LEV is effective when in use and these interventions modifications should be included in LEV records Where maintenance work involves any entry into a confined space consult the HSA Code of Practice for Working in Confined Spaces see www hsa ie under publications A o AL 46 Chapter 9 HEALTH AND SAFETY AUTHORITY AE OA Info The employee using the LEV system should receive sufficient training so that they use the system effectively Training should be specific and deal with the actual system in place The employee should e understand the elements of the system and how they work e understand how to use the system effectiv
6. 5 eet ae a 64 O ons ca ceo 55 208 05 sas oo GS aoe a ae 65 Chapter 1 This guidance is written for employers managers employees and their safety representatives and those who provide install and maintain local exhaust ventilation LEV systems In preventing exposure to harmful substances in the workplace there is a hierarchy of control measures that must be considered commencing with the elimination or substitution of the hazard or where these options are not possible the hazard must be controlled by engineering means Local exhaust ventilation LEV is one such engineering control measure LEV is an engineering system designed to reduce employee exposure to airborne contaminants dust mist fume vapour gas in the workplace by capturing the emission at source and transporting it to a safe emission point or to a filter scrubber Employers need to work with designers suppliers installers and employees to effectively control exposure to airborne contaminants Suppliers must provide LEV that is fit for purpose is shown to work and continues to work The employer the LEV owner must ensure controls are adequate Everyone including suppliers and users of the LEV must be competent in the use of the LEV system The main LEV elements are e A hood of some kind where the contaminants enter the system e Ducting which safely transports the contaminants to a filter cleaner exhaust point Air cleaner filter scrubber e Air m
7. amount of ducting and whether the necessary conditions for fire are present For a fire to occur there must be 1 a fuel a combustible or flammable material and 2 oxygen as supplied by air in the ducting These two ingredients must be mixed in a sufficient ratio range flammable combustion explosion lower or upper limits LEL or UEL to initiate and sustain a fire Fuel can vary from flammable solvent vapour to grain or wood dust To initiate a fire a source of ignition is necessary A static discharge or a spark or friction heat from moving parts may be sufficient to initiate a fire To prevent a fire break the fire triangle there should be sufficient air flow through the ducting to prevent an accumulation of fuel such as wood dust settling out within the ducting and also avoid the generation of a fuel air mixture within a flammable range Bonding and earthing may be necessary to prevent static build up and regular maintenance will prevent friction heat and sparking thereby eliminating such sources of ignition Corrosives Corrosive substances may corrode the various components of the LEV system and render it ineffective by short circuiting the air flow damaging the filtering process or impairing the fan rotors Corrosion damage will cause loss of control reduction in performance and may cause exposure to employees This can become a less obvious concern where processes and materials change and the LEV is now being used not as ori
8. biological safety cabinets A AA HEALTH AND SAFETY Chapter 6 37 AUTHORITY Chapter 7 The ability of a local exhaust ventilation system to reduce exposure to air contaminants is determined primarily by the effectiveness of the hood s Ensure they are provided with sufficient air flow to contain and capture contaminants also verify the ability of the fan and ducting to extract sufficient air from each hood Flow rates can vary depending on the work being done For example a glove box or fully enclosed system needs sufficient flow to maintain it under a negative pressure with a relatively small flow rate within it However a relatively higher flow rate is reguired when the hood is capturing fugitive contaminants especially those that may be propelled by the mechanical energy of grinding cutting etc Once the contaminant is captured the flow rate within the ducting must be sufficient to transport the contaminant to the filtering system and on to the exhaust In a system with many duct branches to individual hoods there may be a header system Whether simple or complex the ducting structure and dimensions will influence the air flow rate The flow rate must be sufficient to dilute flammable or combustible contaminants and not allow an accumulation within the ducting that could lead to a fire The design work or process needs or employee use can influence flow rates Over time wear and tear can cause the flow rates to reduce Regu
9. hazards A ico AA 8 Chapter 3 HEALTH AND SAFETY AUTHORITY A AA AUTHORITY A fan may be incorrectly placed so that a major section of the ducting is under positive pressure Where this ducting is within the workplace any leakage on the positive pressure side has the potential to expose employees who may or may not be involved in the process and may be unaware of their exposure Where ducting is wrongly sized the transport velocity within the duct may be insufficient and contaminant will settle out in the ducting This can be a serious fire hazard if combustible or flammable contaminants are being extracted Flammable vapours materials are being extracted but no consideration has been given to the prevention of a source of ignition or to dilution well below the lower explosion limit Poor design of exhaust point may cause the contaminants to be captured by the air supply system for example instead of being exhausted and diluted they may enter a downdraught caused by adjacent buildings and re enter the workplace HEALTH AND SAFETY Chapter 3 9 Elements of LEV system Most systems have the following five elements 1 An inlet enclosure hood where the contaminant is captured or contained and enters the LEV 2 Ducting This conducts air and the contaminant from the hood to the discharge point 3 Air cleaner or filter This filters or cleans the extracted air Not all systems need air cleaning 4 Air mover The fan
10. indicator at the hood to show the system is performing correctly Fume hood cupboard and biological safety cabinet standards reguire visible indicators These indicators can have numbers such as flow rate or negative pressure or colour coded bands for acceptable ranges See I S EN14175 1 to 7 FUME CUPBOARDS for detailed requirements A AA HEALTH AND SAFETY Chapter 3 AUTHORITY 15 2 Ducting The hood or inlet devices must be connected to a duct or ducting system depending on the complexity of the system which will effectively contain contaminants transported from the inlet and efficiently with proper flow control deliver the exhaust flow to the discharge a The ducting has to be sized and oriented so that the flow within it is efficient e g approaching laminar flow rather than turbulence The flow rates within the ducting should be sufficient to transport the contaminant to the outlet or filtering system Flow rates can vary greatly depending on the nature of the contaminant The rate should be sufficient to allow the contaminant be transported and not deposited on the walls of the ducting where it can reduce flow efficiency and become a possible fire or explosion hazard depending on the nature of the contaminant tet lobo el Wi a E N KY A TE KR KE a My a Small joining angle R not less than 11 2 times D Flanged joints TTT TT i dd a i ie ee EL fal Slip joint Achieving
11. use 1 organise thorough monitoring and performance testing at least every 14 months 2 document inspections and performance testing 3 prioritise remedial or overhauling maintenance where necessary Routine monitoring Routine checks keep the LEV system running properly Ideally the freguency of routine checks and their description should be set out and recorded in a log book An employee should be trained to make routine checks Failures detected should be reported and then acted upon Routine checks can include e checking manometer readings are in the correct range e checking static pressure readings e checking ducts and hoods not damaged e checking there is no visible leakage e checking filter system Annual performance testing An annual examination and performance monitoring should be a detailed systematic examination to ensure the LEV continues as intended by design to achieve adeguate control The testing and examination may be carried out by an employee who is competent in the operation of the LEV system or an outside contractor such as a consultant occupational hygienist or ventilation engineer A AA HEALTH AND SAFETY Chapter 12 51 AUTHORITY There are a variety of instruments such as different types of anemometers varieties of Pitot tubes and various manometers used to measure air velocity There is also the consideration of good technigue when using a measuring instrument The manufacturer of the L
12. which is relative to flow rate Air velocity to transport particles and prevent deposition within the duct which could be a fire or explosion hazard A AA HEALTH AND SAFETY AUTHORITY Turbulence Turbulent flow Vector Velocity pressure Volume flow rate Wake Working zone HEALTH AND SAFETY AUTHORITY Non laminar air flow A major contributor to reductions in velocities and hence deposition in the duct work Where the velocity varies rapidly at any point in an irregular manner The speed and direction of the contaminant cloud Pressure exerted by air relative to flow Measurement scale cubic metres per second m3 s some sources cubic feet per minute cfm A low pressure region that forms downstream of a body in an air flow The area where the contaminant cloud is being created and the volume of air affected Chapter 18 69 A country where worker safety health and welfar and the safe management of Chemicals are central to successful enterprise HEALTH AND SAFETY AUTHORITY Tel 1890 289 389 International Callers 00353 1 6147000 Fax 01 6147020 www hsa e HEALTH AND SAFETY ISBN NO 978 84496 92 4 AUTHORITY HSA04 6
13. Chapter 12 55 AUTHORITY Also consult EN 14175 1 to 7 FUME CUPBOARD standards relating to hoods See standards section below Once the system has been set up balanced and a base line established to demonstrate it can deliver design air flows the static pressures taken with the base line measurements can be used to determine the ongoing actual system performance if the system has in line static pressure gauges manometers The manometers can be easily read and logged as part of the routine testing and give a quick indication of the air flow performance level In general if the static pressure readings are 20 above or below the base line limits then remedial action needs to be taken When measuring performance there are a number of essential points e Monitoring should be carried out where conditions reflect the true working environment e Ensure that environmental conditions in the workplace doors windows draughts movement etc are not adversely affecting flow rates The measurement points should be well chosen to ensure an accurate reading e The employee or consultant carrying out the monitoring should have an understanding of the ventilation system the monitoring techniques the potential for errors and how to interpret results By proper monitoring and ongoing checking the employer can be assured that the LEV system is operating as designed and with regular non onerous checking static pressure readings any det
14. EV may give instructions on monitoring Because of these complexities it is important that the examiner auditor whether in house or an external contractor can demonstrate their competence in completing the performance monitoring Before carrying out any testing the work to be done should be assessed for risks and appropriate action taken The employee or contractor needs to know if there are any material residues within the system that could be hazardous Are there physical hazards such as working from heights electrical hazards moving machinery manual handling specific to the LEV testing Examining filters and scrubbers may increase the risk of chemical contact and the hazards associated with entering a confined space Before carrying out any measurements the examiner should have available to him or her e a copy of the commissioning report e the results of the previous annual performance testing if appropriate e thelog of routine testing He she should be able to confirm that there have been no modifications to the system since the last testing If these reports are not available then this test has to become the base line test His her report should recommend documented routine testing as outlined above Physical examination Before any flow measurement the examiner should carry out a thorough physical examination of the system and all its components looking for damage corrosion or wear and tear e Check around the hood enc
15. Manual of Recommended Practice for Design American Conference of Governmental Industrial Hygienists ACGIH ISBN 978 1 607260 13 4 INDUSTRIAL VENTILATION A Manual of Recommended Practice for Operation and Maintenance American Conference of Governmental Industrial Hygienists ACGIH ISBN 978 1 882417 66 7 A ee AA 62 Chapter 15 HEALTH AND SAFETY AUTHORITY Chapter 16 Building and Engineering Services Association UK Engineers Ireland Irish Ventilation Industry Association www ivia ie Maintenance examination and testing of local exhaust ventilation HSG 54 HSE UK A AA ne DE Chapter 16 63 Chapter 17 American National Standards Institute ANSI www ansi org American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE www ashrae org British Occupational Hygiene Society BOHS www bohs org Building and Engineering Services Association UK www b es org Building Services Research and Information Association UK www bsria co uk Chartered Institution of Building Services Engineers CIBSE www cibse org Engineers Ireland www engineersireland ie Irish Ventilation Industry Association IVIA www ivia ie National Standards Authority of Ireland www nsai ie Occupational Hygiene Society of Ireland OHSI www ohsi ie A ee AA 64 Chapter 17 HEALTH AND SAFETY AUTHORITY Chapter 18 Aerosol Air changes Air cleaner Air filter Air mover Blast gate Boun
16. agrams The initial performance from commissioning Checks maintenance and parts replacement schedules Signs of wear and control failure to monitor Description of how operators should use the LEV so it works effectively A list of replaceable parts Once the design specifications have been agreed the installation and commissioning phase can commence The complexity of the system will have a major impact on this phase The employer needs to consider how the work will impinge on his enterprise The first step is the project management construction and installation phase Will fabrication be carried out on site Is this a large installation affecting major parts of the premises For construction site requirements see the HSA website www hsa ie under Construction There are specific requirements laid down in the Safety Health and Welfare at Work Construction Regulations 2006 S I 504 of 2006 as amended Make sure the system is installed as agreed in initial specification A BA HEALTH AND SAFETY Chapter 9 43 AUTHORITY Once installed the commissioning phase begins Commissioning is proving the LEV system is 1 capable of providing adeguate control and 2 working to design The commissioning activity must consider the work practices as well as the LEV hardware if it is to be a true measure of performance Components of the commissioning process would be physically checking the integrity of the system e Is it fab
17. ams gt Instructions on how to use the LEV gt Performance information collected during commissioning gt Daily weekly and longer term checks gt Common early signs of deterioration in performance or wear and tear gt Details of what checks should be carried out at each annual examination and test of the system Checking and maintaining existing LEV The system needs to be thoroughly examined regularly to demonstrate it is performing to design It is recommended that the system be checked at least every 14 months or more frequently if the manufacturer recommends it Also simple routine checks can be carried out when the system is in use As well as checking exhaust performance rates checks and maintenance of the complete system are essential especially moving parts that wear e g fan motors drives gear wheels fan belts fan bearings filter shakers hoods ductwork flanges and seals that can be corroded or damaged also need to be checked along with any parts that may deteriorate with use e g filters flexible ducting and items that need regular attention e g dust collectors cyclones scrubbers System parts that are outdoors may in time become corroded and leak A record log book should be kept which indicates the initial design criteria and required monitoring checks actual records and dates of performance monitoring maintenance parts replacement or any modification to the system A BA HEALTH AND SAFETY Chapter 9
18. and motor that powers the extraction system 5 Discharge or exhaust This releases the extracted air to a safe place Contaminant N anmannan nnmnnn nanny A PPP een esel Ducting Air cleaner Exhaust Fan R 10 Chapter 3 HEALTH AND SAFETY AUTHORITY The unit in its entirety must be of good design For example A AA Leak proof leakage on the suction or negative pressure side of the air remover will lead to inefficient extraction and leakage on the positive pressure side and may reintroduce the contaminant to the workplace The flow rate of air through the system must be sufficient to achieve the initial capture containment and carry all contaminants to the purifying filtering system transport velocity Combustible dusts wood dust for example if not extracted properly can deposit in the ducting and be a fire or explosion risk Flammable solvents being captured by the system need to be diluted by sufficient air flow to prevent the formation of a flammable mixture The ducting needs to be structured so as to avoid eddy currents and inefficient flow For example it should not have sharp right angled turns as this leads to dead areas with no flow The construction and materials of construction need to be compatible with the contaminants being extracted For example where flammable gases or vapours are being extracted the system should not be able to generate a source of ignition Likely igniti
19. ar to year to demonstrate ongoing effectiveness of the system and to assist in determining any deterioration by way of comparison with previous results Any deficiencies found during system monitoring should be rectified to ensure the LEV is effective when in use and these interventions modifications should be included in LEV records Where maintenance work involves any entry into a confined space records of checks made prior to entry should be made Where the employer uses anemometers or similar equipment to monitor ventilation performance the calibration certificates certificates of conformance etc should be kept on file A AA HEALTH AND SAFETY Chapter 11 49 AUTHORITY ara Examining amp Mi This section gives guidance on the key points regarding examination and performance monitoring The examiner auditor engineer technician employee carrying out the testing needs to be competent and have a knowledge of LEV monitoring beyond the fundamental points outlined below The examining and monitoring of LEV is different from the normal use and should be risk assessed appropriately before commencing the examination It will for example be necessary to lock out or de energise systems such as fan motors during examination and there may be confined space hazards where filter housings must be entered The risk of contact with contaminant may also be a factor The LEV should be monitored by the user on an ongoing or routine basis when in
20. be reduced to approximately 10 of the total volume Therefore 1 good design to maximise performance and 2 proper positioning of flexible systems are crucial e A fume cupboard to take an example operates at a sash plane face velocity of 0 5 m s This flow can easily be overcome by counter currents and uncontrolled draughts This can be easily demonstrated with smoke testing In order to maintain its effectiveness it is important that the hood be used correctly For example work should be kept well into the hood the sash should be open to the minimum to allow work to proceed and the external environment should be controlled so that draughts or sudden changes in air supply do not challenge the fume cupboard performance This holds true for all LEV the hood booth should be used as designed and the external environment should be controlled to avoid challenging the flow rate e Remember air flow is seldom uniform or laminar Surfaces cause drag which can lead to low no flow or eddies e The operator s body or other solid objects if placed in the flow path will obstruct flow and generate dead areas See the illustrations below Example Heavier than air aerosol How Hexane air mixture really flows Is this how Hexane flows Is this how Hexane flows out of a mixer out of a mixer and is sucked away by the LEV slot Misconception A BA HEALTH AND SAFETY Chapter 5 31 AUTHORITY Air flow patterns How do peopl
21. creased potential for exposure and depending on the type and complexity of the filtering system it may be necessary to draw up procedures for safe entry to filter housing and for regular changing cleaning and maintenance of filters Air mover or fan The air mover needs to be suitable for use It will need to provide a sufficient air flow rate to efficiently extract the contaminant including a sufficient in duct velocity to transport the contaminant to the cleaning filtering system and prevent flammable material for example depositing within the ducting The air mover should be able to cope with increased pressure as the filtering element becomes loaded The air mover should not provide a source of ignition The air mover and its components should be impervious to corrosion abrasion damage by the contaminants Discharge system The discharge ducting should be placed so that it does not affect any air supply system The air being exhausted should not be entrained and recirculated into the workplace through the air supply system HEALTH AND SAFETY Chapter 3 17 AUTHORITY Local Exhaust Ventilation LEV Guidance Disadvantages of LEV e If the LEV is incorrectly placed contaminants can be drawn into a the operators breathing zone and b the process Emissions drawn into the system must be disposed of safely and without adverse effects on the environment e It is an additional system to operate and maintain oth
22. dary layer Breathing zone Canopy hood Capture velocity Capture zone Capturing hood HEALTH AND SAFETY AUTHORITY Small particles solid or liguid suspended in the air The diameter of the particles may vary from 100 um to 0 01 um e g dust fog smoke The number of air changes per hour a measure of dilution ventilation is calculated by dividing the extraction volume per hour by the enclosure or building volume e g 8 to 12 air changes per hour A device designed for the purpose of removing contaminants from the air Can include scrubbers filters and electrostatic precipitators An air cleaning device that removes particulate load from air stream Fan Sliding damper The stationary or turbulent layers of air near a surface which can hold a contaminant cloud The region around operators from which they draw air for breathing A receiving hood over a hot process The air velocity at any point in front of the hood or at the hood opening necessary to overcome opposing air currents and capture the contaminated air at that point by causing it to flow into the hood A three dimensional envelope in front of a capturing hood in which the capture velocity is adequate A capturing hood must generate sufficient air flow at and around the source to capture and draw the contaminant into it The source and the contaminant cloud are outside the hood Chapter 18 65 Clearance time Commissioning Cyclone Di
23. ds arising such as potential exposure to contaminants and the hazards of possible entry into a confined space The risk assessment should highlight possible risks that need action The employer should keep training records for each concerned employee Changes to the work process and LEV mean that staff may need retraining HEALTH AND SAFETY ee AUTHORITY Chapter 11 Keeping records as outlined below is crucial to demonstrate that the system is effective has been performing as designed and continues to do so On installation the employer should receive a user manual from the installer manufacturer which should be kept on record for future reference and training User manual contents gt Initial specification gt Design criteria gt Initial performance measurements gt Purpose and description of the LEV system including drawings and diagrams gt Instructions on how to use the LEV gt Performance information collected during commissioning gt Daily weekly and longer term checks gt Common early signs of deterioration in performance or wear and tear gt Details of what checks should be carried out at each annual examination and test of the system If no records are available e g a commissioning report a competent ventilation engineer or occupational hygienist can assist to determine the effectiveness of the system and what measures are needed for adequate control Maintenance records should be kept from ye
24. e think air Reducing size and protrusion flows into a booth of eddies Misconception Sprayer may believe hes Actual pattern of airflow ina Why does this airflow instantly protected typical downdraft booth pattern matter Misconception Reality H Oo Ya 32 Chapter 5 HEALTH AND SAFETY AUTHORITY HEALTH AND SAFETY AUTHORITY Case Study Sack emptying with LEV control Sack disposal with no LEV control Has control for sack emptying But no control for sack Chapter 5 733 Canopy hoods do not protect people directly involved in a process They do not protect operators working on the hot process and or handling hot warm product 34 Chapter 5 HEALTH AND SAFETY AUTHORITY Chapter 6 Air contaminants mix with the air to form aerosols The air can be contaminated with gases vapours mist dust fumes and fibres Examples of contaminants and their properties Name Example Gas Carbon monoxide Carbon dioxide Vapour Acetone ethanol chloroform styrene petrol Fibres Asbestos Glass Mist Solution being sprayed e g paint steam electroplating baths Fume Solder or welding fumes Dust Flour dust Concrete cement dust generated by grinding cutting crushing drilling etc Silica from stone cutting HEALTH AND SAFETY AUTHORITY Description Invisible gas at room temperature Normally a liquid at standard temperature and pressure Volatile and evapo
25. ed to an area where it cannot be entrained into the air supply system and re enter the building When designing and placing exhaust stacks there is often a desire for aesthetic or environmental reasons to keep the stack low lying and out of sight Exhaust from this type of system may not go beyond the building boundary layer and will re enter fresh air inlets When designing discharge points the buildings dimensions or features which can affect air flow e g solid roof enclosure must be taken into account The dimensions of adjacent buildings including their height can have negative air flow effects down flow channelling or relatively no flow and the prevailing winds should also be considered The discharge ducting must be designed to give sufficient exhaust plume velocity for clearance Rain ingress may occur and drain points will be necessary Location of discharge stack Recirculation possible poor design Low discharge stack relative to building height Air inlets on roof and wall A AA Chapter 4 HEALTH AND SAFETY AUTHORITY Chapter 5 Below are some of the commonly held misconceptions regarding LEV e Air being drawn into a ducting system is drawn from many directions unless directed or controlled by a hood As a conseguence as the source moves from the hood the air flow towards the hood diminishes rapidly As a rule of thumb for round ducting at one diameter distance from the opening the air flow will
26. ely for example how to correctly place an extraction hood e appreciate the limitations of the system and how they might render it ineffective Often employers employees overestimate the robustness of the LEV system and do not appreciate that the system can easily be rendered ineffective by environmental changes outside the design specifications for example changes in general ventilation draughts misuse or misplacement of equipment for example misuse of a fume cupboard or failure to maintain and monitor performance Capturing hood Velocity contours and airflow lines z O O a Rule of thumb E 10 face velocity 1d from face This simple rule of thumb is crucial in understanding the limitations of exhaust ventilation and where best to place the exhaust hood Operators frequently place mobile hoods too far from the emission point significantly reducing the systems effectiveness Hoods fixe d to ducting can control and focus flow direction to maximise performance 2 L s m s ae F O dd e e e a o d diameter YT 01934507080 A BA HEALTH AND SAFETY Chapter 10 47 AUTHORITY e know how to check that the LEV is working reading flow indicators pressure differential meters e know what actions to take in the event of a system failure Maintenance staff will need the above training and relevant specific training relating to the maintenance of the system and hazar
27. erioration in performance will be quickly detected should a fault arise For more comprehensive data on performance measuring techniques consult the publications in the reference section of these guidelines A o AL 56 Chapter 12 HEALTH AND SAFETY AUTHORITY Chapter 13 Not an exhaustive list Safety Health and Welfare at Work Act 2005 In essence the Act reguires the employer to manage health and safety in the workplace and to prevent and reduce risks to health and safety through the provision of safe systems of work by completing a risk assessment and putting controls in place He she is also reguired to consult with employees or their safety representative to provide adeguate instruction training supervision and any necessary information The Act also has duties for employees which include taking reasonable care to protect their safety and that of others affected by their acts or omissions attending appropriate training and instruction given by their employer correctly using any article substance protective clothing and eguipment provided for use at work by their employer to protect their safety or health to reporting to their supervisor or other appropriate person 1 work being carried out in a manner that may endanger health or safety 2 contraventions of the statutory provisions that may endanger health or safety or 3 defects in the workplace system or eguipment REGULATION EC No 1907 2006 Registration
28. erwise it could become an exposure and or fire hazard e Employees must be properly trained in the systems correct use its effectiveness and maintenance needs i HEALTH AND SAFETY ee _ AUTHORITY Chapter 4 An inlet enclosure hood where the contaminant is captured contained or enters the LEV There are many types of hoods depending on reguirements capturing hood small enclosure walk in booth down flow booth receiving hood partial enclosure total enclosure from small on tool extraction such as on a soldering iron to a walk in booth for spray painting Local exhaust ventilation hoods Local Hood Downdraft Hood Downdraft Hood Booth Hood Canopy Hood Enclosure Hood h HEALTH AND SAFETY Chapter 4 19 AUTHORITY LEV hood classification expanded _ Enclosures Full Partial large Partial small Room Receiving nm om aS a e e ant E a e gt De FAA D 20 Chapter 4 HEALTH AND SAFETY AUTHORITY Fixed capturing hood Moveable capturing hoods LVHV Low Volume High Velocity Welding frame Solder fume Small capturing hoods often built in Low Volume High Velocity LVHV HEALTH AND SAFETY h a pter Al 2 1 AUTHORITY Improved hood effectiveness and efficiency through enclosure 1600 cu ft min 0 755m sec of X j say ny Pi 3 ES 12 305 square opening R N nir a ity
29. extraction which uses very small hoods to capture contaminants very close to source using high velocity air extraction e g an extraction unit attached to a solder gun Chapter 18 67 Make up air Manometer Negative pressure Pitot tube Plenum Positive pressure Receiving hood Source Source strength Static pressure Total pressure Transport velocity Chapter 18 Air to replace extracted air If air supply is restricted the extraction will correspondingly reduce flow rate A pressure indicating device essentially a u tube filled with a suitable liquid so that the amount of liquid displacement indicates the pressure being exerted Air pressure lower than some reference point Device used to determine air flow performance by measuring total and Static pressure A device or structure to smooth air flows as in a walk in hood Air pressure higher than some reference point workplace A receiving hood receives and contains contaminant usually propelled by energy from the process also see capturing hood The process creates the source This is a creation of the contaminant cloud A combination of the volume rate of release of the contaminant cloud the cloud volume shape speed and contaminant concentration Air pressure measured normal to the flow direction The sum of the static and velocity pressure By measuring total and subtracting static pressure Pitot tube velocity pressure is estimated
30. gents as a result of their work The minimum containment measures are specified in Schedules 7 and 8 of the Regulations Safety Health and Welfare at Work Construction Regulations 2006 S I 504 of 2006 as amended The 2006 Regulations set out the main reguirements for the protection of the safety health and welfare of persons working on construction sites The Regulations apply to all construction projects including the alteration decoration maintenance and repair of buildings and the installation maintenance and removal of mechanical and other systems fixed within or to structures They place obligations on clients and designers to ensure that safety and health is taken into account before any construction work begins Contractors must ensure that the work on site is properly coordinated and carried out in a safe manner A AA Chapter 13 HEALTH AND SAFETY AUTHORITY Chapter 14 ANSI AIHA Z9 1 2006 Open Surface Tanks Ventilation and Operation ANSI AIHA Z9 2 2007 Fundamentals Governing the Design and Operation of Local Exhaust Systems ANSI AIHA Z9 3 2007 Spray Finishing Operations Safety Code for Design Construction and Ventilation ANSI AIHA Z9 4 2011 Abrasive Blasting Operations Ventilation and Safe Practices for Fixed Location Enclosures ANSI AIHA Z9 5 2011 Laboratory Ventilation ANSI AIHA Z9 6 2008 Exhaust Systems for Grinding Buffing and Polishing ANSI AIHA Z9 7 2007 Recirculation of Air from Industrial Pr
31. ginally designed A rr AL 36 Chapter 6 HEALTH AND SAFETY AUTHORITY Toxic or harmful The primary purpose of having LEV is to prevent employee exposure to hazardous chemical agents The contaminant may also be harmful to the environment and therefore filtering or scrubbing the discharge may be crucial Physical properties Where vapours are heavier than air it is important that the capturing containing devices are so placed that they are effective in exhausting the contaminant The contaminant may receive kinetic energy because of the process For example the evaporation rate of volatile solvents will increase with temperature Grinding cutting crushing drilling milling dropping materials through a hopper etc all provide energy which may propel the contaminant generate extensive aerosols and overwhelm LEV systems Particle size is important in that in general smaller particles can disperse further and remain airborne longer before settling on work surfaces Also the particle size determines whether or not a particle can be inhaled Particles with an aerodynamic diameter range of 0 01um up to 100um can be inhaled Within this range respirable particles lt 10 um can be inhaled deep into the alveolar region of the lungs Biological A biological safety cabinet is the common type of LEV for biological contaminants See the Health and Safety Authority s Guidelines for the Biological Agents Regulations for detailed guidance on
32. he specific needs of the employers processes must be provided commissioning process Performance indicator instruments such as manometers on hood ducts should be installed so that the employer and employees can determine and record if necessary the performance rate of the system The specification should indicate the training to be given to staff such as supervisors users and maintenance personnel at installation The employer should receive a user manual from the installer manufacturer for future reference and for training purposes see next chapter on installation and maintenance Employees must be consulted and involved in drawing up the specification to make sure the system to be installed is effective and practical for use The employer is responsible for making sure the supplier is competent to install the LEV system Compare their plans with the specification Check out their experience and competence to carry out the work A rr AA 42 Chapter 8 HEALTH AND SAFETY AUTHORITY Chapter 9 New LEV When installing LEV use a reputable supplier with experience of the type of control that is needed who can demonstrate that their system will adeguately control potential contaminants Installation and commissioning The LEV supplier should prepare a user manual describing what the LEV is designed to control and how it achieves control It should also contain the following e The LEV system description with drawings and di
33. itive diaphragm Glass U tube with liquid Alarms can fail without warning and need back up testing which should be detailed in the user manual Also faulty alarms can get muted because of the annoyance resulting in no alarm Depending on the complexity of the system the ducting may have ports for in line flow measurement by Pitot tube HEALTH AND SAFETY AUTHORITY Chapter 7 39 When the employer has completed a risk assessment evaluated the risks and determined the potential hazards from chemical agents control methods need to be considered As well as health hazards there may be flammability reactivity and physical excessive heat hazards In installing controls the employer having started at the top of the hierarchy has decided to install a local exhaust system to attain control The LEV system must be fit for purpose For example where the process entails grinding it is likely that dust will be propelled from the source and the system needs to be designed to contain or capture the fugitive dust Before designing or installing an LEV system a good understanding of contaminants and the process demands are necessary The following will also need to be considered Will the system be required to cope with changing materials and processes Does it need to be flexible adaptable simple or complex this depends on the processes and the potential exposure points the risk assessment has highlighted Are you an end user unde
34. laminar flow b It should be of sound and solid construction so that it does not allow inward or outward leakage and will not therefore be corroded by the contaminants being extracted or weather elements where ducting is external Leakage at joints or flanges results in the system not operating as designed It may lead to employee exposure or to uncontrolled release to the environment c Ideally all internal ducting in the workplace should be under negative pressure so that in the event of any leakage employees in the workplace are not exposed In the event of an outward leakage into the workplace employees could be inadvertently exposed and where ducting is extensive non involved employees in other areas may be unknowingly exposed A e AL 16 Chapter 3 HEALTH AND SAFETY AUTHORITY 3 A AA Air filtering collection or cleaning system The contamination removal filtering system should be fit for purpose The type of system used will be very much dictated by the type of contaminant being extracted and can vary from a simple filter system to a multi component system with pre filters and scrubbers for example Whatever the filtering system it should be designed so that it can cope with the contaminant load and remove filter it effectively without affecting flow performance It should be easily changed cleaned and maintained without causing exposure to operations or maintenance staff Following risk assessment because of the in
35. lar monitoring is crucial General capture velocities Dispersion Examples Air flow rate m s Little Evaporation from tanks degreasing 0 4 0 5 Average Intermittent container filling low speed conveyor 0 5 1 0 transfers welding plating High Barrel filling conveyor loading crushers 1 0 2 5 Very high Grinding abrasive blasting tumbling dumping 2 5 10 Influencing factors Strength of cross draughts from make up air traffic barriers etc Toxicity of contaminants volatility other exposures A AA 38 Chapter 7 HEALTH AND SAFETY AUTHORITY General duct velocities Type of contaminant Examples Duct velocity Dry dusts and powders 15 m s Average industrial dust Grinding dust wood shavings asbestos silica 20 m s clay brick cutting Heavy dusts Sawdust lead metal turnings damp materials 25 m s Instrumentation There are a number of types of instruments that may be used to measure air flow to determine the system performance the simplest being a ribbon type device that is moved by the air flow to indicate flow to the more complicated electronic device a pressure transducer which can activate alarms if the flow drops below a predetermined range Fume cupboards for example should have visual indicators with alarms as per EN 14175 2 FUME CUPBOARDS Safety and Performance Requirements Airflow indicator Manometer types Electronic pressure transducer Mechanical pressure sens
36. losure for soiling and deposits which would indicate that the contaminants are not being extracted properly the flow rate may not be effective filtering devices may be blocked for example There could be a number of causes see questions below for an accumulation of contaminants including poor or no testing servicing A o AL 52 Chapter 12 HEALTH AND SAFETY AUTHORITY e Are connections and flanges well sealed Is there staining to suggest outward leakage e Are inspection ports in place Is the system intact Check all sides of ducting for damage corrosion holes e Are hoods enclosures in good condition and working as designed doors sealing baffles and fume cupboard sashes movable etc e Are manometers easily read and indicating correctly e Are orifice blast gates in place and secure e Is the flow through hoods or booths impeded by storage of materials within them A hood is not a storage cabinet and it is important that only items being used for work are placed with in it Over filling will lead to undesirable turbulence and dead spots e Are filtering systems to be overhauled Are they intact This may involve opening the system and changing filters bags etc leading to potential exposure to contaminant Are wet scrubbers in use Again these will need specific monitoring to determine the scrubbing of exhaust air is effective Any filter scrubber system may involve access to confined spaces for both ducting and fil
37. lution ventilation Displacement ventilation Duct velocity Dust collector Dust lamp Eddy Electrostatic precipitator Enclosing hood 66 Chapter 18 The time taken for a contaminant to clear from a room or enclosure once generation has stopped Initial appraisal of intended operating performance Proof that an LEV system is capable of providing adequate control An air cleaning device to remove particles from air by centrifugal force A controlled supply of clean air into the work place mixing with contaminated air and reducing exposure concentrations The air may also be exhausted through a separate exhaust system which can be high and low point exhaust to remove lighter and heavier than air contaminants respectively Clean air displaces the contaminated air with minimal mixing Rarely effective due to eddies The average air velocity measured on a duct cross section An air cleaning device to remove heavy particulate from exhaust systems A Tyndall lamp or beam A parallel light beam illuminates the dust cloud to produce forwards scattering of the light enabling the assessment of particle cloud size and movement A region in air flow with a rotary motion contrary to the main flow which is common with obstructions and high air flows A type of particle filter Charged particles are attracted to a plate of opposite polarity to which they attach A full enclosure contains the process A room enclosure con
38. ng can demonstrate qualitatively the performance for booths fume cupboards receiving or capturing hoods The test can highlight eddies and turbulence which can significantly affect performance e A Tyndall lamp can also be used to demonstrate containment and capture of dusts and fumes The use of smoke testing and the Tyndall lamp can be very effective in visualising flow direction velocity contours eddy current etc Monitoring for air flowing through a duct is not uniform across the duct at any given cross section Frictional drag along the ducts causes the air near the surface of the duct to flow slower than the air in the centre of the duct Duct fittings and obstacles such as elbows branches contractions dampers cause significant variation in the velocity profile Under ideal conditions the velocity will increase with distance from the inner surface to the centre of the duct so taking a centre point reading alone will over estimate the flow rate To accurately estimate the average velocity measurements must be taken at representative points across the entire cross section of the duct This can be done by inserting a Pitot tube into a hole in the duct and taking readings at different depths along the diameter or traverse For sampling locations to be representative every area of the duct should have an equal chance of being sampled For this reason the traverse points are not evenly spaced but instead are chosen so that each poin
39. nterface with the system is vital The LEV system must be fit for purpose For example where the process entails grinding it is likely that dust will be propelled from the source and the system needs to be designed to contain and capture the fugitive dust Before designing or installing an LEV system a good understanding of contaminants and