where C air is the air concentration (mg/m 3 ); B the breathing rate (m3/h); t the exposure time (h). Further information Cherrie J, Howie R, Semple S (2010). Dermal and ingestion exposure meas urement In: Monitoring for health hazards at work , 4th edn. Wiley-Blackwell, Oxford. 30_Smedley_Chap30.indd 621 1/2/2013 12:51:26 PM This page intentionally left blank 623 Chapter 31 Biological monitoring Biological monitoring and biological effect monitoring 624 Interpretation of data 626 Pract ical and ethical considerations 630 31_Smedley_Chap31.indd 623 1/2/2013 12:52:50 PM CHAPTER 31 Biological monitoring 624 Biological monitoring and biological effect monitoring De \201 nitions Biological monitori ng The measurement and assessment of hazardous substances or their metabolites in tissue, s ecretions, excreta, expired air, or any combina- tion of these in exposed workers. Examples of blood and urine biological monitoring (BM) are shown in Table 31.1. Biological effect monitoring The measurement and assessment of a biological effect (early c onse- quences of exposure) in exposed workers, caused by absorption of chemicals. BM provides an indication of a workplace agent causing some detect- able biochemical altera tion. Unlike BM, biological effect monitoring BEM is not a surrogate of absorbed dose, but provides evidence of exposure. Examples of BEM include measuring the following biochemical responses: \200 Cholinesterase activity following an acute exposure to organophosphorus pesticides Urinary 2 -microglobulin proteins following exposure to cadmium \200 Free erythrocyte protoporphyrin (FEP) in blood or -aminolaevulinic acid (ALA-D) in urine for workers exposed to inorganic lead. Biological monitoring \200 Unlike air monitoring (external exposure) BM integrates exposu re received from all routes BM can be a useful complementary technique to air monitoring, particularly when exposure vi a the dermal route is signi \201 cant. Examples of chemicals which have the potential to p enetrate skin include those assigned the \200\230Sk \200\231 notation BM data can give useful information on the effectiveness of industrial hygiene controls, e. g. personal respiratory protective equipment as well as individual work practice BM sampling methods may be invasive and it may be dif \201 cult to distinguish between exposure at and away from work. 31_Smedley_Chap31.indd 624 1/2/2013 12:52:50 PM BIOLOGICAL MONITORING AND BIOLOGICAL EFFECT MONITORING 625 Table 31.1 Biological (blood and urine) samples and analytes Biological sample Example of parent compound Examples of metabolite Aromatic compounds: p henylmercapturic acid (for benzene), hippuric acid (for toluene), met hyl hippuric acids (for xylene), mandelic acid (for styrene and ethyl benzene), 1-hydroxypy rene (for PAHs) Urine Metals: mercury, lead (organic), cadmium, chromium, cobalt, vanadium Organic solvents: meth yl ethyl ketone (MEK), acetone, phenol, pentachlorophenol, 4,4 \200\231-methylene bis-2-cho roaniline (MbOCA) Chlorinated solvents: t richloroacetic acid (for trichloroethylene, perchloroethylene, 1,1, 1, trichloroethane) Other organic compounds: e .g. dialkylphosphates (for organophosphorous pesticides), 2,5-he xanedione (for n -hexane) Blood Metals: inorganic lead, mercury, cadmium, cobalt Organic solvents: aromatic compounds, e.g. toluene, styrene Chlorinated solvents: trichloroethylene, tetrachloroethylene, 1,1,1 trich loroethylene, Inorganic gasses and chlorinated solvents: c arboxyhaemoglobin (for methylene chloride and carbon monoxide), trichloroethanol (for trichloroethylene) 31_Smedley_Chap31.indd 625 1/2/2013 12:52:50 PM CHAPTER 31 Biological monitoring 626 Interpretation of data Units and creatinine correction \200 Blood samples: in micrograms ( g) or milligrams per liter (mg/L). \200 Urine levels: in milligrams per gram (mg/g) of creatinine, or millimoles per millimole (mmol/mmol) of creatinine. Urine concentration c an vary widely because of variation in \202 uid intake and sweat. Concentration/ dilution effects are corrected by adjusting for speci \201 c gravity or creatinine correction. Cre atinine correction is not advised if the creatinine <3 or >30mmol/L. Biological exposure limits BM data are usually compared with biological exposure standards set by national authorities. Examples include the following: \200 The TLV list of the ACGIH contains Biological Exposure Indices (BEIs ). 1 The BEI are advisory referen ce values and represent the concentration of a substance that is likely to be found in the sample of a worker who was exposed through inhalation to the TLV . The Deutsche Forschungsgemeinschaft (DFG, the German Research Foundation) publishes an annu al list of biological tolerance values (BAT). A BAT is de \201 ned as a maximum permissibl e quantity of a substance which does not generally impair the health of a worker. Thus the BAT value is primarily health based. In the UK there is a statutory requirement for monitoring lead under the CLAW Regulations. Under CLAW, action and suspension levels are assigned for lead workers. However, for other substances hazardous to health the HSE has adopted non-statutor y biological monitoring guidance values (BMGVs). Biological monitoring guidance values \200 BMGVs are non-statutory. Where the BMGVs are e xceeded, this indicates that work practices and controls need to be investigated. It does n ot imply that health effects will occur or that the WEL is exceeded. Table 31.2 gives a lis t of chemicals and their assigned BMGV values. For each substance, a free lea \202 et is a vailable from the HSE describing the analytical method, sampling strategy, quality assuranc e schemes, and interpretation of results BMGVs for different substances may be based on different information types which may include one of the following: \200 relationship between biological concen trations and health effects \200 relationship between biological concentrations and expos ure at the level of the workplace exposure limit (WEL) or data collected from representative samples of workplaces that are using principles of good occupational hygiene practice to minimize exposure. 1 ACGIH (2011). Threshold Limit Values for Chemical Substances and Physical agents & Biolog ical Exposure Indices . ACGIH, Cincinnati. 31_Smedley_Chap31.indd 626 1/2/2013 12:52:50 PM INTERPRETATION OF DATA 627 Table 31.2 BMGV values Substance BMGV Sampling time Butan-2-one 70 mol butan-2-one/Lin urine Post-shift 2-Butoxyethanol 240mmol butoxyacetic acid/ mol creatinine in urine Post-shift Carbon monoxide 30ppm carbon monoxide in end-tidal breath Post-shift Chromium VI 10 mol chromium/mol creatinine in urine Post-shift Cyclohexanone 2mmol cyclohexanol/mol creatinine in urine Post-shift Dichloromethane 30ppm carbon monoxide in end-tidal breath Post-shift N , N -dimetylacetamide 100mmol N -methylacetamide/ Post-shift mol creatinine in urine Glycerol trinitrate 15 mol total nitroglycols/mol creatinine in urine At the end of the period of exposure Lindane 35nmol/L (10 g/L) of lindane in whole blood (equivalent to 70nmol/L of lindane in plasma) Random MbOCA 15 mol total MbOCA/mol creatinine in urine Post-shift Mercury 20 mol/mol creatinine in urine Random 4-Methylpentan-2- one 20 mol 4-methyl pentan-2- one/L in urine Post-shift 4,4 -Methylene dianiline (MDA) 50 mol total MDA/mol creatinine in urine Post-shift for inhalation and pre-shift next day for dermal exposure Polyaromatic hydrocarbons (PAHs) 4 mol 1-hydroxypyrene/mol creatinine in urine Post-shift Xylene, o-, m -, p -, or mixed isomers 650mmol methyl hippuric acid/mol creatinine in urine Post-shift Crown copyright, material is reproduced with the permission of the Controller of HMSO an d Queen \200\231s Printer for Scotland. 31_Smedley_Chap31.indd 627 1/2/2013 12:52:50 PM CHAPTER 31 Biological monitoring 628 Interfering factors The following factors can affect BM results: \200 Diet ( \201 sh inc reases arsenic/mercury level) \200 Sex (females have higher erythrocyte protoporphyrin le vels than males) \200 Age (cadmium levels increase with age amongst smokers) \200 Alcoh ol intake affects the metabolism of organic solvents, e.g. styrene \200 Ethnic groups: ev idence for difference in metabolism of solvents \200 A metabolite of interest may be prod uced by more than one substance. Further information HSE (2007). Workplace exposure limits 2005 (amendments 2007), EH40/2005 . HSE Books, Sudbury. 31_Smedley_Chap31.indd 628 1/2/2013 12:52:50 PM This page intentionally left blank CHAPTER 31 Biological monitoring 630 Practical and ethical considerations Practicalities Several practical considerations must b e taken in to account before start- ing a BM program: \200 The reason for collecting samp les: compliance, risk assessment, health surveillance, epidemiological studies Appointment of a competent person to oversee the development and implementation of the program Criteria for selecting individuals for monitoring \200 Provision of information for subje cts, and obtaining individual consent. \200 Development of a suitable biological monitori ng strategy: timing of sample collection in relation to the beginning and end of shift or working week (see Table 31.3) number of samples to be taken \200 type of biological sample to be collected \200 subst ance or metabolite to be measured \200 amount of sample required Selection of suitable laboratory: experience of speci \201 c analysis, quality assurance schemes, validated analysis method Any special precautions for the collection, storage, stability, packaging, and dispatch of samples to a laboratory How the data will be interpreted, including non-occupational exposure. Feedback of grouped anonymized results to the workforce \200 Storage of data, and who has access to the data \200 Use of the data and likely bene \201 ts to the employees. Ethical considerations and access to data \200 Since BM involves taking samples from indi viduals it is essential that the rights of individuals are safeguarded The need for the monitoring, collection of samples, associated risks, and the use of data should be discussed and agreed with all concerned, employees, employers and workers representatives Workers must be made aware of what will be analyzed in the sample taken and what action may follows based on the results Results must be treated as con \201 dential and disclosed only to those health professiona ls the worker has agreed should have the results \200 The individual tested is entitled t o his/her results together with an explanation of them Group data can be provided to management and unions ensuring that any speci \201 c identi \201 ers are removed Under the UK COSHH Regulations, the results should be kept for at least 40 years from the date of last entry When companies cease operation they are advised to offer the data (both biological and personal inhalation) to the HSE. 31_Smedley_Chap31.indd 630 1/2/2013 12:52:50 PM PRACTICAL AND ETHICAL CONSIDERATIONS 631 Table 31.3 Half-life of chemicals and optimum sampling time: general relationship as a guid e for monitoring Half-life (h) Optimum sampling time <2 7 2 \200\22310 End of exposure End of exposure at the end of week shift or beginning of the next shift 7 10 \200\223100 End of exposure at the end of the working week >100 Random (sampling time not critical) Further information HSE (1997). Biological monitoring in the workplace , HSG 167. HSE Books , Sudbury. 31_Smedley_Chap31.indd 631 1/2/2013 12:52:50 PM This page intentionally left blank 633 Chapter 32 Prevention and control of exposure Exposure prevention and control 634 Control hierarchy: source, transmission, and individual 636 Software/organizational solutions 638 Hardware/engineering solutions 640 General (dilu tion) ventilation 642 Factors affecting performance of ventilation systems 643 Local exhaus t ventilation: assessing performance 646 Recording the examination and testing of local exh aust ventilation plant 648 Personal protective equipment: legal requirements, and use 650 Selecting respiratory equipm ent 652 Types of respiratory protective equipment 654 Hearing protectors 658 Predicting noi se reduction 660 Gloves 662 Protective clothing 664 Eye and face protection 666 32_Smedley_Chap32.indd 633 1/2/2013 12:54:27 PM CHAPTER 32 Prevention and control of exposure 634 Exposure prevention and control Prevention and control As far as exposure to hazardous subs tances is concerned, there is a legal duty under the COSHH Regulations to prevent or, where this is not rea- sonably practicable, to control exposure adequately. \200 Where it is n ot reasonably practicable to prevent exposure, the employer must apply protection measures appropriate to the activity including, in order of priority: \200 design and use of appropriate work processes, systems of work, engineering controls, and the provision of suitable work equipment and materials the control of exposure at source including use of ventilation systems and appropriate organizational measures to minimize the risks where adequate control of exposure cannot be achieved then suitable PPE should be used in addition to measures listed here. The measures used to control exposure should include: arrangements for safe handling, storage, transportation and disposal (waste materials) of substances hazardous to health suitable maintenance procedures \200 reducing the number of employees exposed, the level and duration of exposure, and the quantity of material used general ventilation \200 appropriate hygiene measures including adequate washing faciliti es. Exposure to carcinogens Where exposure to carcinogens cannot be prevented, the following co n- trol measures are required in addition to those described here. \200 Total enclosure o f process and handling systems \200 Prohibition of eating, drinking, and smoking \200 C leaning \202 oors, walls, and other surfaces at regular intervals \200 Designating thos e areas and equipment which may be contaminated \200 Storing, handling, and disposing of carcinogens safely, including use of closed and clearly labeled containers. Personal protective equipment \200 PPE provided by the employer should be suitable for th e purpose and comply with the Personal Protective Equipment Regulations 2002 \200 PPE inc luding protective clothing should be properly stored in a well-de \201 ned area, checked a t suitable intervals, and, if defective, repaired or replaced. Use of controls \200 Every employer who provides control measures is required to take reasonable steps to ensure that they are properly used Employees must make full and proper use of any control measures provided and report defects to their employer. 32_Smedley_Chap32.indd 634 1/2/2013 12:54:28 PM EXPOSURE PREVENTION AND CONTROL 635 Maintenance, examination, and testing of controls \200 Employers are required to maintain plant, equipment, engineering controls, and PPE in an ef \201 cient state, in ef \201 cient working order, and in clean condition All control measures including systems of work and supervision should be reviewed All LEV should be examined and tested every 14mths unless another interval is speci \201 e d, e.g. in Schedule 4 of the COSHH Regulations \200 Where RPE (other than disposable RPE) is used to control exposure the employer should ensure that it is examined and, where appropriate, tested at suitable i ntervals. Principles of good practice In the UK a set of principles of good control practice are used as a basis for judging whether control is adequate for hazardous substances. These include : \200 Design and operate processes and activities to minimize emission and the spread of agents Take in to account all relevant routes of exposure when developing control measures Control exposure by means that are proportional to health risk \200 Choose the most effec tive and reliable control options that minimize the emission and spread of health hazards Where adequate control cannot be achieved by other means, provide suitable PPE, in combination with other control measures Check and review regularly all aspects of control measures for their continuing effectiveness Inform and train employees about the hazards and risks from the agents with which they work and the use of control measures developed to minimize risks Ensure that the introduction of any control measures does not increase the overall risk to health and safety. 32_Smedley_Chap32.indd 635 1/2/2013 12:54:28 PM CHAPTER 32 Prevention and control of exposure 636 Control hierarchy: source, transmission, and the individual When controlling exposure to po llutants, the objective is to ensure that safe levels are achieved. The following three com ponents should be con- sidered in turn: (1) control at source; (2) prevent or control trans mission of the pollutant to the individual; (3) protect the worker. (1) Control at source \200 Eliminate the hazard by: changing the process or method of work so that the hazard is not created substitute hazardous with non-hazardous substances Modify the process to reduce the frequency, intensity or duration of emission Substitute substance with one of lower toxicity or different form of the same substance Enclose the process/sources of emission \200 Provide extraction ventilation \200 Improv e process/equipment maintenance \200 Limit areas of contamination, e.g. spills, leaks. Hierarchy of control: examples for noise and vibration \200 Use alternative tools (altere d frequency and amplitude) \200 Introduce or increase damping; isolate machine from \202 oor (noise) \200 Avoid/cushion impact. (2) Prevent/control transmission \200 Shielding between the worker and source \200 Incr ease distance \200 Housekeeping \200 Suf \201 cient dilution ventilation. Hierarchy of control: examples for noise and vibration \200 Re \202 ective and absorbent barriers \200 Active noise control. (3) Individual \200 Automatic or remote control \200 Enclose the worker \200 Safer wo rk practice and systems of work \200 Education, training, supervision 32_Smedley_Chap32.indd 636 1/2/2013 12:54:28 PM CONTROL HIERARCHY 637 Provide PPE \200 Reduce exposure time \200 Reduce number of workers exposed \200 Heal th surveillance. 32_Smedley_Chap32.indd 637 1/2/2013 12:54:28 PM CHAPTER 32 Prevention and control of exposure 638 Software/organizational solutions Options for controlling exposure to hazards in the workpl ace can be categorized broadly as software (management solutions) and hardware (engineering ) methods. Selection and use of PPE is discussed on b pp. 652 \200\22366. Hierarchy of software/organizational solutions Elimination Complete elimination of processe s or substances is usually dif \201 cult. Elimination is usually limited to unnecessary op erations or poor work practices. In some cases high-risk activities are subcontracted to an other operator. Substitution \200 By a less toxic substance: e.g. in painting using water-based solvents or organic solvents of lower vapor pressure By the same substance: but in a form that reduces exposure, e.g. use material in pellet form rather than as a powder. Designing or redesigning the process Reductions in exposure may be achieved by adjustments to the way the job is performed or modifying the layout of the process and the opera- tor \200\231s work procedures. For example, Fig. 32.1 shows alternative methods for drum \201 lling. Suppression of the substance Suppression can be achieved in a number of ways. For example, water is used as dust suppressant. Evaporation of vapor from volatile solvents in tanks can be suppressed by using a refrigerated strip just above the surface, creating a cool layer of concentrated vapor and reducing further evaporation. In electroplating the surfaces of t anks can be covered by \202 oating plastic spheres, which reduce the surface area availab le for evapo- ration, or by adding low-density liquid surfactants. Other software methods \200 Good work practice and systems (including good housekeeping) \200 Appropriate supervision \200 Job rotation \200 Information, instruction, and tra ining: the worker must be made aware of the following: \200 hazards to which they are exposed, and the risks to health \200 fac tors (process, equipment, method of work, environment) which may affect their exposure any relevant occupational exposure limits \200 signi \201 cant \201 ndings of risk ass essments \200 appropriate precautions and actions to be taken in order to safeguard health the correct use of control measures provided and how to recognize and report defects, e.g. PPE, engineering controls the signs and symptoms associated with the hazards and reporting requirements. 32_Smedley_Chap32.indd 638 1/2/2013 12:54:28 PM SOFTWARE/ORGANIZATIONAL SOLUTIONS 639 Vent pipe Vent pipe Storage vessel Storage vessel Normal filler Submerged filler Vented filler Bottom filling top venting Fig. 32.1 Alternative methods of drum \201 lling. (Reproduced from Sadhra SS, Rampal KG ( 1999). Occupational health - risk assessment and management.) With persmission from Wiley-B lackwell, Oxford. 32_Smedley_Chap32.indd 639 1/2/2013 12:54:28 PM CHAPTER 32 Prevention and control of exposure 640 Hardware/engineering solutions Engineering controls are often not well designed or well mai ntained and rely on the operator to use them correctly. The hierarchy of control is: \200 Total enclosure under negative pressure \200 Partial enclosure with extraction \200 Ge neral dilution ventilation (see b p. 642). Total enclosure under negative pressure To reduce exposure to very toxic substances the con taminants are han- dled in an enclosure under negative pressure, e.g. hot cells for radio-a ctive materials, glove boxes, and bead blasting cabinets. Partial enclosure with extraction Extraction booths The source of emission is enclosed on a ll sides, except where access is needed (Fig. 32.2(a)). Examples include chemical fume cupb oards and paint spray booths. Air velocity at the opening (face velocity) should be suf \201 cient to prevent escape of substance in to the environment. Typical face velocities fo r booths are in the range 0.5 \200\2232.5m/s. Canopies Canopies (Fig. 32.2(b)) are designed to draw upwards, and thus are best designed t o capture pollutants from hot processes, but are unsuitable if the worker needs to lean ove r the process. Hoods Hoods are placed at the side or behind the source in relation to the worker (Fig. 32. 2(c)). Typical capture velocities for pollutants range from 0.25 to 10m/s. \200 For hoods , the velocity decays rapidly with distance from the hood, e.g. for a circular hood the vel ocity is only approximately 10% of the face velocity one diameter away. For this reason, th e process should be conducted close to the hood, i.e. within the capture distance \200 On ce captured, pollutants need to be kept airborne in the ducting, which is achieved by minim um transportation velocities. Transportation velocities range from 7 to 10m/s for fumes to >20m/s for heavy and moist dust, e.g. paint-spraying particles Hoods with width to length ratios <0.2 are called slots. Slots are commonly used on degreasing tanks, cleaning baths, and electroplating tanks to remove vapor s and mists released from the tank surfaces. High velocity, low volume (HVLV) 1 HVLV extraction is used to draw particles directly from the point of release by a nozzle handling high air velocities. The chosen velocity must be higher than the tip speed of the tool, e.g. cutting, grinding, sanding. 1 De \201 nitions of velocities (face, capture, transportation) are given on page 676 32_Smedley_Chap32.indd 640 1/2/2013 12:54:28 PM HARDWARE/ENGINEERING SOLUTIONS 641 (a) (b) (c) Fig. 32.2 Extraction ventilation devices: (a) extraction booths. (b) Canopy hoods. (c) Open -face hood. 32_Smedley_Chap32.indd 641 1/2/2013 12:54:28 PM CHAPTER 32 Prevention and control of exposure 642 General (dilution) ventilation General (or dilution) ventilation reduces the concentration of the con- taminant by mixing the contaminated air with clean, uncontaminated air. Air is supplied to and from an area or building via air exhaust fans placed in the walls or roof o f a room or building. The air supply may also be \201 ltered and heated. General ventilation requirements are covered in the Workplace (Health, Safety and Welfare) Regulations 1992: \200 Fresh air is required to provide oxygen, remov e carbon dioxide, remove excess heat or, if conditioned, provide heat, remove odors, and dilute contaminants arising from workplace activities Air introduced into workplaces should be free of contaminants such as engine exhaust emissi ons or discharges from nearby extract outlets Air may be re-circulated to conserve energy costs. Re-circulated air, including air conditioning systems, should be \201 ltered to remove impurities and h ave fresh air added to it before being reintroduced to the workplace Mechanical ventilation systems should be regularly cleaned and tested to ensure that they a re kept clean from anything that may contaminate the air Insuf \201 cient air changes may lead to tiredness, lethargy, dry or itchy skin, and eye irritation CIBSE produces recommended fresh air supply rates per person (CIBSE Guide A: Environmental Design). The fresh air supply rate should not normally fall below 5 \200\2238L/s/occupant HSE has published detailed guidance on measures to avoid Legionnaires \200\231 disease caused by Legionella pneumophila which grows in water-cooling towers. 1 Use of general ventilation to control exposure to hazardous substances General ventilation is used to complement LEV systems in industrial envi- ronments. Occasionally, when the inst allation of LEV is impractical, e.g. in con \201 ned space, exposure reduction may be achi eved by dilution ventila- tion. The aim is to dilute a pollutant to a safe level before it reaches the breathing zone of the worker. When used to control chemical pollutants, dilution ventilation is limited to situations where the pollutants; \200 Are produced (released) at a low concentration a nd uniform rate \200 Are of relatively low toxicity \200 Not drawn or blown towards the worker(s). When designing dilution ventilation systems consideration needs to be given to the location of air inlet, position of source of the pollutant and the position of the work er. Dilution ventilation is more effective if the exhaust fan is located close to exposed w orker and the air supply (makeup air) is located behind the worker so that contaminated air is drawn away from the worker \200\231s breathing zone (Fig 32.3). 1 HSC (2000). Legionnaires \200\231 Disease. The control of legionella Bacteria in Water Sy stems. Approved Code of Practice and Guidance . HSE Books, Sudbury. ISBN 0717617726. 32_Smedley_Chap32.indd 642 1/2/2013 12:54:29 PM GENERAL (DILUTION) VENTILATION 643 (a) (b) Fig. 32.3 Example of good (a) and poor dilution (b) ventilation design. 32_Smedley_Chap32.indd 643 1/2/2013 12:54:29 PM CHAPTER 32 Prevention and control of exposure 644 Factors affecting performance of ventilation systems LEV systems comprise a hood, enclosure , or slot (negatively pressurized to ensure an inward current of air) connected to a fan vi a ducting with an air-cleaning device to ensure that the discharged air is \201 t for rec irculation or emission. Fig.32.4 shows components of an LEV system. Factors leading to poor performance LEV performance depends on its design, the integrity of its components and its maintenance and use. Inadequate performance results from: \200 In suf \201 cient enclosure \200 Low capture velocity \200 Extracted air volume is lower than the volume of pollutant released \200 Filters and air cleaners blocked \200 Restri cted, blocked, or damaged ducting \200 Ducting too resistant \200 Fan of the wrong type or size \200 Fan entry conditions unsatisfactory: bend or damper close to fan inlet affecting velocity pro \201 le Fans badly installed: the wrong way round or rotating in the wrong direction Fan blades dirty or corroded, or motor seized \200 Air discharge to atmosphere affected b y wind: best to discharge vertically. Weather shields must not restrict the air \202 ow from the discharge point No provision to allow make-up air to replace that extracted \200 Multi-branched system no t balanced \200 Poor maintenance and care \200 New workstation added without adjusting fan performance. LEV system components \200 Inlets : such as booths, hood, slot, canopy, or enclosure \200 Ducting: which may contain bends, junctions, dampers; it may be circular or rectangul ar in cross section and rigid or \202 exible Fans: usually centrifugal type \200 Air cleaners: such as bag \201 lter, wet scrubber, cyclone, or solvent recovery device Discharge: to atmosphere via a stack, diffuser, grille, or just open duct. 32_Smedley_Chap32.indd 644 1/2/2013 12:54:29 PM FACTORS AFFECTING PERFORMANCE OF VENTILATION SYSTEMS 645 Discharge Rectangular duct Diffuser Contraction Fan Junction Expander Air cleaner/ dust collector Bend Branch Circular ducts Booth Hood Fig. 32.4 Components of LEV system. HSE (1998). Maintenance, examination and testing of local exhaust ventilation , HSG54, \201 gure 1, p. 2. HSE Books, Sudbury. 32_Smedley_Chap32.indd 645 1/2/2013 12:54:29 PM CHAPTER 32 Prevention and control of exposure 646 Local exhaust ventilation: assessing performance Examination and testing According to HSG25 8 (2011) examination and testing of LEV involves three stages: \200 A through visual exam ination to verify the LEV is in ef \201 cient working order, in good repair, and in a clean condition Measurement and examination of the technical performance of the system against its speci \201 cation, i.e. comparison with original commissioning report Assessment to check the control of worker exposure is adequate. Visual and structural examination \200 External examination of all parts of the systems f or damage, wear and tear Check \201 lter cleaning devices (e.g. mechanical shake down system) are working correctly Check pressure (built in) gauges, e.g. located before and after \201 lter \200 Check th at the monitors and alert/alarms are working correctly \200 Check for deposits of settled dust in and around the LEV hood. Assessment of the technical performance \200 Static pre ssure measurements taken behind each hood, and across the \201 lter and the fan Check velocities (capture, face and transportation) of air at various points in the systems (as speci \201 ed in the system commissioning manual) Calculate the air \202 ow rates ( q ) at the face of the hood or booth and in the duct including at the \201 lter and fan: Q = v \227 a , where v is the velocity (m/s), a is the cross-section area of hood or duct (m 2 ) \200 Ch eck speed of fan and motor \200 Check the replacement or make-up air supply \200 Test t he air cleaner performance and any air re-circulating systems.- Compare the result of testi ng with the design speci \201 cation for the system. The assessment of control effectiveness \200 Ensure operator \200\231s working zone is wi thin capture zone of the LEV (Fig. 32.5) Dust lamp tests to check escape of \201 ne dust or mists \200 Smoke tube or leak tests \200 Observe the operator and work practice \200 Conduct air sampling to determine whet her control is achieved. 32_Smedley_Chap32.indd 646 1/2/2013 12:54:29 PM LOCAL EXHAUST VENTILATION: ASSESSING PERFORMANCE 647 Capture Zone Working Zone Fig. 32.5 Capture and working zone. Note: The capture zone is the space in front of the hoo d where the air velocity is suf \201 cient to capture the contaminant. The working zone is de \201 ned as the space where the activity generates the contaminant. For effective cont rol, the working zone must be lie within the capture zone of the hood. De \201 nitions \200 Capture velocity : the air velocity required at the source of emiss ion suf \201 cient to cause the pollutant to move towards the mouth of the extractor and t hus be successfully captured Face velocity : the air velocity at the opening of a hood or enclosure \200 Transportatio n velocity : minimum velocity required in the system, including ductwork and extract devices, to keep collected particles airborne and to prevent them from being deposited in the system Static pressure : the pressure exerted by a \202 uid in motion at right angles to the direction of \202 ow Velocity pressure : the pressure equivalent of the kinetic energy of a \202 uid in motion . It is calculated from the expression P v = 0.5 pv 2 where p is the density of air (kg/m 3 ) and v is the velocity of air (m/s). Total pressure : the sum of the static and velocity pressures at a point in an air stream. It can be +ve or \200\223ve relative to atmospheric pressure. Further information and guidance HSE (2011). Controlling airborne contaminants at work \200 \224a guide to local exhaust ventilation (LEV) , HSG258. HSE, Sudbury. Available at: M http://www.hse.gov.uk/pubns/priced/hsg258.pdf HSE (2008). Clearing the air \200\224a simple guide to buying and using local exhaust venti lation (LEV) , INDG408. HSE, Sudbury. Available at: M http://www.hse.gov.uk/pubns/indg408.pdf 32_Smedley_Chap32.indd 647 1/2/2013 12:54:30 PM CHAPTER 32 Prevention and control of exposure 648 Recording the examination and testing of local exhaust ventilation plant A suitable record of each thorough examination and test of LEV should contain the following details \200 The name and address of the employer \200 The identi \201 cation (and lo cation) of the LEV, and the process and substances concerned The dates of the examination and test \200 The process conditions at the time of test, e. g. normal \200 Diagram of the LEV system showing position of hood, \201 lter, fan and test points Information about the LEV plant which shows: its intended operation performance for controlling adequately \200 exposure to hazardous substances \200 whether the LEV is still achieving the same performance \200 if not, th e adjustment or repairs needed to achieve that performance Methods used to make the judgment of performance \200 Results of any air sampling relevan t to LEV performance \200 Name, job title, and employer of the person carrying out the examination and test Observation on the way the operator used the LEV \200 Signature of person carrying out th e test. The employer should have a LEV \200\230user manual \200\231 and a system \200\230logbook \200\231 \200 These documents should be supplied as part of the design, installation, and commissioning process The maximum time between tests for most LEV systems is 14mths (see b p. 532, Control of Substances Hazardous to Health Regulations Regulations 2002) The employer should keep the examination and test report for at least 5yrs. 32_Smedley_Chap32.indd 648 1/2/2013 12:54:30 PM This page intentionally left blank CHAPTER 32 Prevention and control of exposure 650 Personal protective equipment: legal requirements and use De \201 nition PPE is de \201 n ed as all equipment (including clothing) that is intended to be worn or held by a person at work, and which protects him/her against one or more risks to his health or safety. Legal requirements See PPE at Work Regulations 1992 (as amended) Personal protective equip- ment: legal requirements and use, PPE at Work Regulations 1992. The law governing the use of PPE in other speci \201 c regulations is contained in: \200 PPE at Work Regulations 1 992 COSHH 2002 (as amended) \200 Control of Asbestos at Work Regulations 2002 (as amended ) \200 Control of Lead at Work Regulations 2002 \200 Ionizing Radiation at Work Regulat ions 1999 \200 Con \201 ned Spaces Regulations 1997 \200 Control of Noise at Work Regu lations 2005 \200 Construction (Head Protection) Regulations 1989. 1 PPE is considered as the last resort to protect against risks to health and safety. Thus there is a need to dem onstrate \201 rst that the risk cannot be controlled adequately by other means. Use of PPE \200 Effective protection is only achieved by suitable PPE, correctly \201 t ted and maintained, and properly used PPE is used widely, but should be considered as the last resort as: it only reduces exposure for the individual wearer, whereas control at source protects all those in the area the actual level of protection is dif \201 cult to assess \200 it may interfere with wor k tasks/practice \200 it may be uncomfortable and restrict the wearer, limiting movement, and visibility. PPE should be selected and used after justi \201 cation for its use has been made in the r isk assessment. For example RPE can be used in the following situations: \200 where inhal ation exposure remains despite use of other controls, i.e. used minimize residual risk where there is short-term or infrequent exposure and use of other controls is not practical as an interim measure, e.g. when putting in place other controls \200 for emergency respo nse, e.g. safe exit or emergency rescue \200 for emergency work/when there is temporary f ailure of controls. Setting up a effective PPE program Having assessed the risk and implemented all reasonable control meas- ures, the following steps should be considered when setting up a PPE program. 32_Smedley_Chap32.indd 650 1/2/2013 12:54:30 PM PPE: LEGAL REQUIREMENTS AND USE 651 Identify individuals/tasks/environment where PPE is needed \200 Select appropriate PPE to control residual exposure \200 Involve worker in the PPE selection process \200 Match PPE to each individual wearer \200 Carry out \201 t tests for respiratory protective eq uipment (RPE) \200 Ensure the use of PPE does not create additional risks \200 Ensure t hat the PPE is compatible with other PPE \200 Minimize PPE use time by de \201 ning when it should be used, e.g. particular tasks Train the wearer in the correct use of their PPE and supervise use \200 Inspect PPE to en sure it is correctly maintained \200 Provide suitable storage facilities to prevent conta mination \200 Record: PPE issue, maintenance, inspection, and RPE \201 t-testing data \200 Inform individuals of the need for PPE, consequences of PPE failure and the importance of reporting PPE defects. 32_Smedley_Chap32.indd 651 1/2/2013 12:54:30 PM CHAPTER 32 Prevention and control of exposure 652 Selecting respiratory equipment The decision to use RPE should be justi \201 ed in a risk assessment. When selecting RPE consideration must be given to: \200 Individual factors : health status, e.g. cardiorespiratory problems \200 Contaminant : form of substance, sing le substance/mixture, nature of release (energy), concentration and variation, toxicity, OEL Task : duration, other PPE used, mobility, manual dexterity, visibility, communication, work rate (metabolic rate) Environment : indoor/outdoor, temperature, humidity \200 Legal requirements : CE marking, employer and employee duties \200 Costs : equipment, training, testing, repair/replacing storage, and record keeping.