eturned to <strong>the</strong> workroom can be provided bymechanical ventilation such as an aircondition<strong>in</strong>gsystem. Condition<strong>in</strong>g <strong>in</strong>cludesheat<strong>in</strong>g or cool<strong>in</strong>g <strong>the</strong> air, filter<strong>in</strong>g it and, <strong>in</strong>some cases, adjust<strong>in</strong>g <strong>the</strong> humidity to provide<strong>the</strong> most com<strong>for</strong>table work<strong>in</strong>g conditions(see Figure 5).22 This treatment is unlikely to remove allcontam<strong>in</strong>ants. In some cases <strong>the</strong>y may reachsuch high concentrations that <strong>the</strong>y cause healthproblems. This means that you should providean adequate supply of air <strong>in</strong>to <strong>the</strong> system at asufficient rate to replace lost air. This way youcan dilute <strong>the</strong> contam<strong>in</strong>ants us<strong>in</strong>g <strong>the</strong> correctfresh air supply rate.Emergencies23 You must use a risk assessment to decidehow to manage an emergency. This could be aspillage or release of a substance hazardous tohealth, which may be a mist, vapour, gas, fumeor dust, <strong>in</strong>to <strong>the</strong> atmosphere. Depend<strong>in</strong>g on<strong>the</strong> level of risk you may <strong>the</strong>n use generalventilation to dilute <strong>the</strong> air, <strong>for</strong> <strong>in</strong>stanceopen<strong>in</strong>g a w<strong>in</strong>dow to provide rapid ventilationof <strong>the</strong> environment.24 However, when your employees enter anemergency area <strong>for</strong> clean<strong>in</strong>g up <strong>the</strong>y shoulduse o<strong>the</strong>r control measures, <strong>for</strong> examplewear<strong>in</strong>g suitable respiratory protectiveequipment to protect <strong>the</strong>m from potentialexposure to hazardous substances.25 If necessary, ventilation systems whichrecirculate air must be switched off to reduce<strong>the</strong> risk of fire and explosion dur<strong>in</strong>g <strong>the</strong>emergency.6STANDARDS OFGENERAL VENTILATION26 The <strong>Workplace</strong> (Health, Safety and Welfare)Regulations 1992 (WHSW), 8 regulation 6requires that you, <strong>the</strong> employer, do what isneeded to make sure that every enclosedworkplace is ventilated by a sufficient quantityof fresh or purified air.27 The <strong>Guidance</strong> 9 <strong>for</strong> regulation 6 states that<strong>the</strong> fresh air supply rate to your workplaceshould not normally fall below 5 to 8 litres persecond, per occupant. You need to considerseveral factors when decid<strong>in</strong>g <strong>the</strong> appropriaterate <strong>for</strong> your workplace.These <strong>in</strong>clude:<strong>the</strong> amount of floor space availableper occupant;<strong>the</strong> work activity;<strong>the</strong> smok<strong>in</strong>g habits of <strong>the</strong> occupants; andwhe<strong>the</strong>r <strong>the</strong>re are o<strong>the</strong>r sources of airbornecontam<strong>in</strong>ation aris<strong>in</strong>g from processmach<strong>in</strong>ery, heaters, furniture, furnish<strong>in</strong>gs etc.Factories, hospitals, laboratories etc28 If you use general ventilation to controlexposure to a substance hazardous to health, itis important that you choose <strong>the</strong> right airsupply rate. This should reduce <strong>the</strong>concentrations of <strong>the</strong> contam<strong>in</strong>ants to wellbelow <strong>the</strong> appropriate OELs or to a safe levelwhere OELs are not specified so as to protectyour employees from ill health.29 In this case, it is advisable to consult anoccupational hygienist and/or a ventilation
Full recirculation(with condition<strong>in</strong>g)Motorised dampers to controlfresh air <strong>in</strong>take and exhaustThe use of fresh airand recirculated airFigure 5: Examples of recirculation systems7
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