General Ventilation in the Workplace Guidance for Employers

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Vapour laden air rises toroof where it accumulatesor escapes through roof ventIf ventilation is notsufficient, the vapourwill collect in the roofspace or drift back downVapour which doesnot escape may hangin stratified layerCool air enters atlow level throughopen windowsHot process producingfumesCool air enters atlow level throughopen windowsFigure 3: Stack ventilation to remove vapours through roof ventilatorsventilators or extraction fans. If cooler air comesin at a low level, it will displace the warm risingcontaminated air, ie displacement ventilation(see paragraph 20)(see Figure 3).WHEN TO USEGENERAL VENTILATION16 To ensure a well ventilated workplace youshould provide general ventilation that removesstale, contaminated, or hot and humid air so thatyour employees do not suffer any ill-healtheffects. There is guidance on how you canensure thermal comfort at your workplace in theHSE publication Thermal comfort in the workplace. 417 You may consider using effective naturaland/or mechanical general ventilation toprovide the fresh air supply.18 As an employer, if you carry out industrial ornon-industrial work processes (eg hairdressing,catering) you will be required to undertake arisk assessment under the COSHH Regulations.This means assessing the risks to health of youremployees who may be potentially exposed tosubstances hazardous to health. You may thenneed to prevent or adequately control suchexposure.4
19 If the contaminant is of such a low toxicityand produced in such low concentrations that itwould be impractical and costly to use localexhaust ventilation, you may decide to usegeneral ventilation as part of your controlstrategy (see HSE publication COSHHEssentials). 5 However, if there are a smallnumber of well-spaced contaminant sources,using LEV may be more cost effective thangeneral ventilation (see Figure 4). There maybe instances where intermittent exposure to asubstance exceeds the assigned OccupationalExposure Limit (OEL), for example duringwelding and paint spraying. In this case, youshould consider using LEV to control exposure.20 When you use general ventilation to controlexposure to contaminants generated fromindustrial processes, it is essential that:the rate of contaminant produced is lowenough for it to be effectively diluted bythe airflow rate;the contaminant has a low toxicity (see theChemicals (Hazard Information andPackaging for Supply) (Amendment)Regulations 1999 6 );the contaminant is produced at auniform rate;the workers are positioned at 90° to the airflow (the contaminant air must not be drawnor blown towards the faces ofthe operatives);the contaminant is generated in lowconcentrations and can be controlled to theassigned OEL (see HSE publicationEH40/2000 7 ) ; andthe air flow does not affect the performanceof other extraction systems eg fumecupboards, LEV.Use of recirculated air21 You may want to use recirculated air toconserve energy costs. The extracted airDilutionventilationremoves anyairbornecontaminantswhen lids areremovedLocal exhaustventilation isused tocontrolhazardoussubstancesFigure 4: A factory using a combination of local exhaust ventilation and dilution ventilation to control airborne contaminants5
Page 2 and 3: GENERAL VENTILATIONG U I D A N C E
Page 4 and 5: CONTENTSINTRODUCTION 1WHAT IS GENER
Page 6 and 7: Extractor fanin roofFresh airsupply
Page 10 and 11: eturned to the workroom can be prov
Page 12 and 13: 8engineer or other competent person
Page 14 and 15: throughout the building ie one extr
Page 16 and 17: WHAT THE LAWREQUIRES YOU TO DO49 Th
Page 18 and 19: FURTHERINFORMATIONHSE publicationsA
Page 20 and 21: Printed and published by the Health

General Ventilation in the Workplace Guidance for Employers

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