General Ventilation in the Workplace Guidance for Employers

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8engineer or other competent person to decideon the correct ventilation rate and design.Offices, shops, theatres etc30 Employees in offices, shops and in theentertainment industry are exposed tocontaminants arising from many sourcesincluding carpets, furniture, cleaning products,heaters, photocopiers, the building itself, theventilation ducting and from the outsideenvironment.31 General ventilation is needed to removeodours, in particular body odours from people,rather than to reduce adverse health effects.32 The recommended fresh air supply ratesper person are given in the CIBSE Guide A:Environmental Design 10 produced by theChartered Institution of Building ServicesEngineers (CIBSE). These are based on dilutingpersonal odour and cigarette smoke eventhough many companies now operate a 'nosmoking' policy or allocate separate smokingareas.33 A recommended fresh air supply rate of8 litres per second per person should providea clean and hygienic workplace in open planoffices, shops and even factories. Higher freshair supply rates of up to 36 litres per secondper person are recommended for heavilycontaminated buildings ie 70% of peoplesmoking (see CIBSE Guide A 10 ).Standards for gas, coal or oil firedequipment34 If you use gas, coal or oil fired equipment,the fresh air requirements will depend on whatkind of flue arrangement you use. Roomventilation rates can vary considerably for openflue (drawing air from the room and dischargingproducts outside) and unflued appliances(drawing air from and discharging products intothe room). Further details are given in therelevant British Standards (see FurtherInformation).35 Your workers are at risk of gas poisoning,in particular from carbon monoxide, if there isnot enough fresh air in the room to removecombustion products, especially from unfluedcombustion equipment. It is essential that allappliances are expertly installed and receiveregular maintenance and servicing by acompetent person.Air movement36 Air movement caused by general ventilationcan affect comfortable working conditions. Yourworkers will be happier if they can alter theirenvironment, for example by opening or shuttinga window when required. At normal temperaturesan air flow velocity of between 0.1 to 0.15 metresper second and up to 0.25 metres per secondduring the summer is recommended by CIBSE. 10Keep draughts to a minimum.HOW TO ACHIEVEEFFECTIVE VENTILATIONIN YOUR WORKPLACE37 If your workplace is appropriately designed,for example by providing space for flexibility,and if the building is situated where there isenough shade to minimise summer heat,then you should be able to obtain adequatenatural ventilation.
38 In most buildings make up air (air toreplace that lost from the building) will besupplied indirectly through gaps around door?and window frames or directly through vents,windows, grilles and open doors.39 But there are things you can do to makesure you have effective ventilation in yourworkplace:install trickle ventilators in window framesas well as having windows that open toprovide controllable draught freeventilation (it is important that in winter anywindows are well sealed and secure whenclosed) (see Figure 6);keep doors and windows open to provide agood supply of make up air (in winter whenthe doors and windows are shut, you cansupply make up air through air vents andextract any contaminated air using asuitable system eg via roof vents);position fans to extract contaminated airthrough an extraction point downwind or tosupply fresh air on a wall and/or in the roof,in particular if your workplace has a largeinternal space (as in many industrial units,garages and warehouses);use fans on the wall of each side of thebuilding to keep fresh air flowingAir containing contaminantsescapes to atmospherevia roof ventsAir enters andescapes throughgaps aroundbuildingOpen windowsFigure 6. Natural ventilation moving fresh air through a buildingFresh air enters viawindows and/or openingsor vents9
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 8 and 9: Vapour laden air rises toroof where
Page 10 and 11: eturned to the workroom can be prov
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

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