There are many types of exposure limits in use for the workplace depending on the duration a person is exposed to the pollutant. Hence, a dose of a particular pollutant is conveniently expressed in terms of minutes, hours or years. The most widely used limits are: the threshold limit value (TLV) that should never be exceeded, the maximum exposure limit (MEL), the short-term exposure limit (STEL), the occupational exposure limit (OEL) and the long-term exposure limit (LTEL). Industrial exposures that are normally speciﬁed by the Health and Safety Executive in the UK or the Occupational Safety and Health Administration in the USA are based on 40-h working week with 8-10 h per working day. In this chapter the main indoor pollutants are identiﬁed and the rates of outdoor
air ﬂow rates necessary to achieve acceptable pollutant concentrations will be postulated with reference to various ventilation guides and standards. The effectiveness of ventilation systems in removing indoor contaminants is reviewed with reference to the concept of ventilation effectiveness or efﬁciency.