General
18. The lists of occupational exposure limits given in Table 1 and Table 2 of Annexure 1, unless otherwise stated, relate to personal exposure to substances hazardous to health in the air of the workplace.
Units of measurement
19. In occupational exposure limits, concentrations of gases and vapours in air are usually expressed in parts per million (ppm), a measure of concentration by volume, as well as in milligrams per cubic metre of air (mg/m³), a measure of concentration by mass. In converting from ppm to mg/m³ a temperature of 25°C and an atmospheric pressure of 101.325 kPa are used. Concentrations of airborne particles (fume, dust, etc.) are usually expressed in mg/m³. In the case of dust, the limits in the tables refer to the total inhalable fraction unless specifically indicated as referring to the respirable fraction (see paragraph 36). In the case of a man-made mineral fibre, the limit is expressed as fibres per millilitre of air (fibres/ml).
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