B. MEASUREMENTS OF AIRBORNE ASBESTOS DUST BY THE MEMBRANE FILTER METHOD ° (a) SAMPLING TECHNIQUE 1. SCOPE i The methods adopted by the o.s.H.A.!, N.1.0.8.H.2, and ea ag? of the U.S. government for the definition of airborne asbestos fibre concen- trations have now been generally accepted. This test method describes in detail the Membrane Filter Method of sampling air and the procedure to be followed for analysing the dust deposit obtained from the sample. It is generally only suitable for measuring concentrations encountered occupationally. This method is used for measuring dust concentrations as required by the B.C. government. 2. APPARATUS = Filter holder: A standard 37 mm acrylic plastic filter holder. = Filters: A 37 mm diameter, 0.8 jm pore size cellulose acetate membrane filter is used. = Pump: A portable vacuum pump capable of maintaining a sampling rate of 2lpm for a period of up to four hours is required. A bypass valve is connected across the vacuum pump to allow for control of the sample flowrate. ; = Rotameter: A calibrated rotameter accurate to + 2% is required for adjustment of the flowrate through the filter unit. = Temperature gauge: A thermometer is required which will measure ambient temperatures to within + 1° C. = Barometer: A barometer capable of measuring absolute atmospheric pressure to within 0.1 in. Hg. is required. 3% DEFINITIONS = Fibre: Fibres are defined as being of a length greater than 5 gm and having a length/breadth ratio of at least 3:1. There is no upper limit for the length of the fibres, but a maximum diameter of 3 um is defined. Airborne asbestos dust concentrations are expressed in fibres per millilitre of air (f/ml). 4