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