The effects of sampling practice on the measured concentration of airborne asbestos

The effect of variations in sampling practice upon the measurement of airborne amosite and chrysotile asbestos fibre concentrations by the membrane filter method has been investigated experimentally in a laboratory dust chamber and to a lesser extent in industrial situations. The parameters tested were sampling flow rate and volume, the pore size and electrostatic charge of the filter and the angle of inclination of the sampling head.

For all types of filter an increase in the sampled volume resulted in a relative lowering of the measured concentration. This was found to be due to an analytical effect and not to changes in sampling efficiency of the filter. The collection of fibres without a sampling flow accounted for 10% of a sample taken at 200 ml min −1 . This effect is therefore only relatively important at very low flow rate.

Large (8 μm) pore size membrane filters, when sampling amosite at 21. min −1 , produced a fibre count approximately 15% lower than equivalent measurements on 0.8 μm pore sized filters, although there was no significant fibre penetration completely through this type of filter. Approximately 20% of both amphibole and chrysotile fibres, however, passed through an 8 μm pore size Nuclepore filter at this sampling rate.

The electrostatic charge on the filter and the angle of inclination of the sampling head did not appear to significantly affect the measurements.