A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards

A comparison has been made of the size distributions of airborne fibres at different locations in two major manufacturing plants using amosite asbestos. Side-by-side samples were taken on membrane and Nuclepore filters; the membrane filters were examined using optical phase microscopy and the length distributions of fibres longer than 5 μm measured. The Nuclepore filter samples were examined using scanning electron microscopy and the lengths of fibres greater than 0.6 μm with diameters of more than 0.2 μm were determined. No major differences were found in size distribution either at the different sites or due to the analytical technique used, except for samples taken in relatively high velocity air streams. The effect of a change from the present standard in length or aspect ratio of the fibres counted on the measured concentration is discussed.