Evaluation of airborne asbestos concentrations using TEM and SEM during residential water tank removal

The purpose of this study was to evaluate three different analytical techniques for estimating concentrations of airborne asbestos during a short-term removal operation. Samples were collected during the removal of asbestos-insulated water tanks. The tank insulation consisted of chrysotile mixed with glass fibre and cellulose. The short time-span, less than 40 min, combined with low level of release of asbestos fibre expected, made the operation difficult to evaluate. The large air samples needed for adequate quantitative assessment were collected using high flowrates for short periods. Airborne samples were collected for phase contrast optical, and scanning and transmission electron, microscopic (PCOM, SEM and TEM) analysis, using direct transfer techniques.

Membrane filter samples collected for PCOM analysis were rejected because of excessive particle loading. The mean chrysotile asbestos fibre concentrations determined, by the European Reference Method (ERM) of fibre counting, and using SEM at 10 000 x and TEM at 2200 x, were 0.12 and 0.11 f ml −1 , respectively. A comparison of side-by-side samples suggested that TEM analysis might be indistinguishable from SEM for ERM fibre counting. The results indicated, however, that when total asbestos fibres were counted TEM analysis provided consistently greater estimates of concentrations of airborne fibres.