Comparison of methods of assessing asbestos fiber concentrations

Dimensional measurement of the counted fibers has important implications for setting of environmental standards to protect workers' health. Results of fiber concentrations as determined by different methods were compared. Each method was used to determine concentration by examining one sector of membrane filter on which fibrous dust was collected in various workplaces. The concentrations measured by the Asbestos International Association (AIA) method for 35 samples were, on the average, greater than the concentrations determined by the modified British Occupational Hygiene Society--Asbestosis Research Council (BOHS-ARC) method. The AIA and modified BOHS-ARC methods were found to be linearly correlated (r = 0.82). The mean of total fiber concentrations obtained by using the indirect transmission electron microscopy (TEM) method was 15.5 times the mean obtained by using the direct TEM method. The difference in concentrations determined by the two TEM methods resulted from disintegration of fiber bundles into single fibers during the ashing and ultrasonifying processes used in the indirect method. At least 83.5% of total fibers observed by TEM escaped detection by phase contrast microscopy.