Abstract
The NIOSH method for determining asbestos exposure in the mining environment involves using phase contrast microscopy to examine mineral particulates collected on air monitor filters. Particles are classified as asbestiform or non-asbestiform based on their size and length-to-width (aspect) ratio. The procedure works well when only fibers are present. In most non-asbestos mining operations, however, cleavage fragments are the most abundant airborne particulates. In this research, discriminate function analysis was applied to morphological data for airborne amphibole particulates to show that dimensional criteria could distinguish between amphibole asbestos and amphibole -cleavage fragments. The particulates for this research were collected from industrial sites where amosite alone was in use and from mining sites where amphiboles are major rock-forming minerals. The results suggest that cleavage fragments can be differentiated from asbestos fibers based on dimensional criteria alone, but only if the current working definition of a fiber is modified. The data suggest that an appropriate definition of a regulatory fiber would be a particle longer than 5 µm with a width less than 3 µm and an aspect ratio of 20:1 or greater. Adoption of the 20:1 aspect ratio would greatly increase the precision of the NIOSH method. However, a new aspect ratio criterion must be coupled with a lower exposure index in order to prevent an increase in worker exposure to asbestos.