The respirable fractions from 46 different crushed
amphibole samples were separated by water elutriation. The dimensions of approximately 200 elongate
mineral particles (EMPs) longer than 5 μm in each of these fractions were measured by transmission electron microscopy (TEM). The data were used to address three questions: 1. Can
amphiboles be classified on a scale that represents the level of inhalation hazard they present? 2. Can prismatic
amphibole be discriminated from
amphibole asbestos on the basis of EMP size distributions and concentration measurements? 3. How do different exposure indices (Phase Contrast Microscopy Equivalent (
PCME), Berman & Crump protocol fibers, Chatfield extra-criteria EMPs) compare when applied to these
amphibole samples? For each sample, the number of respirable EMPs longer than 5 μm per gram of respirable dust and the number of extra-criteria EMPs per gram of respirable dust were calculated. The number of respirable EMPs longer than 5 μm per gram of respirable dust and the proportion of those with dimensions associated with
mesothelioma in animal studies were considered to be contributors to the inhalation hazard presented by
amphibole dust. In addition to these concentration measurements, the median EMP width, median aspect ratio and the aspect ratio geometric standard deviation (GSD) were considered to be relevant parameters in discriminating prismatic
amphibole from asbestiform
amphibole. A plot of the aspect ratio GSD against either the concentration of respirable EMPs per gram of respirable dust, the median aspect ratio or the median width allowed discrimination. The data showed a close correspondence between exposures in terms of Chatfield extra-criteria EMPs and Berman and Crump protocol structures for all of the
amphibole samples. However, although for commercial
asbestos varieties exposures in terms of
PCME fibers were comparable to those of the other two metrics, they greatly exceeded those for non-asbestiform
amphiboles.