Extending the TEM methods designed for the evaluation of atmospheres in which any primary mineral fibers present are derived from a commercial asbestos fiber is a challenging task. This is because the methods employed leave it to the expertise of the user to identify and evaluate interferences. Improper analysis of nonconstruction materials for asbestos content often results in the misidentification of non-asbestos amphibole particles as asbestos fibers. These errors have received widespread publicity in the media (such as the asbestos-in-crayons story) and have caused unwarranted reformulation of harmless products. The primary cause of these errors has been a poor understanding of mineralogy and analytical techniques among the many asbestos laboratories that arose following the passage of the 'Asbestos Hazardous Emergency Response Act' (AHERA) regulations. This study outlines a procedure based on published data that can be used to correctly classify a microscopic, elongated particle as either asbestos or non-asbestos.

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Amphibole asbestos fibers and non-asbestos amphibole particles have been shown to have different size characteristics, in addition to their morphological differences. There is a tendency, however, among laboratories and some regulators to ignore the morphological differences and to simply rely on a minimal aspect ratio to determine whether a particle is an asbestos fiber. This study, part of a larger evaluation of amphibole minerals, was undertaken to provide supporting size data that can be used to identify populations of asbestos and non-asbestos amphibole minerals. The asbestos samples average 0.27 mm in width with 90% thinner than 0.5 mm. In contrast, the non-asbestos amphiboles average 0.97 mm wide with 75% wider than 0.53 mm. The average aspect ratios were 76 : 1 for asbestos and 16 : 1 for the nonasbestos samples. These data confirm the historical distinctions of asbestos and non-asbestos amphibole minerals.

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A detailed evaluation of 122 air samples collected in and around Libby, Montana and previously analyzed by EPA has been performed. Photographic records of each analyzed particle were collected and archived in a searchable database. The results of the study indicate that the EPA’s failure to follow generally accepted procedures overestimated the concentration of regulated asbestos fibers by 10 times and by 3 times for all asbestiform fibers. These results are applicable to the analysis of naturally occurring asbestos in all parts of the country. The results demonstrate the need for detailed morphological and chemical analyses to reliably determine potential exposures and associated risks when evaluating mixed asbestos/non-asbestos environments.