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Airborne dust from each of several common types of chrysotile-containing materials was generated by abrasion of the material at the base of a vertical elutriator. Air samples were collected on membrane filters situated at the top of the elutriator. The upward linear velocity within the elutriator was selected such that respirable particles and fibers were collected on the membrane filters, while larger, non-respirable particles and fibers fell to the horizontal surface below the base of the elutriator. Transmission electron microscope (TEM) specimens were prepared from the membrane filters by both ISO 10312 and ASTM D5755-95. TEM specimens were also prepared from the settled dust using the technique specified in ASTM D5755-95. The results show that most of the chrysotile structures detected on the TEM specimens prepared from the settled dust samples were of such sizes that their falling speeds would be very much lower than the vertical air velocity in the elutriator. Individual chrysotile structures of these dimensions, therefore, could not have been present in the original dust and debris which settled. The numbers, sizes and characteristics of the chrysotile structures reported by the ASTM D5755-95 method were therefore not representative of the particles as they existed on the original surface, nor of the airborne respirable particles generated by abrasion of the original material. It is also concluded that simple resuspension factor calculations using surface dust measurements, made by either ASTM D5755-95 or D5756-95, do not provide a valid scientific basis for prediction of airborne chrysotile concentrations.
Asbestos, chrysotile, air, dust, fiber, transmission electron microscopy, resuspension, k-factor, falling speed
Chatfield, Eric J.
President, Chatfield Technical Consulting Limited, Mississauga, Ontario