Morphological characteristics of asbestos fibers released during grinding and drilling of friction products.

There has been considerable interest during the past 30 years regarding the potential for exposure to asbestos fibers generated during asbestos-containing automobile and light-duty truck brake replacement and repair operations. Less attention has been directed to asbestos fiber exposures resulting from servicing of brakes on heavy-duty trucks and other machinery. Potential for the generation of respirable fibers as a result of using a rotary bench grinder and the drilling of asbestos-containing friction pads was investigated to assess the characteristics of the fibers generated from these procedures. The data from the grinding process revealed that this material was either resin matrix or fibers bound to the resin matrix. Fibers generated from the drilling procedure revealed morphology consistent with chrysotile asbestos. In each case, nonfibrous materials remained bound to the fibers released from these processes. These fibers had resin deposits attached. This investigation offers evidence that drilling and grinding of brake pads generates fibers that, for the most part, remain bound to the underlying matrix, suggesting that grinding and drilling may not pose an important source of exposure to respirable asbestos fibers.