Measuring the Dust Levels

The highest measured dust levels occurred during the removal of the brake drum. Since this dust contained ground-up brake shoe (which may or may not be asbestos), this activity was assumed to have the highest potential exposure for asbestos.

The second and third highest measured dust levels occurred during the removal and remounting of the wheels and lug bolts. Since most of this dust came from accumulated road dirt on the wheel and probably contained little asbestos, this activity was assumed to have a low potential asbestos exposure.

The measured dust levels for all other brake servicing activities were near background levels; these activities were a low potential source for asbestos exposure.

Real-time data indicated that thorough washing of the brake support plate, brake shoes, and gear used to attach the brake shoes reduced dust levels. It appeared that the dust was either removed or wetted before the operator started to manually manipulate the brakes. As a result, dust levels were low or not measurable during 91% of the brake shoe service.