Asbestos dust exposure during brake repair

Abstract

About 10,000 tons of chrysotile per year are used in the Federal Republic of Germany for the production of friction materials. During brake repair an unknown number of approximately 300,000 mechanics in automobile service stations are exposed to asbestos dust. In a field study, asbestos fiber concentrations during brake repair were measured. Occupational histories and chest X-rays of brake service mechanics are being examined. Ninety dust measurements in 76 service stations were made by phase contrast microscopy and by scanning transmission electron microscopy. By electron microscopy, extremely fine chrysotile fibers with lengths less than 5 microns were identified in brake drum dust. Fibers with lengths greater than or equal to 5 microns constituted less than 1% of all chrysotile fibers counted in brake drum dust. Short-term asbestos dust exposures were measured by light microscopy in 101 personal samples during blowing out of brakes, and grinding and turning of brake linings. During blowing out of car brakes, as well as during grinding of brake linings, the product of fiber concentration with length greater than 5 microns and sampling time amounted to about 4-5 fibers/ml X min corresponding to a concentration of 10(6) fibers/m3 over 4-5 min. For trucks and buses higher amounts of 5-10 X 10(6) fibers/m3 X min were observed during these operations. From occupational histories of 210 vehicle mechanics, an average duration of employment of mean +/- s = 21 +/- 10 years and a mean cumulative fiber dose of mean +/- s = (0.54 +/- 1.1) X 10(6) fibers/m3 X years were calculated.

Cumulative asbestos exposure for US automobile mechanics involved in brake repair (circa 1950s–2000)

“…These authors found no statistically significant differences between 8-h TWA concentrations experienced by US versus Swedish brake mechanics (Plato study) in the late 1970s/ early 1980s time frame (such a comparison cannot be conducted for the Ro¨delsperger et al (1986) data, because data for individual mechanics were not provided.) Therefore, the lower cumulative lifetime exposure estimate for US brake mechanics is more likely to be attributable to shorter job tenure (as compared with European mechanics) than to differences in airborne chrysotile concentrations.…”

“…Plato et al (1995) estimated a mean annual asbestos concentration of 0.09 f/cm 3 (range, 0.01-0.46 f/cm 3 ) in car mechanics. Ro¨delsperger et al (1986) calculated mean exposure concentrations of car and truck mechanics as 0.04 and 0.08 f/cm 3 , respectively, based on a combination of activities. In the Gustavsson et al (1990) study, data from garages were used to estimate asbestos concentrations for three levels of exposure: 0.0, 0.08, and 0.16 f/cm 3 .…”

“…For example, Plato et al (1995) reported a mean employment of 29 years (range, 20-48 years) and a mean exposure of 26 years (range, 14-48 years) based on company records and subject questionnaires. Ro¨delsperger et al (1986) report that the mean employment duration in German mechanics was 21 years (SD of 10 years).…”

“…Specifically, Ro¨delsperger et al (1986), Gustavsson et al (1990), and Plato et al (1995), using a variety of different techniques, have developed cumulative exposure estimates that are fairly consistent, with mean values ranging from 0.54 to 2.6 f/cm 3 year. However, the applicability of these estimates for US brake mechanics is unclear, because they (1) are derived strictly from airborne data collected in European facilities in Germany and Sweden (Ro¨delsperger et al, 1986;Gustavsson et al, 1990;Dahlqvist et al, 1992); therefore, they do not consider the data collected by NIOSH in 22 US facilities (i.e., Johnson et al, 1979;Roberts, 1980a, b;Roberts and Zumwalde, 1982;Sheehy et al, 1989), and (2) there is some evidence to suggest that the apprentice and journeyman programs used by craftsman, including vehicle mechanics, in Europe (but not in the US) provided a more stable workforce and longer job tenure among workers in these occupations than in equivalent occupations in the US.…”

“…We recently performed a comprehensive analysis of the published industrial hygiene data for brake mechanics (Hickish and Knight, 1970;Johnson et al, 1979;Roberts and Zumwalde, 1982;Ro¨delsperger et al, 1986;Moore, 1988;Sheehy et al, 1989;Plato et al, 1995;Yeung et al, 1999;Roberts, 1980a, b) and determined that the mean 8-h time-weighted average (TWA) asbestos concentration for car and light truck repair was 0.04 fibers per cubic centimeter (f/cm 3 ) (range of o0.001-0.68 f/cc) (Paustenbach et al, 2003) for the period of about 1970 to 1990. It was also determined that airborne TWA asbestos concentrations measured by National Institute for Occupational Safety and Health (NIOSH) in the 1980s time frame for garages with dust control procedures in place in the US were significantly lower than those in the 1970s (mean values of 0.002 and 0.06 f/cm 3 , respectively).…”