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

Our plain-English summary of Cumulative asbestos exposure for US automobile mechanics involved in brake repair (circa 1950s-2000), by B.L. Finley, R.O. Richter, F.S. Mowat, et al (Journal of Exposure Science & Environmental Epidemiology, 2007).

The study

• Authors: B.L. Finley, R.O. Richter, F.S. Mowat, S. Mlynarek, D.J. Paustenbach, J.M. Warmerdam, P.J. Sheehan
• Journal: Journal of Exposure Science & Environmental Epidemiology
• Published: 2007;17(7):644-55
• Type of article: Historical article
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We analyzed cumulative lifetime exposure to chrysotile asbestos experienced by brake mechanics in the US during the period 1950-2000. Using Monte Carlo methods, cumulative exposures were calculated using the distribution of 8-h time-weighted average exposure concentrations for brake mechanics and the distribution of job tenure data for automobile mechanics. The median estimated cumulative exposures for these mechanics, as predicted by three probabilistic models, ranged from 0.16 to 0.41 fibers per cubic centimeter (f/cm(3)) year for facilities with no dust-control procedures (1970s), and from 0.010 to 0.012 f/cm(3) year for those employing engineering controls (1980s). Upper-bound (95%) estimates for the 1970s and 1980s were 1.96 to 2.79 and 0.07-0.10 f/cm(3) year, respectively. These estimates for US brake mechanics are consistent with, but generally slightly lower than, those reported for European mechanics. The values are all substantially lower than the cumulative exposure of 4.5 f/cm(3) year associated with occupational exposure to 0.1 f/cm(3) of asbestos for 45 years that is currently permitted under the current occupational exposure limits in the US. Cumulative exposures were usually about 100- to 1,000-fold less than those of other occupational groups with asbestos exposure for similar time periods. The cumulative lifetime exposure estimates presented here, combined with the negative epidemiology data for brake mechanics, could be used to refine the risk assessments for chrysotile-exposed populations.

In plain English

This was an exposure-modeling study, not a study of disease. The authors estimated lifetime chrysotile asbestos exposure for US mechanics repairing brakes on cars and light trucks. Using a computer simulation (Monte Carlo) with three statistical models, they combined 84 personal air samples that NIOSH collected during brake jobs in 22 settings in 1976 and 1987 with US job-tenure data for automobile mechanics. Results are given in f/cm3 year (fibers per cubic centimeter multiplied by years). For 1970s garages, which generally had no dust control, median lifetime exposures ranged from 0.16 to 0.41 f/cm3 year, and 95th-percentile values from 1.96 to 2.79. For 1980s garages, mostly with dust control, medians were 0.010 to 0.012 f/cm3 year. The 1980s 95th-percentile range is printed as 0.06 to 0.09 in one place and 0.07 to 0.10 in others. All estimates were below 4.5 f/cm3 year, the exposure from 45 years at the current US workplace limit of 0.1 f/cm3. The authors concluded that the estimates, together with epidemiology data for brake mechanics, could be used to refine risk assessments for other chrysotile-exposed groups.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Probabilistic (Monte Carlo) exposure-modeling study combining previously published air-sampling data with job-tenure survey data; no health outcomes were studied
• Who was studied: Modeled US brake mechanics working on passenger vehicles and light trucks in commercial garages. Air data: 84 personal samples collected by NIOSH researchers during brake jobs in 22 settings in 1976 and 1987. Job tenure: data for US automobile mechanics from the January 1987 current population survey, as reported by Carey (1988).
• Exposure: Chrysotile asbestos during brake repair. Cumulative exposure was calculated as years worked multiplied by the 8-hour time-weighted average airborne concentration. Data were split into 1970s garages (generally no dust control; also treated as representative of earlier decades) and 1980s garages (mostly with dust control).
• Main results:
  • Median cumulative exposure for 1970s garages was 0.16 to 0.17 f/cm3 year with low brake activity (4 or fewer brake jobs a week) and 0.37 to 0.41 f/cm3 year with high activity (8 or more a week)
  • Upper-bound (95th percentile) cumulative exposures were 2.63 to 2.79 f/cm3 year for all 1970s data, 1.96 to 2.49 for low-activity 1970s data, and 2.69 to 2.71 for high-activity 1970s data. These were all at least 10 times higher than the 1980s upper bound, given in this section as 0.06 to 0.09 f/cm3 year.
  • For mechanics in garages with dust-control measures, median cumulative exposure was 0.010 to 0.012 f/cm3 year and the upper bound was 0.07 to 0.10 f/cm3 year (as stated in the Summary section)
  • All model estimates were below 4.5 f/cm3 year, the cumulative exposure from 45 years at the current OSHA limit of 0.1 f/cm3
  • Over 95% of modeled US brake mechanics had cumulative lifetime chrysotile exposures below 3 f/cm3 year
  • Projected job tenure for US automobile mechanics was a median of 6.3 years and a mean of 11.0 years (95th percentile 36.0 years, 99th percentile 49.1 years)
  • Mean values for US mechanics (0.28 to 0.36 f/cm3 year) were lower than the 1.8 f/cm3 year average of three earlier European studies. The authors attributed this mainly to longer job tenure in Europe.
  • Compared with other asbestos-exposed occupations (data taken from Hodgson and Darnton, 2000), brake mechanics' cumulative exposure was between one 100th and one 1,000th as large
• The authors' conclusion: The authors concluded that the cumulative exposure estimates and epidemiology data for brake mechanics could be used to refine risk assessments for other chrysotile-exposed populations
• Limitations the authors state:
  • Job tenure data specific to brake mechanics were not available, so tenure data for all automobile mechanics were used
  • Cross-sectional tenure surveys do not capture time worked after the survey and undersample short tenures, which required adjustment
  • The 1980s data could not be split by brake-job activity level because activity was not reported

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Chrysotile, Cumulative Exposure, Time-Weighted Average (TWA), Fibers per Cubic Centimeter (f/cc), Engineering Controls, Occupational Exposure, Epidemiology.

Related studies

• Asbestos-related diseases in automobile mechanics — J. Ameille, N. Rosenberg, et al. (2012)
• Chrysotile asbestos exposure associated with removal of automobile exhaust systems (ca. 1945-1975) by mechanics: results of a simulation study — D.J. Paustenbach, A.K. Madl, et al. (2006)
• An evaluation of short-term exposures of brake mechanics to asbestos during automotive and truck brake cleaning and machining activities — R.O. Richter, B.L. Finley, et al. (2009)
• Exposure to chrysotile asbestos associated with unpacking and repacking boxes of automobile brake pads and shoes — A.K. Madl, L.L. Scott, et al. (2008)
• Asbestos exposure among transmission mechanics in automotive repair shops — N. Salazar, M.F. Cely-García, et al. (2015)
• Evaluation of exposure to the airborne asbestos in an automobile brake and clutch manufacturing industry in Iran — H. Kakooei, H. Marioryad (2010)

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