Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a "state-of-the-art" review

Our plain-English summary of Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a "state-of-the-art" review, by D.J. Paustenbach, B.L. Finley, E.T. Lu, et al (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2004).

The study

• Authors: D.J. Paustenbach, B.L. Finley, E.T. Lu, G.P. Brorby, P.J. Sheehan
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2004;7(1):25-80
• Type of article: Review
• Cited by: 45 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Throughout the history of automobile development, chrysotile asbestos has been an essential component of vehicle brake linings and pads. Acceptable alternatives were not fully developed until the 1980s, and these were installed in vehicles produced over the past decade. This article presents a "state-of-the-art" analysis of what was known over time about the potential environmental and occupational health hazards associated with the presence of chrysotile asbestos in brake linings and pads. As part of this analysis, the evolution of automobile brakes and brake friction materials, beginning with the early 1900s, is described. Initial concerns regarding exposures to asbestos among workers involved in the manufacture of friction products were raised as early as 1930. Between 1930 and 1959, eight studies were conducted for which friction product manufacturing workers were part of the population assessed. These studies provided evidence of asbestosis among highly exposed workers, but provided little information on the magnitude of exposure. The U.S. Public Health Service proposed the first occupational guideline for asbestos exposure in 1938. The causal relationship between asbestos exposure and lung cancer was confirmed in 1955 in asbestos textile workers in the United Kingdom, and later, in 1960, in South Africa, mesothelioma was attributed to asbestos exposure to even relatively low airborne concentrations of crocidolite. Between 1960 and 1974, five epidemiology studies of friction product manufacturing workers were conducted. During this same time period, the initial studies of brake lining wear (dust or debris) emissions were conducted showing that automobile braking was not a substantial contributor of asbestos fibers greater than 5 microm in length to ambient air. The first exposure surveys, as well as preliminary health effects studies, for brake mechanics were also conducted during this period. In 1971, the Occupational Safety and Health Administration promulgated the first national standards for workplace exposure to asbestos. During the post-1974 time period, most of the information on exposure of brake mechanics to airborne asbestos during brake repair was gathered, primarily from a series of sampling surveys conducted by the National Institute of Occupational Safety and Health in the United States. These surveys indicated that the time-weighted average asbestos

In plain English

This was a historical "state-of-the-art" review, not a new study. The authors traced chrysotile asbestos in U.S. car brakes from about 1900 to 2002 and summarized exposure and health studies of brake mechanics and friction product manufacturing workers. The work was primarily funded by Ford, DaimlerChrysler and General Motors, companies involved in brake-dust litigation. In NIOSH surveys, time-weighted averages over brake jobs, counting fibers longer than 5 micrometers, ranged from less than 0.004 to 0.28 fibers per cubic centimeter, below OSHA's daily limits of the time. The article noted brief brake-cleaning samples could not be judged against OSHA's short-term ceiling limit. A meta-analysis by another researcher, Wong, of six mesothelioma case-control studies gave mechanics a summary relative risk of 0.90 (95% confidence interval 0.66 to 1.23). In a UK friction-materials factory, 11 of 13 pleural mesothelioma deaths were in workers with known contact with crocidolite. The authors concluded that brake mechanics were not at increased risk of asbestos-related disease. They also concluded that any risk among friction product manufacturing workers was not apparent, except in those with some amphibole exposure.

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: Historical ("state-of-the-art") narrative review of published studies, government surveys, regulations and industry documents, divided into three periods (1900-1959, 1960-1974, 1975-2002). The article states it was primarily funded by Ford, DaimlerChrysler and General Motors, which had been involved in brake-dust litigation.
• Who was studied: Studies of brake mechanics and of friction product (brake lining and pad) manufacturing workers. For 1975 to 2002 alone, the review counted 10 exposure surveys and 25 health studies of brake mechanics, and 11 exposure surveys and 15 health studies of friction material manufacturing workers. The history covers U.S. passenger cars and light trucks.
• Exposure: Chrysotile asbestos in vehicle brake linings and pads. The authors state chrysotile was the only asbestos type used in brake linings and pads for U.S. passenger cars and light trucks. Exposures arose during brake repair and during manufacture of friction products.
• Main results:
  • In the NIOSH surveys reviewed (19 garages, more than 200 air samples on more than 50 mechanics), brake-job time-weighted average chrysotile concentrations for automobile brake mechanics ranged from less than 0.004 to 0.28 f/cc, counting fibers longer than 5 micrometers.
  • These brake-job averages were all below the OSHA permissible exposure limits, which are daily time-weighted averages, in effect at the time of the studies.
  • Short samples taken during brake cleaning (0.5 to 3 minutes) were shorter than the 15-minute period needed, so the article states they cannot be described as above or below the OSHA ceiling limit of the time.
  • The mean brake-job time-weighted average for mechanics in these NIOSH data was about 0.05 f/cc, a figure taken from the authors' own earlier paper (Paustenbach et al., 2003).
  • Wong (2001), another researcher, pooled six case-control studies of mesothelioma in garage mechanics and reported a summary relative risk of 0.90 with a 95% confidence interval of 0.66 to 1.23.
  • In Teschke et al. (1997), a British Columbia study of 51 pleural mesothelioma cases, relative risk estimates were 0.8 (95% CI 0.2 to 2.3) for vehicle mechanics and 0.3 (95% CI 0.0 to 1.4) for brake lining installation or repair.
  • Lung cancer, Vineis et al. (1988): 98 cases and 90 controls had ever worked as automobile brake workers. The relative risk, adjusted for age, birth cohort and smoking, was 1.2 (95% CI 0.9 to 1.7).
  • Wong's meta-analysis of three cohort studies of lung cancer in garage mechanics reported a relative risk of 1.01 (95% CI 0.8 to 1.26).
  • In Nicholson et al. (1984), a Mount Sinai study of 450 brake repair workers, 124 mechanics without brake repair experience and 205 unexposed controls, there were no statistically significant differences in the prevalence of abnormal chest x-rays between garage workers with and without brake repair experience.
  • At a UK friction-materials factory (more than 13,000 workers, deaths followed 1941 to 1986), 13 deaths were attributed to pleural mesothelioma. Eleven of these workers had known contact with crocidolite before 1945, in the manufacture of railroad brake blocks.
  • In the first brake-wear study (Lynch, 1968, using brake test machines), generally less than 1% of the wear debris particles were chrysotile fibers, even though unused linings contained 30% to 50% chrysotile by weight.
  • The authors judged that friction product manufacturing workers had historically been exposed to chrysotile concentrations perhaps 10 to 50 times greater than those of brake mechanics.
• The authors' conclusion: The authors concluded that the more than 25 epidemiology studies from 1975 to 2002 clearly indicated that brake mechanics were not at increased risk of adverse health effects from asbestos exposure. They concluded that the risk of asbestosis, mesothelioma and lung cancer among friction product manufacturing workers, if any, was not apparent, except among workers who had some amphibole exposure.
• Limitations the authors state:
  • The studies of chrysotile content in brake dust used different methods, so their results must be compared with care.
  • The data from the early period (1900-1959) were inadequate to describe a dose-response relationship for friction product manufacturing workers.
  • The chronology of brake development applies only to U.S. passenger cars and light trucks.
  • The history of braking systems and brake linings is based on previously published summaries.

Topics

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

Medical terms in this study, explained in our Lexicon: Brake Lining, Chrysotile, Friction Products, Asbestos Exposure, Lung Cancer, Mesothelioma, Crocidolite, Epidemiology.

Related studies

• Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): A "state-of-the-art" review — S.S. Paskal (2004)
• 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 during brake lining maintenance and repair — A.N. Rohl, A.M. Langer, et al. (1976)
• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)
• Re: Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — D.J. Paustenbach, B.L. Finley, et al. (2006)
• Asbestos in brakes: exposure and risk of disease — R.A. Lemen (2004)

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