Airborne asbestos concentration from brake changing does not exceed permissible exposure limit

Our plain-English summary of Airborne asbestos concentration from brake changing does not exceed permissible exposure limit, by C.L. Blake, D.R. Van Orden, M. Banasik, et al (Regulatory Toxicology and Pharmacology, 2003).

The study

• Authors: C.L. Blake, D.R. Van Orden, M. Banasik, R.D. Harbison
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2003;38(1):58-70
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The use in the past, and to a lesser extent today, of chrysotile asbestos in automobile brake systems causes health concerns among professional mechanics. Therefore, we conducted four separate tests in order to evaluate an auto mechanic's exposure to airborne asbestos fibers while performing routine brake maintenance. Four nearly identical automobiles from 1960s having four wheel drum brakes were used. Each automobile was fitted with new replacement asbestos-containing brake shoes and then driven over a predetermined public road course for about 2253 km. Then, each car was separately brought into a repair facility; the brakes removed and replaced with new asbestos-containing shoes. The test conditions, methods, and tools were as commonly used during the 1960s. The mechanic was experienced in brake maintenance, having worked in the automobile repair profession beginning in the 1960s. Effects of three independent variables, e.g., filing, sanding, and arc grinding of the replacement brake shoe elements, were tested. Personal and area air samples were collected and analyzed for the presence of fibers, asbestos fibers, total dust, and respirable dust. The results indicated a presence in the air of only chrysotile asbestos and an absence of other types of asbestos. Airborne chrysotile fiber exposures for each test remained below currently applicable limit of 0.1 fiber/ml (eight-hour time-weighted average).

In plain English

This experimental industrial hygiene study recreated 1960s-style brake work. The authors bought four 1960s Chevrolet Impalas with four-wheel drum brakes, fitted them with new chrysotile asbestos-containing brake shoes, and drove them about 2253 km (1400 miles) near Pittsburgh, Pennsylvania. In 2001, one experienced mechanic replaced the brakes in a closed former repair shop using 1960s tools and methods, including blowing out dust with compressed air. Six brake changes were sampled: two baseline jobs, one with filing, one with sanding and two with arc grinding of the new shoes. A shop cleanup was also sampled. Chrysotile was the only type of asbestos found in the air. The mechanic's exposure was expressed as an 8-hour average, assuming no other exposure that day. It was highest during the two arc grinding tests (0.0935 and 0.0347 fibers per ml) and well below 0.02 fibers per ml in the other brake jobs. No asbestos was detected during cleanup. The authors concluded that blowout, filing and sanding did not expose the worker above the current OSHA 8-hour limit of 0.1 fibers per ml.

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: Experimental (simulation) industrial hygiene study of air sampling during brake replacement
• Who was studied: Four 1960s Chevrolet Impalas (1965, 1966, 1965 and 1968 models) with drum brakes, serviced by one experienced professional mechanic in a former repair facility in New Kensington, Pennsylvania. Six complete brake changes plus one cleaning test were done on July 12–13 and October 19, 2001.
• Exposure: Chrysotile-containing replacement brake shoes. Bulk analysis of one shoe found 30% chrysotile by area; manufacturer data indicated 72% asbestos in primary shoes and 50% by weight in secondary shoes. Tasks were compressed-air blowout, filing, sanding, arc grinding and shop cleaning.
• Main results:
  • Of the asbestos types, only chrysotile fibers were found in the mechanic's personal air samples. Non-asbestos fibers were also counted.
  • The mechanic's highest 8-hour average exposures (phase contrast microscopy equivalent) were during the first and second arc grinding tests: 0.0935 and 0.0347 fibers per ml.
  • All other brake-change tests (baseline, filing, sanding) gave 8-hour averages well below 0.02 fibers per ml for the mechanic. No asbestos was detected during the cleaning test.
  • The 8-hour averages assume no exposure other than the test. During the first arc grinding test itself (103 minutes), the mechanic's average concentration was 0.4358 fibers per ml (phase contrast microscopy equivalent).
  • No asbestos fibers were detected in outdoor air samples taken upwind and downwind of the building.
  • For indoor area samples, there was no statistically significant difference in concentration between samples near the car and those far from it.
  • The mechanic's total dust during brake changes, as 8-hour averages, ranged from 0.193 to 0.708 mg/m3 (mean 0.333 mg/m3). Respirable dust was below the 0.095 mg/m3 detection limit except during filing (0.243 mg/m3) and the second arc grinding test (0.103 mg/m3).
• The authors' conclusion: The authors concluded that replacing asbestos-containing brake shoes, including blowout, filing or sanding, did not expose the worker to airborne asbestos above the existing OSHA 8-hour limit.
• Limitations the authors state:
  • Indoor area air filters became overloaded with dust. This interfered with microscope analysis of those samples, and some area samples could not be counted.
  • The authors called the 1400-mile driving distance a compromise. They noted that at an average brake life of 30,000 miles, wear dust on the backing plates is roughly five times the amount measured at 1400 miles.
  • The new shoes used in the sanding test had no glaze and so were softer than glazed shoes would be.

Topics

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

Medical terms in this study, explained in our Lexicon: Permissible Exposure Limit (PEL), Chrysotile, Brake Lining, Time-Weighted Average (TWA).

Related studies

• Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — M.A. Atkinson, M. O'sullivan, et al. (2004)
• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)
• A study of airborne chrysotile concentrations associated with handling, unpacking, and repacking boxes of automobile clutch discs — G.C. Jiang, A.K. Madl, et al. (2008)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)
• 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)
• 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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