Asbestos dust exposure during brake repair

Our plain-English summary of Asbestos dust exposure during brake repair, by K. Rödelsperger, H. Jahn, B. Brückel, et al (American Journal of Industrial Medicine, 1986).

The study

• Authors: K. Rödelsperger, H. Jahn, B. Brückel, J. Manke, R. Paur, H.J. Woitowitz
• Journal: American Journal of Industrial Medicine
• Published: 1986;10(1):63-72
• Cited by: 46 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001149).

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.

In plain English

This German field study measured asbestos exposure during brake repair. The authors took 90 dust measurements in 76 garages using light and electron microscopy. Samples over more than 30 minutes averaged about 0.1 million fibers longer than 5 micrometres per cubic metre for all but one operation. Machine grinding in one truck garage reached 0.39 million per cubic metre over about one hour. Samples under 3 minutes averaged 5.5 million per cubic metre, with a maximum of 20 million. Of 1,219 longer fibers analysed, 74% were chrysotile. Fibers 5 micrometres or longer were under 1% of chrysotile fibers counted in brake drum dust. Work histories were analysed for 210 mechanics with at least 10 years of brake work. Counting only fibers longer than 5 micrometres, their average cumulative dose was 0.54 million fibers per cubic metre times years (standard deviation 1.1), median 0.3. Chest X-ray results were not reported. The authors concluded that concentrations were low and, for sampling of at least one hour, considerably below the German Technical Guiding Concentration of 1 million such fibers per cubic metre. They noted high uncertainty from low fiber counts.

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: Field study of asbestos dust measurements during brake repair, combined with standardized occupational histories from an ongoing cross-sectional study of vehicle mechanics. Chest X-rays were being examined, but no X-ray results are reported.
• Who was studied: Dust measurements were taken in 76 garages in the Federal Republic of Germany: 36 servicing passenger cars and 40 servicing trucks or buses. Occupational histories came from 210 vehicle mechanics with at least 10 years of brake maintenance, out of about 400 the authors intended to examine. The histories described 459 job profiles.
• Exposure: Asbestos (chrysotile) dust released from brake linings during brake repair. Operations included blowing out dust with compressed air, dry brushing, riveting, grinding by hand and by machine, and turning of brake linings.
• Main results:
  • In 67 personal samples taken over more than 30 minutes, average concentrations of fibers longer than 5 micrometres (light microscopy) were about 0.1 x 10^6 fibers per cubic metre (0.1 fiber/ml) for all but one operation.
  • The highest of these longer-term averages was 0.39 x 10^6 fibers longer than 5 micrometres per cubic metre. It was measured during machine grinding of brake drum linings in a truck garage, with a sampling time of about 1 hour.
  • For 14 short-term measurements with sampling time under 3 minutes, the maximum concentration was 20 x 10^6 fibers per cubic metre and the average was 5.5 x 10^6 fibers per cubic metre.
  • Fiber dose is concentration multiplied by sampling time. From 40 measurements during car repair, average doses were about 4 x 10^6 fibers per cubic metre times minutes for dry brushing and grinding, and 5 x 10^6 for blowing out. Doses during truck and bus repair were generally higher, about 10 x 10^6 for machine grinding.
  • By electron microscopy, doses of chrysotile fibers were higher. Three measurements during blowing out of truck drum brakes averaged 20 x 10^6 fibers per cubic metre times minutes.
  • Of 1,219 fibers 5 micrometres or longer from air samples in repair garages, 74% were identified as chrysotile.
  • In brake drum dust, fibers 5 micrometres or longer made up less than 1% of all chrysotile fibers counted.
  • The 210 mechanics had worked as car mechanics for an average of 21 years (standard deviation 10).
  • Among the 210 mechanics, the median cumulative dose of fibers longer than 5 micrometres was 0.3 x 10^6 fibers per cubic metre times years. For about 13% it exceeded 1 x 10^6. For 7% there was no measurable dose because they were exposed only as bystanders.
  • The average cumulative dose of fibers longer than 5 micrometres for the 210 mechanics was 0.54 x 10^6 fibers per cubic metre times years, with a standard deviation of 1.1 x 10^6. The authors said this corresponds to about 6 months of exposure at 1 x 10^6 fibers per cubic metre.
• The authors' conclusion: The authors concluded that brake service involved low fiber concentrations, typically about 0.1 x 10^6 fibers per cubic metre, and mainly short-term exposure. All results were considerably below the German Technical Guiding Concentration (TRK) of 1 x 10^6 fibers longer than 5 micrometres per cubic metre when sampling lasted at least 1 hour. They stated that the average cumulative dose was about one order of magnitude lower than their estimate for roofers cutting asbestos cement, and about one order of magnitude above environmental exposure.
• Limitations the authors state:
  • Fiber counts for certain operations were low, giving a high uncertainty factor.
  • How often different operations were performed, taken from standardized occupational histories, was highly uncertain. The authors said this had no great influence on the calculated cumulative dose.
  • Fiber counting by light microscopy does not distinguish asbestos from other fibers; metal and other fibers may also be released from brake linings.
  • Working conditions had changed over time (precut linings, less machine grinding, more exhaust ventilation). The authors said these changes must be considered when calculating cumulative doses.

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: Chrysotile, Chest X-Ray, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Personal Breathing Zone Sample, Brake Lining.

Related studies

• Exposure to brake dust and malignant mesothelioma: a study of 10 cases with mineral fiber analyses — K.J. Butnor, T.A. Sporn, et al. (2003)
• Asbestos exposure during brake lining maintenance and repair — A.N. Rohl, A.M. Langer, et al. (1976)
• Asbestos content of dust encountered in brake maintenance and repair — A.N. Rohl, A.M. Langer, et al. (1977)
• Assessing specific causation of mesothelioma following exposure to chrysotile asbestos-containing brake dust — M.D. Freeman, S.S. Kohles (2012)
• Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure — D.M. Bernstein, R.A. Rogers, et al. (2015)
• 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)

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