Asbestos Exposure Of Brake Repair Workers In The United States

Our plain-English summary of Asbestos Exposure Of Brake Repair Workers In The United States, by W.V. Lorimer, A.N. Rohl, A. Miller, et al (1976).

The study

• Authors: W.V. Lorimer, A.N. Rohl, A. Miller, W.J. Nicholson, I.J. Selikoff
• Published: Mount Sinai Journal Of Medicine 43(3):207-218, May-June (1976)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 002296. The article is still under copyright, so we describe it here rather than post it.

In plain English

This New York City study had two parts. First, the authors took peak air samples over 2 to 10 minutes during brake jobs on cars and trucks. They counted fibers longer than 5 microns by optical microscopy. Blowing dust out of car drum brakes gave a mean of 15.9 fibers/ml at 3 to 5 feet. Grinding used truck linings gave a mean of 3.8 fibers/ml on personal samplers, and beveling new truck linings gave a mean of 37.5 fibers/ml. In brake-drum dust, a mean of 83% of chrysotile fibers were very short fibrils, and some particles had the features of fosterite, a heat-altered form of chrysotile. Second, the authors examined 104 union vehicle maintenance workers who volunteered, and analyzed 90 with over 10 years' work. Of these 90, 24 (27%) had chest x-ray changes. Of 87 given breathing tests, 57 (66%) had some abnormality. Both x-ray changes and reduced lung capacity were more common after 20 years of work. The authors concluded that the findings suggest asbestos disease will be present among such workers. They called the study preliminary and limited to volunteers, so its results cannot readily be generalized to all US brake workers.

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: Cross-sectional study combining workplace air sampling and electron microscopy of brake-drum dust with a preliminary clinical survey (history, examination, chest x-ray, breathing tests) of volunteer workers
• Who was studied: 104 male volunteers from a union of vehicular maintenance workers in New York City. After exclusions (3 with under 10 years in a shop, 9 with possible other asbestos exposure, 2 with known chest disease), 90 were analyzed: 84 still working and 6 retired because of age. 67 were general mechanics, and 61 of them did brake lining more than once a week for ten years or more. The workers' mean age was 48 ± 12 years, with 28 ± 8 years on the job.
• Exposure: Chrysotile asbestos from brake linings, released during brake maintenance on automobiles and trucks: blowing dust from drum brakes, renewing used linings by grinding, and beveling new linings. Peak personal and background air samples were taken.
• Main results:
  • Blowing dust out of automobile drum brakes: personal sample values varied widely, and those taken at 3-5 feet were the highest, with a mean of 15.9 fibers/ml (fibers longer than 5 microns).
  • Renewing used truck brake linings by grinding: the mean personal sample concentration was 3.8 fibers/ml.
  • Beveling new truck linings: the mean concentration was 37.5 fibers/ml.
  • The authors reported that peak values frequently exceeded the 10 fiber/ml US legal limit for peak values.
  • In ten bulk samples of brake-drum dust examined by electron microscopy, a mean of 83% of chrysotile fibers were short fibrils. In their summary, the authors describe over four-fifths of the chrysotile fibers as below 0.4 micron in length and not visible by optical microscopy.
  • Chrysotile made up a mean of about 20% of the total mass of the ten bulk brake-drum dust samples.
  • A majority of fibers in brake-drum dust showed little alteration from typical chrysotile.
  • Some particles had the structural and chemical characteristics of fosterite, a thermal alteration product of chrysotile.
  • Among 90 workers with over 10 years' experience, 24 (27%) had x-ray changes: 18 (20%) parenchymal fibrosis, 5 (6%) pleural thickening or calcification, and 1 (1%) both. The x-ray changes consistent with asbestosis increased with time since the start of work, and this trend was statistically significant.
  • Among 87 workers with over 10 years' experience given breathing tests, 14 (16%) had restrictive, 32 (37%) obstructive and 11 (13%) combined patterns, for 57 (66%) with any abnormality.
  • Decreased vital capacity became more common with age, most markedly after 20 years from the start of auto work. The authors reported these differences as statistically significant, with p between .05 and .02.
  • The authors reported that both chest x-ray changes and restrictive breathing-test results were significantly more common after 20 years of exposure than before.
  • Smokers and ex-smokers were significantly more often obstructed than non-smokers. Smoking groups did not differ significantly in restriction.
  • No significant association was found between restriction on breathing tests and abnormal x-rays. Findings on physical examination of the lungs were minimal: five cases of clubbing and four instances of fine rales.
• The authors' conclusion: The authors concluded that both time-weighted average and peak levels showed significant asbestos exposure. They said the findings suggest asbestos disease will be present among brake maintenance workers, and that appropriate control measures should be urgently instituted.
• Limitations the authors state:
  • The authors described the study as preliminary, limited in scope and restricted to volunteers, so its results cannot readily be generalized to all US brake maintenance workers.
  • The biologic activity of the altered chrysotile materials in brake dust had not been studied.
  • The authors called the correlations between optical fiber counts and electron microscopy incomplete.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Chrysotile, Fibril, Chest X-Ray.

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