Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability

Our plain-English summary of Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability, by M.A. Atkinson, M. O'sullivan, S. Zuber, et al (American Journal of Industrial Medicine, 2004).

The study

• Authors: M.A. Atkinson, M. O'sullivan, S. Zuber, R.F. Dodson
• Journal: American Journal of Industrial Medicine
• Published: 2004;46(6):545-53
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Chrysotile asbestos has found multiple applications in the production of friction products. At one point it comprised 40-50% of the composition of brake linings thus generating the potential for the development of asbestos related diseases in millions of workers involved in vehicle repairs. While some attention has been given to the health status of workers involved in the handling of worn components, little has been given to the potential for exposure during the handling and fitting of new (unused) components as replacement parts.

Methods: Unused brake linings or brake shoes with attached linings from four different sources were gently rinsed with prefiltered water that was then collected on filters for analysis by Analytical Transmission Electron Microscope.

Results: Large numbers of chrysotile asbestos containing structures, the majority of respirable size, were present in each sample.

Conclusions: We conclude that any manipulation of new asbestos containing brake components would be expected to yield free dust containing chrysotile asbestos of respirable size. That the vast majority of these fibers and particulates would not be counted as regulated fibers rendering assessment of potential exposures in the work place, based on data of Permissible Exposure Limits or Regulated Fibers, questionable.

In plain English

This laboratory study asked whether loose dust could be collected from new brake parts containing chrysotile asbestos. The authors gently rinsed four samples with filtered water, each of two components: three pairs of unused drum brake linings predrilled for rivets, and one pair of unused brake shoes with attached linings. Particles in the rinse water were examined with an analytical transmission electron microscope, and 150 structures were measured from each sample. Asbestos structures made up 76.1% of particles in sample 1, 62.7% in sample 3, 50.7% in sample 2 and 44.7% in sample 4. Judged by size alone, all single chrysotile fibrils and 88.5% to 98.5% of fiber bundles were classed as potentially respirable. Under the light-microscopy counting rules used for workplace limits, none of the fibrils and only 23.5% to 44.2% of the bundles would have been counted. The attached-lining brake shoes gave the lowest asbestos proportion, which the authors suggested supports the idea that drilling frees more dust. The authors concluded that any handling of new asbestos-containing brake parts would be expected to release chrysotile dust of respirable size.

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: Laboratory analysis of dust rinsed from the surfaces of unused brake components, examined by analytical transmission electron microscopy
• Who was studied: Four samples of unused brake components from four different sources, each made up of two components (eight in total): two unused drum-brake linings predrilled for rivets identified as A GM 597804 80 (sample 1), two linings identified as B-50-Marshall (sample 2), two linings identified as Inlite-2006A 292A (sample 3), and two unused brake shoes with attached linings identified as Bendix MGFF (sample 4). 150 structures were measured per sample.
• Exposure: Chrysotile asbestos in free dust on the surface of unused brake linings and shoes. Representative structures were confirmed as chrysotile by X-ray energy dispersive analysis and selected area diffraction. No grinding, drilling or other handling was tested.
• Main results:
  • Asbestos structures (fibrils, bundles and clusters) as a percentage of all particles: 76.1% in sample 1, 62.7% in sample 3, 50.7% in sample 2 and 44.7% in sample 4
  • By the study's size criteria, 100% of fibrils in all four samples were potentially respirable
  • Bundles classed as potentially respirable: 98.5% in sample 1, 98% in sample 2, 96.2% in sample 3 and 88.5% in sample 4
  • Fibrils and bundles combined across all four samples: 92.8% were respirable, ranging from 89.3% in sample 4 to 94.7% in samples 1 and 3
  • Non-fibrous matrix particles classed as respirable ranged from 97.2% in sample 3 to 88.2% in sample 2
  • Matrix particles with protruding bundles or fibrils ('matrix plus') classed as respirable ranged from 82.6% in sample 2 to 66.7% in sample 4
  • Applying the light-microscopy (NIOSH) counting criteria for regulated fibers, none of the fibrils in any sample would have been detected
  • Under the same counting criteria, only 44.2% of bundles in sample 4, 32.7% in sample 3, 24.6% in sample 1 and 23.5% in sample 2 would have been counted
  • The lowest proportion of asbestos-containing particles came from sample 4, the brake shoes with linings already mounted. The other samples were unmounted and predrilled, which the authors said supports the contention that drilling would increase freed dust.
• The authors' conclusion: The authors concluded that any manipulation of new asbestos-containing brake components would be expected to yield free dust containing chrysotile asbestos of respirable size. They also said that, because most of these fibers and particles would not be counted as regulated fibers, workplace exposure assessments based on Permissible Exposure Limits or regulated fibers are questionable.

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, Friction Products, Brake Lining, Permissible Exposure Limit (PEL).

Related studies

• 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)
• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)
• Airborne asbestos concentration from brake changing does not exceed permissible exposure limit — C.L. Blake, D.R. Van Orden, et al. (2003)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)
• Evaluation of asbestos exposure during brake repair and replacement — H. Kakooei, M. Hormozy, et al. (2011)
• 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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