Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets

Our plain-English summary of Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets, by C.L. Blake, G.S. Dotson, R.D. Harbison (Regulatory Toxicology and Pharmacology, 2006).

The study

• Authors: C.L. Blake, G.S. Dotson, R.D. Harbison
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2006;45(2):214-22
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Five test sessions were conducted to assess asbestos exposure during the removal or installation of asbestos-containing gaskets on vehicles. All testing took place within an operative automotive repair facility involving passenger cars and a pickup truck ranging in vintage from late 1960s through 1970s. A professional mechanic performed all shop work including engine disassembly and reassembly, gasket manipulation and parts cleaning. Bulk sample analysis of removed gaskets through polarized light microscopy (PLM) revealed asbestos fiber concentrations ranging between 0 and 75%. Personal and area air samples were collected and analyzed using National Institute of Occupational Safety Health (NIOSH) methods 7400 [phase contrast microscopy (PCM)] and 7402 [transmission electron microscopy (TEM)]. Among all air samples collected, approximately 21% (n = 11) contained chrysotile fibers. The mean PCM and phase contrast microscopy equivalent (PCME) 8-h time weighted average (TWA) concentrations for these samples were 0.0031 fibers/cubic centimeters (f/cc) and 0.0017 f/cc, respectively. Based on these findings, automobile mechanics who worked with asbestos-containing gaskets may have been exposed to concentrations of airborne asbestos concentrations approximately 100 times lower than the current Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit (PEL) of 0.1 f/cc.

In plain English

The authors measured airborne asbestos in a working Detroit, Michigan, automobile garage. In five sessions without ventilation, a professional mechanic removed old gaskets or installed new asbestos-containing ones on a 1974 Chevrolet Malibu, 1978 Chevrolet pickup and Ford 390 V-8 engine. The nine removed gaskets contained 0 to 75% asbestos, with chrysotile in six. About 21% of air samples (11) contained chrysotile; none contained amphibole fibers. Results were reported as 8-hour time-weighted averages, counting unsampled time as zero. Phase contrast microscopy counts, which include non-asbestos fibers, averaged 0.0015 f/cc for all 53 samples and 0.0031 f/cc for the 11 asbestos-containing ones; their asbestos-specific average was 0.0017 f/cc. The mechanic's personal fiber counts ranged from 0.001 to 0.0079 f/cc; only 3 of 10 contained chrysotile, the highest asbestos-specific value being 0.0044 f/cc. The authors reported no asbestos during new-gasket installation, though one table lists an asbestos-containing Malibu installation sample. The authors concluded that standard work practices released limited fibers and gave minimal exposure. They noted that counting methods exclude short and thin fibers, and a water bath may have reduced fiber release.

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: Exposure assessment: air sampling during five test sessions of gasket removal and installation in a functioning automobile service facility
• Who was studied: One professional (ASE-certified) mechanic working in a two-bay garage in Detroit, Michigan, on a 1974 Chevrolet Malibu, a 1978 Chevrolet pickup truck and a Ford 390 V-8 engine. 10 personal and 43 area air samples were taken.
• Exposure: Removal of old gaskets, which involved scraping, power wire brushing, solvent spray, water-bath washing and sweeping. Installation of new asbestos-containing gaskets. Bulk analysis found chrysotile in the gaskets. Ventilation was shut down and doors were closed during testing.
• Main results:
  • Reported concentrations are 8-hour time-weighted averages calculated by the OSHA formula. Zero was assigned to the part of the 8 hours with no work or sampling; the sessions themselves lasted 122 to 157 minutes.
  • About 21% (11 of all air samples) contained chrysotile fibers by TEM analysis.
  • Average PCM fiber concentration (8-hour TWA) was 0.0015 f/cc for all air samples (n=53) and 0.0031 f/cc for the 11 samples found by TEM to contain asbestos. PCM counts all fibers of qualifying size, asbestos or not.
  • For the 11 asbestos-containing samples, the asbestos-specific (PCME) mean 8-hour TWA was 0.0017 f/cc.
  • Personal samples on the mechanic had PCM (total fiber) 8-hour TWA concentrations from 0.001 to 0.0079 f/cc. Only 3 of the 10 personal samples contained chrysotile, and the highest personal PCME was 0.0044 f/cc.
  • All 43 area samples were reported as approximately 100 times lower than the OSHA PEL of 0.1 f/cc.
  • Background fiber levels ranged from 0.0005 to 0.0015 f/cc (8-hour TWA).
  • The text reports no asbestos fibers in samples collected during installation of new asbestos gaskets. However, Table 7 lists an asbestos-containing area sample (asbestos fiber ratio 0.4) labeled as collected during Chevrolet Malibu gasket installation.
  • No amphibole fibers were identified in any air sample.
  • Of nine removed gaskets, asbestos content ranged from 0 to 75%. Chrysotile was present in six, and no amphibole asbestos was found.
• The authors' conclusion: The authors concluded that airborne asbestos during removal and replacement of asbestos-containing automotive gaskets stayed well below the OSHA limit. In their view, standard work practices produced limited fiber release and only minimal exposure for workers.
• Limitations the authors state:
  • PCM analysis cannot tell asbestos fibers from non-asbestos fibers.
  • The NIOSH counting methods exclude short and long-but-thin asbestos fibers. The authors acknowledged this criticism but argued that such fibers are of less significance.
  • The water bath cleaner may have suppressed fiber release. The authors judged this effect minimal.
  • Fiber loading on filters was below the level NIOSH recommends for accurate counting.
  • Samples at the detection limit were counted at full value, which the authors say exaggerates the mean.

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: Asbestos Exposure, Gasket, Bulk Sample Analysis, Polarized Light Microscopy (PLM), NIOSH, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Chrysotile.

Related studies

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• Airborne asbestos concentration from brake changing does not exceed permissible exposure limit — C.L. Blake, D.R. Van Orden, et al. (2003)
• 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)
• 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)
• 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)
• Chrysotile asbestos exposure associated with removal of automobile exhaust systems (ca. 1945-1975) by mechanics: results of a simulation study — D.J. Paustenbach, A.K. Madl, et al. (2006)

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