A study of airborne chrysotile concentrations associated with handling, unpacking, and repacking boxes of automobile clutch discs

Our plain-English summary of A study of airborne chrysotile concentrations associated with handling, unpacking, and repacking boxes of automobile clutch discs, by G.C. Jiang, A.K. Madl, K.J. Ingmundson, et al (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: G.C. Jiang, A.K. Madl, K.J. Ingmundson, D.M. Murbach, K.A. Fehling, D.J. Paustenbach, B.L. Finley
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;51(1):87-97
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Although automotive friction products (brakes and manual clutches) historically contained chrysotile asbestos, industrial hygiene surveys and epidemiologic studies of auto mechanics have consistently shown that these workers are not at an increased risk of developing asbestos-related diseases. Airborne asbestos levels during brake repair and brake parts handling have been well-characterized, but the potential exposure to airborne asbestos fibers during the handling of clutch parts has not been examined. In this study, breathing zone samples on the lapel of a volunteer worker (n=100) and area samples at bystander (n=50), remote area (n=25), and ambient (n=9) locations collected during the stacking, unpacking, and repacking of boxes of asbestos-containing clutches, and the subsequent cleanup and clothes handling, were analyzed by phase contrast microscopy (PCM) and transmission electron microscopy (TEM). In addition, fiber morphology and size distribution was evaluated using X-ray diffraction, polarized light microscopy, and ISO analytical methods. It was observed that the (1) airborne asbestos concentrations increased with the number of boxes unpacked and repacked, (2) repetitive stacking of unopened boxes of clutches resulted in higher asbestos concentrations than unpacking and repacking the boxes of clutches, (3) cleanup and clothes handling tasks yielded very low asbestos concentrations. Fiber size and morphology analyses showed that amphibole fibers were not detected in the clutches and that the vast majority (>95%) of the airborne chrysotile fibers were less than 20 microm in length. Applying the ratio of asbestos fibers:total fibers (including non-asbestos) as determined by TEM to the PCM results, it was found that 30-min average airborne chrysotile concentrations (PCM adjusted) were 0.026+/-0.004 f/cc or 0.100+/-0.017 f/cc for a worker unpacking and repacking 1 or 2 boxes of clutches, respectively. The 30-min PCM adjusted average airborne asbestos concentrations at bystander locations ranged from 0.002+/-0.001 f/cc and 0.004+/-0.002 f/cc when 1 or 2 boxes of clutches were handled, respectively. Estimated 8-h TWA asbestos exposures for a worker handling 1 or 2 boxes of clutches over a workday ranged from 0.002 to 0.006 f/cc. The 30-min PCM adjusted average airborne asbestos concentration for a worker continuously stacking unopened boxes of clutches was 0.212+/-0.014 f/cc; the 8-h TWA was 0.013 f/cc. Additionally, 30-min PCM adjusted average airborne asbestos concentrations following cleanup and clothing handling were 0.002+/-0.001 f/cc and 0.002+/-0.002 f/cc, respectively, both resulting in estimated 8-h TWA asbestos exposures of 0.0001 f/cc. The results of this study indicate that the handling, unpacking, and repacking of clutches, and the subsequent cleanup and clothes handling by a worker within a short-term period or over the entire workday, result in exposures below the historical and current short-term and 8-h occupational exposure limits for asbestos.

In plain English

In a January 2007 simulation, one person handled pre-mid-1980s clutch disc boxes in a closed Santa Rosa, California shop without active ventilation. Tasks were stacking unopened boxes, unpacking and repacking one or two boxes (some with the disc cleaned or held overhead), counter cleanup, and shaking and folding overalls. Linings averaged 33.7% chrysotile; no amphibole asbestos was detected. Worker means were microscope counts adjusted to the asbestos share found by electron microscopy. First-15-minute means were 0.051 fibers per cubic centimeter (f/cc) for one box, 0.196 for two and 0.231 for stacking. Second-15-minute levels were far lower for unpacking but 0.194 f/cc for stacking. Bystander samples 5 feet away were below 0.02 f/cc. All 15-minute samples were below OSHA's historical 10 f/cc ceiling; 30-minute averages were below the current 1 f/cc limit. Estimated 8-hour averages, assuming background for the day's remainder, were below the current 0.1 f/cc limit. The authors concluded their findings suggest clutch box handlers are not at increased risk of asbestos-related disease. They noted one person did all tasks and warned against extrapolating beyond what was tested.

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: Simulation study measuring airborne asbestos during clutch box handling tasks performed by a single individual
• Who was studied: 27 boxes of clutch discs (one disc each) obtained from an automotive parts warehouse. They were handled by one individual in an auto repair shop in Santa Rosa, CA, on 3 days in January 2007. The shop had its doors closed and no active ventilation. Measured air exchange rates on the three days were 0.4, 2.0 and 0.3 per hour. Air samples were taken on the worker's lapels and at bystander (5 feet), remote (over 50 feet), background and outdoor ambient locations.
• Exposure: Chrysotile-containing passenger vehicle clutch discs made before the mid-1980s. The tasks were stacking 27 unopened boxes, unpacking and repacking one or two boxes (sometimes with dry wipe, spray cleaner or holding the disc overhead), counter cleanup, and shaking and folding overalls.
• Main results:
  • Clutch linings contained a mean of 33.7% plus or minus 2.0 chrysotile by X-ray diffraction, with a range of 20–52%.
  • Polarized light microscopy (limit of detection 1%) found no amphibole asbestos in any of the clutches.
  • Dust collected from the counter averaged 6.8% plus or minus 2.2 chrysotile, with a range of 1–14%.
  • Worker air levels were reported as PCM-adjusted (PCMadj) concentrations. These are phase contrast microscopy fiber counts multiplied by the ratio of asbestos fibers to total fibers found by transmission electron microscopy on the same filters.
  • Worker, first 15 minutes, unpacking and repacking one box: mean PCMadj levels were 0.051 f/cc with no manipulation, 0.050 f/cc with dry wipe and overhead handling, and 0.046 f/cc with spray clean wipe and overhead handling.
  • Worker, second 15 minutes, for the same one-box tasks: PCMadj means were far lower, at 0.002, 0.005 and 0.001 f/cc.
  • Worker, first 15 minutes, unpacking and repacking two boxes: the mean PCMadj level was 0.196 f/cc, higher than with one box.
  • Worker, repetitive stacking of 27 unopened boxes: this gave the highest mean PCMadj levels in the study, 0.231 f/cc in the first 15 minutes and 0.194 f/cc in the second 15 minutes.
  • Bystander samples (5 feet away) were less than 0.02 f/cc regardless of activity. All remote location samples had zero PCMadj values.
  • Worker lapel samples during cleanup and clothes handling had a maximum PCMadj value of 0.006 f/cc.
  • Every individual 15-minute sample was below the historical OSHA 15-minute ceiling limit of 10 f/cc.
  • The calculated 30-minute averages were below the current OSHA 30-minute limit of 1 f/cc. The calculated 8-hour averages were below the current OSHA 8-hour limit of 0.1 f/cc. For the 8-hour figures, the mean background level was assumed for the remaining 7.5 hours of the workday.
  • Estimated 8-hour averages, assuming background levels for the rest of the day, were 0.0016 f/cc for opening one clutch box, 0.0062 f/cc for unpacking and repacking two boxes, and 0.0133 f/cc for stacking boxes.
  • In worker air samples, 29% of free fibers or bundles were of a width the authors treated as respirable (less than 0.7 micrometers). Only 3% of fibers or bundles longer than 20 micrometers were that thin.
  • None of the personal air samples contained detectable amphibole fibers.
• The authors' conclusion: The authors concluded that short-term and 8-hour exposures from unpacking and repacking asbestos-containing clutch boxes were below current and all previous U.S. occupational limits. They also concluded that their findings suggest people opening, repacking or otherwise handling clutch boxes are not at increased risk of asbestos-related disease. They based this inference on comparing estimated cumulative exposures with their estimates for brake mechanics and with reported no-effect levels.
• Limitations the authors state:
  • One individual performed all tasks, so the influence of worker-to-worker variability is unknown.
  • The authors stated that the results should not be extrapolated beyond what was tested.
  • The authors stated that the measured levels are likely biased high for most settings, because of very low ventilation and because the boxes and clutches were at least 30 years old.

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, Industrial Hygiene, Personal Breathing Zone Sample, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Fiber Morphology, X-Ray Diffraction (XRD).

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• 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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• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)

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