Exposure to chrysotile asbestos associated with unpacking and repacking boxes of automobile brake pads and shoes

Our plain-English summary of Exposure to chrysotile asbestos associated with unpacking and repacking boxes of automobile brake pads and shoes, by A.K. Madl, L.L. Scott, D.M. Murbach, et al (The Annals of Occupational Hygiene, 2008).

The study

• Authors: A.K. Madl, L.L. Scott, D.M. Murbach, K.A. Fehling, B.L. Finley, D.J. Paustenbach
• Journal: The Annals of Occupational Hygiene
• Published: 2008;52(6):463-79
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Industrial hygiene surveys and epidemiologic studies of auto mechanics have shown that these workers are not at an increased risk of asbestos-related disease; however, concerns continue to be raised regarding asbestos exposure from asbestos-containing brakes. Handling new asbestos-containing brake components has recently been suggested as a potential source of asbestos exposure. A simulation study involving the unpacking and repacking of 105 boxes of brakes (for vehicles ca. 1946-80), including 62 boxes of brake pads and 43 boxes of brake shoes, was conducted to examine how this activity might contribute to both short-term and 8-h time-weighted average exposures to asbestos. Breathing zone samples on the lapel of a volunteer worker (n = 80) and area samples at bystander (e.g., 1.5 m from worker) (n = 56), remote area (n = 26) and ambient (n = 10) locations collected during the unpacking and repacking of boxes of asbestos-containing brakes were analyzed by phase contrast microscopy and transmission electron microscopy. Exposure to airborne asbestos was characterized for a variety of parameters including the number of boxes handled, brake type (i.e. pads versus shoes) and the distance from the activity (i.e. worker, bystander and remote area). This study also evaluated the fiber size and morphology distribution according to the International Organization for Standardization analytical method for asbestos. It was observed that (i) airborne asbestos concentrations increased with the number of boxes unpacked and repacked, (ii) handling boxes of brake pads resulted in higher worker asbestos exposures compared to handling boxes of brake shoes, (iii) cleanup and clothes-handling tasks produced less airborne asbestos than handling boxes of brakes and (iv) fiber size and morphology analysis showed that while the majority of fibers were free (e.g. not associated with a cluster or matrix), <30% were respirable and even fewer were of the size range (>20 microm length) considered to pose the greatest risk of asbestos-related disease. It was found that average airborne chrysotile concentrations (30 min) ranged from 0.086 to 0.368 and 0.021 to 0.126 f cc(-1) for a worker unpacking and repacking 4-20 boxes of brake pads and 4-20 boxes of brake shoes, respectively. Additionally, average airborne asbestos exposures (30 min) at bystander locations ranged from 0.004 to 0.035 and 0.002 to 0.011 f cc(-1) when 4-20 boxes of brake pads and 4-20 boxes of brake shoes were handled, respectively. These data show that a worker handling a relatively large number of boxes of brakes over short periods of time will not be exposed to airborne asbestos in excess of its historical or current short-term occupational exposure limits.

In plain English

This was a simulation study in a closed automobile repair shop in Santa Rosa, California. One volunteer unpacked and repacked 105 boxes of old replacement brakes, 62 of pads and 43 of shoes. The brake material contained chrysotile asbestos, and no amphibole asbestos was found. Air was sampled on the worker's lapel, at bystander spots 1.5 m away, farther across the shop, and outdoors. Over 30 minutes, the worker's average airborne asbestos ranged from 0.086 to 0.368 fibers per cubic centimeter of air (f/cc) for 4 to 20 boxes of pads, and from 0.021 to 0.126 f/cc for the same numbers of boxes of shoes. Bystander averages were 0.004 to 0.035 and 0.002 to 0.011 f/cc. Levels generally rose with the number of boxes handled, and pad boxes gave the worker two to seven times higher levels than shoe boxes. Cleanup and clothes handling gave lower worker levels. The authors concluded that short-term levels for the worker and bystander were below the current OSHA excursion limit and all previous US occupational asbestos standards.

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 (exposure assessment) study with personal and area air sampling
• Who was studied: One volunteer worker handling 105 boxes of vintage replacement brakes (62 boxes of pads, 43 boxes of shoes) in an automobile repair shop in Santa Rosa, California. Testing took place on 27 July 2004 (Phase I) and on 5 and 6 November 2005 (Phase II). Air samples were taken at the worker, bystander, remote and outdoor locations.
• Exposure: Chrysotile asbestos in new, unused brake pads and shoes made before the mid-1970s. Individual bulk measurements ranged from 3 to 60% chrysotile, and no amphibole asbestos was detected. The tasks were unpacking and repacking boxes (2 to 36 boxes per event), cleaning up counter dust, and shaking and folding worn coveralls.
• Main results:
  • Worker (lapel), 30-minute averages: 0.086 to 0.368 f/cc for 4 to 20 boxes of brake pads, and 0.021 to 0.126 f/cc for the same numbers of boxes of brake shoes.
  • Bystander locations (1.5 m away), for the same numbers of boxes: average 0.004 to 0.035 f/cc for brake pads and 0.002 to 0.011 f/cc for brake shoes.
  • Airborne asbestos concentrations generally increased with the number of boxes handled.
  • For the worker, boxes of brake pads produced two to seven times higher airborne asbestos concentrations than boxes of brake shoes over 15 or 30 minutes.
  • Cleanup of countertop dust and handling of worn clothes gave 0.004 and 0.011 f/cc for the worker, and 0.002 and 0.010 f/cc at bystander locations, respectively.
  • The estimated 8-hour time-weighted average for a worker handling up to 40 boxes of brakes in a workday was 0.063 f/cc.
  • In worker samples, assuming only fibers thinner than 0.7 micrometers reach the deep lung, only 30% of the total fibers were respirable.
  • 0 to 7% of the total fibers counted were both respirable and longer than 20 micrometers.
• The authors' conclusion: The authors concluded that short-term airborne asbestos concentrations for a worker unpacking and repacking boxes of asbestos-containing brakes, and for a bystander nearby, were below the current OSHA excursion limit and all previous US occupational asbestos standards.
• Limitations the authors state:
  • The authors stated that keeping the shop closed likely produced higher worker and bystander exposures than a fully ventilated facility would have.
  • The authors stated that some conditions, such as low ventilation and many boxes handled in a short time, may represent more of a worst-case scenario.
  • Low-concentration asbestos counts are generally not normally distributed, so the authors did not attempt statistical comparisons.
  • Fewer fibers were counted in area samples than in personal samples, so the authors expected wider uncertainty for area concentrations.

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, Brake Lining, Industrial Hygiene, Asbestos Exposure, Work Practice Simulation, Time-Weighted Average (TWA), Personal Breathing Zone Sample, phase contrast microscopy (PCM).

Related studies

• A study of airborne chrysotile concentrations associated with handling, unpacking, and repacking boxes of automobile clutch discs — G.C. Jiang, A.K. Madl, et al. (2008)
• Reduction of the biological potential of chrysotile asbestos arising from conditions of service on brake pads — A.M. Langer (2003)
• 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)
• Environmental and occupational health hazards associated with the presence of asbestos in brake linings and pads (1900 to present): a "state-of-the-art" review — D.J. Paustenbach, B.L. Finley, et al. (2004)
• 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)
• 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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