An evaluation of short-term exposures of brake mechanics to asbestos during automotive and truck brake cleaning and machining activities

Our plain-English summary of An evaluation of short-term exposures of brake mechanics to asbestos during automotive and truck brake cleaning and machining activities, by R.O. Richter, B.L. Finley, D.J. Paustenbach, et al (Journal of Exposure Science & Environmental Epidemiology, 2009).

The study

• Authors: R.O. Richter, B.L. Finley, D.J. Paustenbach, P.R. Williams, P.J. Sheehan
• Journal: Journal of Exposure Science & Environmental Epidemiology
• Published: 2009;19(5):458-74
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Historically, the greatest contributions to airborne asbestos concentrations during brake repair work were likely due to specific, short-duration, dust-generating activities. In this paper, the available short-term asbestos air sampling data for mechanics collected during the cleaning and machining of vehicle brakes are evaluated to determine their impact on both short-term and daily exposures. The high degree of variability and lack of transparency for most of the short-term samples limit their use in reconstructing past asbestos exposures for brake mechanics. However, the data are useful in evaluating how reducing short-term, dust-generating activities reduced long-term exposures, especially for auto brake mechanics. Using the short-term dose data for grinding brake linings from these same studies, in combination with existing time-weighted average (TWA) data collected in decades after grinding was commonplace in rebuilding brake shoes, an average 8-h TWA of approximately 0.10 f/cc was estimated for auto brake mechanics that performed arc grinding of linings during automobile brake repair (in the 1960s or earlier). In the 1970s and early 1980s, a decline in machining activities led to a decrease in the 8-h TWA to approximately 0.063 f/cc. Improved cleaning methods in the late 1980s further reduced the 8-h TWA for most brake mechanics to about 0.0021 f/cc. It is noteworthy that when compared with the original OSHA excursion level, only 15 of the more than 300 short-term concentrations for brake mechanics measured during the 1970s and 1980s possibly exceeded the standard. Considering exposure duration, none of the short-term exposures were above the current OSHA excursion level.

In plain English

This paper reviewed previously collected air measurements; it was not a new sampling study. The authors gathered 15 studies (five government reports and ten published studies) from the United States, United Kingdom, Finland, Germany and Hong Kong, conducted between 1968 and 2000. Together these held more than 300 short-term personal air samples taken while mechanics cleaned or machined brakes on cars, light trucks, heavy trucks and buses. For car and light-truck drum brakes, compressed-air blow-out gave the highest mean and maximum concentrations (3.0 and 29 f/cc). For heavy trucks and buses, grinding linings without exhaust controls averaged 56 f/cc, compared with 1.5 f/cc with exhaust, and machine beveling averaged 37 f/cc. The authors added grinding data to 8-hour averages from a 2003 analysis by Paustenbach and colleagues. From this they estimated about 0.10 f/cc for auto mechanics who ground linings (1960s or earlier), against 0.063 f/cc in the 1970s and 0.0021 f/cc in the late 1980s. The authors concluded that short-term exposures were well below the original and current OSHA limits. They also said the highly variable data, which lacked transparency, made it difficult to reconstruct exposures from these samples alone.

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: Review and reanalysis of previously published short-term asbestos air sampling data (government reports and published studies), with calculation of short-term doses and an estimate of past 8-hour time-weighted averages
• Who was studied: Air samples for automobile and truck brake mechanics from 15 studies (5 government reports, 10 published studies) carried out in the United States, United Kingdom, Finland, Germany and Hong Kong between 1968 and 2000. In total, more than 300 short-term personal samples. Cars and light trucks were analysed separately from heavy trucks and buses.
• Exposure: Airborne asbestos in the breathing zone during specific brake cleaning methods (compressed air, dry brush, vacuum, wet brush, damp cloth, water washing) and machining activities (grinding and beveling linings, rivet removal and installation, turning drums and discs). Fibers were counted by phase contrast microscopy. The article does not identify a specific fiber type in the measurements.
• Main results:
  • Cars and light trucks, cleaning of drum brakes (69 samples): compressed-air blow-out had the highest mean (3.0 f/cc) and maximum (29 f/cc) concentrations.
  • Cars and light trucks: mean levels for the other cleaning methods ranged from 0.04 f/cc (vacuum) to 1.6 f/cc (wet brush).
  • Heavy trucks and buses, cleaning of drum brakes (42 samples, seven methods): mean levels ranged from 0.25 f/cc for opening/water washing to 1.9 f/cc for damp cloth wiping.
  • Heavy trucks and buses, grinding of brake linings: the mean without exhaust controls (56 f/cc) was about 40 times the mean with exhaust controls (1.5 f/cc).
  • Heavy trucks and buses, beveling of brake linings: the mean for hand beveling (0.40 f/cc) was almost 100 times lower than for machine beveling (37 f/cc).
  • Auto brake mechanics: adding a grinding dose to the 1970s brake-job average from Paustenbach et al. (2003) gave an estimated brake-job average of about 0.18 f/cc, about 60% higher than without grinding.
  • Auto brake mechanics who performed grinding: estimated average 8-hour TWA of approximately 0.10 f/cc.
  • Auto brake mechanics, figures based on the authors' assumptions and Paustenbach et al. (2003): without grinding, the brake-job and 8-hour averages were 0.11 and 0.063 f/cc.
  • Auto brake mechanics, same basis: with dust control measures such as HEPA vacuuming, the averages were 0.005 f/cc during the brake job and 0.0021 f/cc over 8 hours.
  • Cars and light trucks: of more than 130 personal samples, only five could possibly have exceeded the 1972–1986 OSHA ceiling limit (10 f/cc for 15 minutes) if the exposure had continued for 15 minutes.
  • Trucks and buses: of more than 180 personal samples, only 10 had concentrations that could have exceeded the OSHA ceiling limit.
  • The highest calculated short-term doses were 12.8 f/cc*min for car and light-truck mechanics and 19 f/cc*min for heavy-truck and bus mechanics. The authors compared these with doses of 150 f/cc*min implied by the original excursion limit and 30 f/cc*min implied by the current one.
• The authors' conclusion: The authors concluded that, on the basis of the available literature, short-term exposures for brake mechanics cleaning or machining brakes were well below both the original and the current OSHA standards.
• Limitations the authors state:
  • High variability and lack of transparency in most short-term samples limit their use in reconstructing past exposures.
  • Sampling durations often did not match the actual activity duration.
  • Few samples lasted 15 minutes, which hampered direct comparison with the OSHA ceiling limit.
  • There were very few machining samples for cars and light trucks (four).
  • Because the data are so variable, the reconstruction of past exposures is quite uncertain.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Auto mechanics and brake work.

Medical terms in this study, explained in our Lexicon: Short-Term Exposure, Air Sampling, Asbestos Exposure, Brake Lining, Time-Weighted Average (TWA), OSHA.

Related studies

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