Chrysotile asbestos exposure associated with removal of automobile exhaust systems (ca. 1945-1975) by mechanics: results of a simulation study

Our plain-English summary of Chrysotile asbestos exposure associated with removal of automobile exhaust systems (ca. 1945-1975) by mechanics: results of a simulation study, by D.J. Paustenbach, A.K. Madl, E. Donovan, et al (Journal of Exposure Science & Environmental Epidemiology, 2006).

The study

• Authors: D.J. Paustenbach, A.K. Madl, E. Donovan, K. Clark, K. Fehling, T.C. Lee
• Journal: Journal of Exposure Science & Environmental Epidemiology
• Published: 2006;16(2):156-71
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

For decades, asbestos-containing gaskets were used in virtually every system that involved the transport of fluids or gases. Prior to the mid-1970s, some automobile exhaust systems contained asbestos gaskets either at flanges along the exhaust pipes or at the exhaust manifolds of the engine. A limited number of automobile mufflers were lined with asbestos paper. This paper describes a simulation study that characterized personal and bystander exposures to asbestos during the removal of automobile exhaust systems (ca. 1945-1975) containing asbestos gaskets. A total of 16 pre-1974 vehicles with old or original exhaust systems were studied. Of the 16 vehicles, 12 contained asbestos gaskets in the exhaust system and two vehicles had asbestos lining inside the muffler. A total of 82 samples (23 personal, 38 bystander, and 21 indoor background) were analyzed by Phase Contrast Microscopy (PCM) and 88 samples (25 personal, 41 bystander, and 22 indoor background) by Transmission Electron Microscopy (TEM). Only seven of 25 worker samples analyzed by TEM detected asbestos fibers and 18 were below the analytical sensitivity limit (mean 0.013 f/cc, range 0.001-0.074 f/cc). Applying the ratio of asbestos fibers:total fibers (including non-asbestos) as determined by TEM to the PCM results showed an average (1 h) adjusted PCM worker exposure of 0.018 f/cc (0.002-0.04 f/cc). The average (1 h) adjusted PCM airborne concentration for bystanders was 0.008 f/cc (range 0.0008-0.015 f/cc). Assuming a mechanic can replace four automobile single exhaust systems in 1 workday, the estimated 8-h time-weighted average (TWA) for a mechanic performing this work was 0.01 f/cc. Under a scenario where a mechanic might repeatedly conduct exhaust work, these results suggest that exposures to asbestos from work with automobile exhaust systems during the 1950s through the 1970s containing asbestos gaskets were substantially below 0.1 f/cc, the current PEL for chrysotile asbestos, and quite often were not detectable.

In plain English

This simulation study measured airborne asbestos as old automobile exhaust systems were removed. Two mechanics at a Santa Rosa, California, muffler shop worked on 16 pre-1974 vehicles. Tests found asbestos gaskets in 12 and asbestos-paper muffler linings in two. The gaskets contained 9.5% to 80.1% chrysotile; no amphibole asbestos was found. Air was sampled on the mechanic's lapel, at bystander stations about 4 feet from the car (one 23 inches), and at the shop's ends. Of 25 mechanic samples analyzed by electron microscopy (TEM), 18 were below detection; seven contained asbestos. In the seven mechanic and six bystander samples with TEM-confirmed asbestos, adjusted light-microscope counts averaged 0.018 and 0.008 f/cc during the work. Assuming four single exhaust jobs daily, the authors assigned removal exposure to each job's first hour and shop background (0.0014 f/cc) to the other hours, estimating an 8-hour mechanic average of 0.01 f/cc. Other estimates were 0.006 f/cc for mechanics on dual systems, and 0.005 (single) and 0.003 f/cc (dual) for bystanders. The authors concluded exposures were substantially below the current 0.1 f/cc chrysotile limit. They noted that many results below detection made statistical comparisons difficult.

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 exhaust system removal
• Who was studied: 16 pre-1974 vehicles worked on by two mechanics at a muffler shop in Santa Rosa, California, in January and July 2004; personal (mechanic), bystander and background air samples
• Exposure: chrysotile in exhaust pipe and manifold gaskets (9.5% to 80.1% by XRD) and in asbestos-paper muffler linings (28.3% to 41.7%); no amphibole asbestos found by PLM
• Main results:
  • Bulk analysis showed 12 of the 16 vehicles had asbestos gaskets in the exhaust system and two had mufflers lined with asbestos paper
  • Bystander samples were taken at four stations approximately 4 feet from the vehicle, except one station placed 23 inches from the rear of each vehicle because of limited space
  • Mechanics: of 25 personal samples analyzed by TEM, 18 were below the analytical sensitivity limit and only seven were confirmed to contain asbestos; TEM concentrations ranged from 0.0005 to 0.105 f/cc, average 0.013 f/cc
  • Average PCM concentrations adjusted for asbestos content, calculated only from samples in which TEM detected asbestos, during the work: 0.018 f/cc for mechanics (n=7), 0.008 f/cc for bystanders (n=6), and 0.003 f/cc for indoor background (n=2)
  • Bystanders: only six of 41 TEM samples were above the sensitivity limit and confirmed to contain asbestos
  • For the 8-hour estimates, the authors assigned gasket and muffler removal exposure to the first hour of each job and applied shop remote-background concentrations (0.0014 f/cc in their calculation) to non-gasket work
  • Estimated 8-hour time-weighted average for mechanics, assuming four single exhaust jobs per day: 0.01 f/cc; for dual exhaust systems (two cars per day): 0.006 f/cc
  • Estimated 8-hour time-weighted averages for bystanders: 0.005 f/cc (single systems, four cars per day) and 0.003 f/cc (dual systems, two cars per day)
  • Indoor concentrations elsewhere in the shop during the work were similar to those measured before the study; the single adjusted indoor background sample taken before any work was 0.022 f/cc, which the authors said seemed high
• The authors' conclusion: The authors concluded that estimated 8-hour exposures for mechanics and bystanders were substantially below 0.1 f/cc, the current limit for chrysotile, and below all previous US occupational standards
• Limitations the authors state:
  • Because so many samples were below the analytical sensitivity limit, statistical comparison of mechanic, bystander and background levels was difficult
  • Comparisons of indoor background before and during the work were not conclusive, given the many non-detects and only five pre-work samples
  • 12 samples were overloaded with particulate and could not be analyzed

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, Asbestos Exposure, Work Practice Simulation, Gasket, Bystander Exposure, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Analytical Sensitivity.

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