A review of historical exposures to asbestos among skilled craftsmen (1940-2006)

Our plain-English summary of A review of historical exposures to asbestos among skilled craftsmen (1940-2006), by P.R. Williams, A.D. Phelka, D.J. Paustenbach (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2007).

The study

• Authors: P.R. Williams, A.D. Phelka, D.J. Paustenbach
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2007;10(5):319-77
• Type of article: Historical article, Review
• Cited by: 53 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This article provides a review and synthesis of the published and selected unpublished literature on historical asbestos exposures among skilled craftsmen in various nonshipyard and shipyard settings. The specific crafts evaluated were insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers, maintenance workers, and abatement workers. Over 50 documents were identified and summarized. Sufficient information was available to quantitatively characterize historical asbestos exposures for the most highly exposed workers (insulators), even though data were lacking for some job tasks or time periods. Average airborne fiber concentrations collected for the duration of the task and/or the entire work shift were found to range from about 2 to 10 fibers per cubic centimeter (cm3 or cc) during activities performed by insulators in various nonshipyard settings from the late 1960s and early 1970s. Higher exposure levels were observed for this craft during the 1940s to 1950s, when dust counts were converted from millions of particles per cubic foot (mppcf) to units of fibers per cubic centimeter (fibers/cc) using a 1:6 conversion factor. Similar tasks performed in U.S. shipyards yielded average fiber concentrations about two-fold greater, likely due to inadequate ventilation and confined work environments; however, excessively high exposure levels were reported in some British Naval shipyards due to the spraying of asbestos. Improved industrial hygiene practices initiated in the early to mid-1970s were found to reduce average fiber concentrations for insulator tasks approximately two- to five-fold. For most other crafts, average fiber concentrations were found to typically range from <0.01 to 1 fibers/cc (depending on the task or time period), with higher concentrations observed during the use of powered tools, the mixing or sanding of drywall cement, and the cleanup of asbestos insulation or lagging materials. The available evidence suggests that although many historical measurements exceeded the current OSHA 8-h time-weighted average (TWA) permissible exposure limit (PEL) of 0.1 fibers/cc, average fiber concentrations generally did not exceed historical occupational exposure limits in place at the time, except perhaps during ripout activities or the spraying of asbestos in enclosed spaces or onboard ships. Additionally, reported fiber concentrations may not have represented daily or actual human exposures to asbestos, since few samples were collected beyond specific short-term tasks and workers sometimes wore respiratory protective equipment. The available data were not sufficient to determine whether the airborne fiber concentrations represented serpentine or amphibole asbestos fibers, which would have a pronounced impact on the potential health hazards posed by the asbestos. Despite a number of limitations associated with the available air sampling data, the information should provide guidance for reconstructing asbestos exposures for different crafts in specific occupational settings where asbestos was present during the 1940 to 2006 time period.

In plain English

This was a review of more than 50 published and selected unpublished documents giving information or airborne asbestos sampling data on 13 skilled crafts, such as insulators, pipefitters and electricians. No craft-specific measurements were found for masons or millwrights. The data came from shipyard and nonshipyard workplaces from the 1940s onward, and most samples covered short tasks. For nonshipyard insulators in the late 1960s and early 1970s, averages ranged from about 2 to 10 fibers/cc. Similar tasks averaged about twofold higher in U.S. shipyards and 10-fold or more higher in British naval shipyards. Improved industrial hygiene from the early to mid-1970s cut insulator averages about two- to five-fold. Older dust counts suggested higher exposures in the 1940s and 1950s. Most other crafts typically averaged less than 0.01 to 1 fibers/cc. Treating short-term averages as 8-hour averages, 12 of more than 60 insulator data sets exceeded the limit then in force. The authors concluded that, carefully interpreted, the data can characterize historical exposures. They noted the data could not show fiber type, and that respirator use and bystander exposures were poorly documented.

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 synthesis of published and selected unpublished air-sampling literature
• Who was studied: More than 50 publications reporting information or air-sampling data on 13 crafts: insulators, pipefitters, boilermakers, masons, welders, sheet-metal workers, millwrights, electricians, carpenters, painters, laborers, maintenance workers and abatement workers. The crafts worked in nonmanufacturing shipyard and nonshipyard settings, from the 1940s to the present. Most data were from the U.S., with some British, Australian and other data.
• Exposure: Airborne asbestos measured during craft tasks. Before the late 1960s this was measured as dust counts in mppcf, converted at 1 mppcf to 6 fibers/cc; later measurements were fiber counts. The discussion focused on personal breathing-zone samples analyzed by phase-contrast microscopy (PCM). Fiber type (chrysotile vs amphiboles) could not be determined for the measurements.
• Main results:
  • Air-sampling data were not available for all crafts. No studies with sampling data specifically for masons were found.
  • No studies with sampling data specifically for millwrights were found.
  • Insulators in nonshipyard settings in the late 1960s and early 1970s had average fiber concentrations of about 2 to 10 fibers/cc.
  • Similar insulator tasks gave averages about twofold greater in U.S. shipyards and 10-fold greater or more in British naval shipyards.
  • Improved industrial hygiene practices reduced average concentrations for insulator tasks about two- to five-fold.
  • Exposures were likely greater in many instances in the 1940s and 1950s than later.
  • For most other crafts, average concentrations typically ranged from less than 0.01 to 1 fibers/cc, depending on the task or period.
  • In a rough comparison, the authors treated short-term insulator averages as if they were 8-hour averages. On that basis, 12 of more than 60 insulator data sets exceeded the 8-hour exposure limit in place at the time.
• The authors' conclusion: The authors concluded that the available air-sampling data, if carefully examined and interpreted, can be used to characterize historical asbestos exposures for different crafts. They added that insulator data may bracket the exposures of less-exposed crafts.
• Limitations the authors state:
  • Studies often did not say whether samples were personal or area samples, or how long sampling lasted.
  • Converting older dust counts (mppcf) to fibers/cc carried significant uncertainty.
  • PCM cannot tell asbestos fibers from non-asbestos fibers.
  • The fiber type behind the measurements could not be determined.
  • There was not enough sampling data on bystander (secondary) exposures.
  • How often workers wore respirators, and how well the respirators worked, is unknown.
  • The data came mostly from larger workplaces and may be biased toward lower levels than in smaller or less controlled facilities.
  • Some simulation studies were done by authors involved in litigation, and the work practices used in them may have been biased.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Insulator, Pipefitter, Abatement, Fibers per Cubic Centimeter (f/cc), Million Particles per Cubic Foot (mppcf), Industrial Hygiene, OSHA.

Related studies

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• Retrospective exposure assessment of airborne asbestos related to skilled craftsmen at a petroleum refinery in Beaumont, Texas (1940-2006) — P. Williams, D. Paustenbach, et al. (2007)
• Release of asbestos fibers during casting ring liner manipulation — D.R. Davis (1995)
• Asbestos in the air of public buildings: a public health risk? — J. Whysner, V.T. Covello, et al. (1994)
• Personal airborne asbestos exposure levels associated with various types of abatement — J.H. Lange, K.W. Thomulka, et al. (2006)
• Estimates of historical exposures by phase contrast and transmission electron microscopy in North Carolina USA asbestos textile plants — J.M. Dement, D. Myers, et al. (2009)

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