An exposure study of bystanders and workers during the installation and removal of asbestos gaskets and packing

Our plain-English summary of An exposure study of bystanders and workers during the installation and removal of asbestos gaskets and packing, by C. Mangold, K. Clark, A. Madl, et al (Journal of Occupational and Environmental Hygiene, 2006).

The study

• Authors: C. Mangold, K. Clark, A. Madl, D. Paustenbach
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2006;3(2):87-98
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

From 1982 until 1991, a series of studies was performed to evaluate the airborne concentration of chrysotile asbestos associated with replacing gaskets and packing materials. These studies were conducted by the senior author in response to concerns raised by a report from the Navy in 1978 on asbestos exposures associated with gasket work. A series of studies was conducted because results of those who worked with gaskets within the Navy study did not address the background concentrations of asbestos in the work areas, which may have been significant due to the presence of asbestos insulation in the ships and shipyards. The intent of the studies performed from 1982 through 1991 was to re-create the Navy's work practices in a contaminant-free environment during an 8-hour workday (so the data could be compared with the OSHA permissible exposure limit [PEL]). Samples were collected to characterize personal and area airborne asbestos concentrations associated with the formation, removal, and storage of gaskets, as well as the scraping of flanges and the replacement of valve packing. The results indicate that the 8-hour time-weighted average (TWA) exposures of pipefitters and other tradesmen who performed these activities were below the current PEL and all previous PELs. Specifically, the highest average 8-hour TWA concentration measured for workers manipulating asbestos gaskets during this study was 0.030 f/cc (during gasket removal and flange face scraping onboard a naval ship). Likewise, the 8-hour TWA breathing zone concentrations of a worker removing and replacing asbestos valve packing did not exceed 0.016 f/cc. In most cases, the concentrations were not distinguishable from ambient levels of asbestos in the ships or the general environment. These results are not surprising given that asbestos fibers in gasket materials are encapsulated within a binder.

In plain English

This article reported a series of air-sampling tests carried out between 1982 and 1991 by the first author. The tests measured airborne asbestos while workers formed, removed and installed gaskets and replaced valve packing that the authors described as containing chrysotile asbestos. Most tests were done in cleaned enclosures or buildings to exclude other asbestos sources. One 1982 test was done in industrial work areas that had background asbestos. In the cleaned settings, average 8-hour breathing zone levels ranged from at or below detection limits up to 0.030 f/cc. The highest level was during gasket removal with flange scraping on board the naval ship USS Gypsy. In the uncleaned work areas, levels during gasket work (0.02 to 0.14 f/cc) were not statistically different from background (0.02 to 0.11 f/cc). Personal samples during packing work covered about 4.5 hours. The authors concluded that exposures were below current and historical OSHA limits and suggested that health risks were negligible. They noted that bulk analysis was missing for many materials. The work was funded by Garlock, a gasket maker involved in asbestos litigation, and two authors have testified as experts in asbestos cases.

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: Series of five air-sampling exposure studies (Tests I to V) combining simulation and worksite elements
• Who was studied: A mechanic, workers, the first author and an assistant performing gasket and packing tasks between 1982 and 1991, in cleaned enclosures and buildings, industrial work areas, and on board the USS Gypsy. Gaskets and valves came from former naval ships and a municipal steam plant.
• Exposure: Chrysotile asbestos gaskets and valve packing. Activities were scribing, cutting and punching gasket material, opening flanges, removing gaskets, cleaning flange faces with a putty knife, scraper or wire brushes, and removing and installing valve packing. Bulk analysis in the 1989 test found 60-80% chrysotile in removed gaskets and 70-80% in installed gaskets.
• Main results:
  • Test I (1982, enclosure, no flange face cleaning): average breathing zone 8-hour TWAs were 0.004 to 0.005 f/cc across three gasket types.
  • Test II (1982, uncleaned industrial work areas): 8-hour TWA exposures during gasket work, including background, were 0.02 to 0.14 f/cc. Background area samples averaged 0.02 to 0.11 f/cc.
  • Test II: there was no statistically significant difference between background and pooled activity measurements (p = 0.073).
  • Test III (1983): the 20 breathing zone samples during gasket removal and flange scraping on board the USS Gypsy averaged 0.030 f/cc (standard deviation 0.021 f/cc). The 10 samples at the onshore site averaged 0.023 f/cc.
  • Test IV (1989): average breathing zone concentrations during gasket formation with hand tools were at or below the detection limit of 0.005 f/cc by PCM.
  • Test IV: worker breathing zone 8-hour TWAs were 0.007 f/cc for hand wire brushing and 0.009 f/cc for power wire brushing (PCM). Area samples for the same tasks averaged 0.024 and 0.028 f/cc by TEM, and 0.003 and 0.001 f/cc by PCM.
  • Test V (1991, valve packing, about 4.5 hours of personal sampling): the operator was below the detection limit of 0.011 f/cc and the bystander below 0.009 f/cc. A blind recount gave 0.016 f/cc for the worker and 0.009 f/cc for the bystander. The eight area samples averaged 0.008 f/cc by TEM and 0.004 f/cc by PCM.
• The authors' conclusion: The authors concluded that exposures of workers removing and installing asbestos gaskets and packing were below historical and current occupational exposure limits, and that the data suggest negligible health risks from these activities.
• Limitations the authors state:
  • Bulk sampling data were lacking for many of the gaskets and packing handled, so asbestos content was assumed for those materials based on the first author's experience.
  • Direct comparison with other gasket and packing studies is difficult because of differences in tasks, sampling and analytical methods, and study design.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Gasket, Chrysotile, Asbestos Exposure, Permissible Exposure Limit (PEL), Asbestos Packing, Time-Weighted Average (TWA), Pipefitter.

Related studies

• Exposure to airborne asbestos during removal and installation of gaskets and packings: a review of published and unpublished studies — A.K. Madl, K. Clark, et al. (2007)
• Fiber release during the removal of asbestos-containing gaskets: a work practice simulation — W.E. Longo, W.B. Egeland, et al. (2002)
• Measured removal rates of chrysotile asbestos fibers from air and comparison with theoretical estimates based on gravitational settling and dilution ventilation — J. Sahmel, H.J. Avens, et al. (2015)
• 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)
• Airborne asbestos exposures associated with gasket and packing replacement: a simulation study of flange and valve repair work and an assessment of exposure variables — A.K. Madl, K.D. Devlin, et al. (2015)
• Exposure data from multi-application, multi-industry maintenance of surfaces and joints sealed with asbestos-containing gaskets and packing — F. Boelter, C. Simmons, et al. (2011)

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