Exposure to airborne asbestos during removal and installation of gaskets and packings: a review of published and unpublished studies

Our plain-English summary of Exposure to airborne asbestos during removal and installation of gaskets and packings: a review of published and unpublished studies, by A.K. Madl, K. Clark, D.J. Paustenbach (Journal of Toxicology and Environmental Health. Part B, Critical Reviews, 2007).

The study

• Authors: A.K. Madl, K. Clark, D.J. Paustenbach
• Journal: Journal of Toxicology and Environmental Health. Part B, Critical Reviews
• Published: 2007;10(4):259-86
• Type of article: Review
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In recent years, questions have been raised about the health risks to persons who have been occupationally exposed to asbestos-containing gaskets and packing materials used in pipes, valves, and machinery (pumps, autos, etc.). Up until the late 1970s, these materials were widely used throughout industrial and maritime operations, refineries, chemical plants, naval ships, and energy plants. Seven simulation studies and four work-site industrial hygiene studies of industrial and maritime settings involving the collection of more than 300 air samples were evaluated to determine the likely airborne fiber concentrations to which a worker may have been exposed while working with encapsulated asbestos-containing gaskets and packing materials. Each study was evaluated for the representativeness of work practices, analytical methods, sample size, and potential for asbestos contamination (e.g., insulation on valves or pipes used in the study). Specific activities evaluated included the removal and installation of gaskets and packings, flange cleaning, and gasket formation. In all but one of the studies relating to the replacement of gaskets and packing using hand-held tools, the short-term average exposures were less than the current 30-min OSHA excursion limit of 1 fiber per cubic centimeter (f/cc) and all of the long-term average exposures were less than the current 8-h permissible exposure limit time-weighted average (PEL-TWA) of 0.1 f/cc. The weight of evidence indicates that the use of hand tools and hand-operated power tools to remove or install gaskets or packing as performed by pipefitters or other tradesmen in nearly all plausible situations would not have produced airborne concentrations in excess of contemporaneous regulatory levels.

In plain English

This review covered published and selected unpublished studies of airborne fibers from forming, removing or installing asbestos gaskets and packing in industrial and maritime settings. It analyzed seven simulation and four work-site studies (more than 300 air samples). Bulk samples in the simulation studies contained chrysotile, not amphibole, fibers. In all but one hand-tool replacement study, short-term averages were below the current 30-minute OSHA excursion limit of 1 f/cc. The authors' short-term estimates were about 0.1 f/cc for hand-tool gasket formation, 0.44 f/cc with workshop tools, 0.14 f/cc for hand-tool gasket removal, and about 0.40 f/cc or less for packing work. For those tasks, 8-hour averages were 0.008 to 0.024 f/cc, and 0.085 f/cc for wet gasket removal. Band-sawing gasket sheet gave 2.2 to 4.9 f/cc. One study reported 3.7 f/cc for scraping and brushing small gaskets and 15.3 f/cc for large ones; the authors questioned its methods. The authors concluded that installing and removing these materials should not have posed a significant health hazard. They noted studies differed in methods and often lacked background measurements.

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 of published and selected unpublished air-sampling studies (simulation and work-site industrial hygiene studies)
• Who was studied: Seven simulation studies (or series of studies) and four work-site studies of industrial and maritime settings, involving more than 300 air samples
• Exposure: Airborne fibers from asbestos-containing gaskets and packing during removal and installation, flange cleaning and gasket formation
• Main results:
  • Bulk samples of gaskets and packing analyzed in the simulation studies contained chrysotile but not amphibole fibers
  • In all but one of the studies of gasket and packing replacement using hand-held tools, short-term average exposures were below the current 30-minute OSHA excursion limit of 1 f/cc
  • Gasket formation with workshop tools: average short-term concentration 0.44 f/cc and 8-hour TWA 0.008 f/cc
  • Gasket formation with hand-held manual tools: short-term concentrations near 0.1 f/cc; 8-hour TWA about 0.01 f/cc
  • Gasket removal and flange face cleaning with hand tools: 0.14 f/cc for peak concentrations and 0.024 f/cc over the 8-hour workday
  • Gasket installation (no removal or cleaning): about 0.15 f/cc short-term
  • Packing removal and installation: about 0.40 f/cc or less during peak exposures; about 0.01 f/cc over the 8-hour workday
  • Wet gasket removal (two work-site studies): average 0.085 f/cc for an 8-hour exposure
  • Band-sawing of compressed asbestos gasket material (Fowler study): four short-term breathing zone samples ranged from 2.2 to 4.9 f/cc, average 3.33 f/cc
  • One simulation study (Longo et al.) reported average breathing-zone concentrations by PCM of 3.7 f/cc (n=14) for scraping and brushing small gaskets and 15.3 f/cc (n=10) for large gaskets; the reviewing authors said its methods were inconsistent with other studies (overloaded filters, chamber not cleaned before power wire brushing)
  • The authors identified power wire brushing of residual gasket material as the only activity that in many cases may have produced breathing-zone concentrations near or above the 1 f/cc excursion limit
• The authors' conclusion: The authors concluded that the weight of evidence indicates installing and removing asbestos gaskets and packing should not have posed a significant health hazard
• Limitations the authors state:
  • Differences among the studies in sampling times, methods and activities made direct comparison difficult
  • Some studies did not measure background concentrations
  • Many studies did not report how long activities took or how often they were repeated, making 8-hour estimates difficult
  • The data relied on phase-contrast microscopy (PCM), which does not count all respirable asbestos fibers

Topics

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

Related studies

• An exposure study of bystanders and workers during the installation and removal of asbestos gaskets and packing — C. Mangold, K. Clark, 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)
• Airborne asbestos exposures associated with work on asbestos fire sleeve materials — C.L. Blake, S.C. Harbison, et al. (2011)
• Historical ambient airborne asbestos concentrations in the United States - an analysis of published and unpublished literature (1960s-2000s) — A. Abelmann, M.E. Glynn, et al. (2015)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)

Browse more research in Journal of Toxicology and Environmental Health. Part B, Critical Reviews, or return to medical research.