Fiber release during the removal of asbestos-containing gaskets: a work practice simulation

Our plain-English summary of Fiber release during the removal of asbestos-containing gaskets: a work practice simulation, by W.E. Longo, W.B. Egeland, R.L. Hatfield, et al (Applied Occupational and Environmental Hygiene, 2002).

The study

• Authors: W.E. Longo, W.B. Egeland, R.L. Hatfield, L.R. Newton
• Journal: Applied Occupational and Environmental Hygiene
• Published: 2002;17(1):55-62
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Work practice studies were conducted involving the removal of asbestos-containing sheet gaskets from steam flanges. These studies were performed to determine potential exposure levels to individuals who have worked with these types of materials in the past and may still work with these products today. The work practices were conducted inside an exposure characterization laboratory (ECL) and were performed by scraping and wire brushing, chrysotile-containing (65% to 85%) sheet gaskets from a number of used steam flanges. Airborne asbestos levels were measured by phase contrast microscopy (PCM) and transmission electron microscopy (TEM) for the personnel and area air samples collected during the study. These workplace simulations showed substantial asbestos fiber release using scraping, hand wire brushing, and power wire brushing techniques during the gasket removal process. The range of concentration was 2.1 to 31.0 fibers/cc greater than 5 micrometers when measured by PCM. These results contrasted with the few reported results in the published literature where lower airborne asbestos levels were reported. In these studies the airborne asbestos fiber levels measured in many of the samples exceeded all current and historical Occupational Safety and Health Administration (OSHA) excursion limits (15-30 minutes) and some previous permissible exposure limits (PEL) based on eight-hour time-weighted average (TWA) standards. Also, individuals who performed this type of work in the past may have had exposures higher than previously suspected. The results demonstrated that employees who remove dry asbestos-containing gaskets with no localized ventilation should wear a full face supplied air respirator with a HEPA escape canister and the work area should be designated a regulated area.

In plain English

In this laboratory simulation, one of the authors removed used asbestos sheet gaskets from steam flanges inside a ventilated containment room while a second author acted as a helper. The flanges had been collected in 1994 from an Oregon paper mill powerhouse. The gaskets contained 65 percent to 85 percent chrysotile asbestos. Gaskets were scraped and hand wire brushed from small flanges (Study 1) and large flanges (Study 2), and leftover residue was removed with an electric wire brush (Study 3). Measured by phase contrast microscopy (PCM), the worker's peak levels were 10.1, 24.0 and 31.0 fibers per cubic centimeter (f/cc) in Studies 1, 2 and 3. The worker's 8-hour time-weighted averages were 1.5, 3.6 and 2.3 f/cc. Electron microscopy counts were about 30 times higher than PCM counts. Work surfaces and clothing were described as highly contaminated. The authors noted that gaskets that could be easily removed would not be expected to give comparable levels. They concluded that dry removal methods result in significant airborne exposures, with PCM levels exceeding all historical OSHA excursion limits.

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: Laboratory work practice simulation (exposure study), not a study of disease in people
• Who was studied: Used valve and steam flange assemblies collected in 1994 from a paper mill powerhouse in Oregon. Study 1 used seven small flange assemblies (ten gaskets), Study 2 used four large flange assemblies, and Study 3 used one large flange assembly. Two of the investigators were in the laboratory: one did all of the gasket removal and the other acted as a helper.
• Exposure: Sheet gaskets containing 65 percent to 85 percent chrysotile asbestos, removed dry by scraping with a putty knife, by hand wire brushing, and by power wire brushing with an electric drill and wire wheel
• Main results:
  • Study 1 (scraping and hand wire brushing, small flanges): the worker had a PCM peak of 10.1 f/cc and an 8-hour TWA of 1.5 f/cc
  • Study 2 (scraping and hand wire brushing, large flanges): the worker had a PCM peak of 24.0 f/cc and an 8-hour TWA of 3.6 f/cc
  • Study 3 (power wire brushing): the PCM peak was 31.0 f/cc and the calculated 8-hour TWA was 2.3 f/cc
  • Across the studies, PCM concentrations ranged from 2.1 to 31.0 fibers/cc longer than 5 micrometers
  • TEM analysis showed fiber concentrations about 30 times greater than PCM analysis
  • Surface dust on the work table and fabric from the investigators' work clothing were classified as highly contaminated
• The authors' conclusion: The authors concluded that dry removal methods typically used by machinists and pipefitters, past and present, result in significant airborne asbestos fiber exposures. They stated that the PCM-measured exposures in all three studies exceeded all historical OSHA excursion limits and some previous 8-hour permissible exposure limits.
• Limitations the authors state:
  • The area air samples in Study 1 were voided because the air-sampling lines into the laboratory were obstructed
  • The PCM concentrations in Study 1 decreased as the study progressed, which the authors attributed to particulate overloading on the filters
  • The authors stated that gaskets that could be easily removed would not be expected to produce airborne levels comparable to those found in these studies

Topics

Medical terms in this study, explained in our Lexicon: Fiber Release, Gasket, Work Practice Simulation, Chrysotile, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), OSHA, Excursion Limit.

Related studies

• 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)
• An exposure study of bystanders and workers during the installation and removal of asbestos gaskets and packing — C. Mangold, K. Clark, et al. (2006)
• Personal exposure during abatement of various asbestos-containing materials in the same work area — J.H. Lange, K.W. Thomulka, et al. (2005)
• Evaluation of asbestos-containing products and released fibers in home appliances — S.H. Hwang, W.M. Park (2016)
• Release of asbestos fibers during casting ring liner manipulation — D.R. Davis (1995)
• 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)

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