Exposure data from multi-application, multi-industry maintenance of surfaces and joints sealed with asbestos-containing gaskets and packing

Our plain-English summary of Exposure data from multi-application, multi-industry maintenance of surfaces and joints sealed with asbestos-containing gaskets and packing, by F. Boelter, C. Simmons, P. Hewett (Journal of Occupational and Environmental Hygiene, 2011).

The study

• Authors: F. Boelter, C. Simmons, P. Hewett
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2011;8(4):194-209
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fluid sealing devices (gaskets and packing) containing asbestos are manufactured and blended with binders such that the asbestos fibers are locked in a matrix that limits the potential for fiber release. Occasionally, fluid sealing devices fail and need to be replaced or are removed during preventive maintenance activities. This is the first study known to pool over a decade's worth of exposure assessments involving fluid sealing devices used in a variety of applications. Twenty-one assessments of work activities and air monitoring were performed under conditions with no mechanical ventilation and work scenarios described as "worst-case" conditions. Frequently, the work was conducted using aggressive techniques, along with dry removal practices. Personal and area samples were collected and analyzed in accordance with the National Institute for Occupational Safety and Health Methods 7400 and 7402. A total of 782 samples were analyzed by phase contrast microscopy, and 499 samples were analyzed by transmission electron microscopy. The statistical data analysis focused on the overall data sets which were personal full-shift time-weighted average (TWA) exposures, personal 30-min exposures, and area full-shift TWA values. Each data set contains three estimates of exposure: (1) total fibers; (2) asbestos fibers only but substituting a value of 0.0035 f/cc for censored data; and (3) asbestos fibers only but substituting the limit of quantification value for censored data. Censored data in the various data sets ranged from 7% to just over 95%. Because all the data sets were censored, the geometric mean and geometric standard deviation were estimated using the maximum likelihood estimation method. Nonparametric, Kaplan-Meier, and lognormal statistics were applied and found to be consistent and reinforcing. All three sets of statistics suggest that the mean and median exposures were less than 25% of 0.1 f/cc 8-hr TWA sample or 1.0 f/cc 30-min samples, and that there is at least 95% confidence that the true 95th percentile exposures are less than 0.1 f/cc as an 8-hr TWA.

In plain English

This study pooled 21 asbestos exposure assessments the authors conducted from 1994 to February 2006. Experienced mechanics and tradesmen removed, made or replaced gaskets or packing (fluid sealing devices) on pumps, valves, faucets, car engines, farm tractors, heavy trucks and other equipment. Thirteen took place in an isolation test chamber, eight at field sites. None had mechanical ventilation; work was often dry and aggressive. Not all gaskets and packing contained asbestos; those that did mostly contained chrysotile, though one packing set contained crocidolite and one replacement gasket amosite. Only chrysotile was found in air samples analyzed by electron microscopy, and most of those analyses found no asbestos. Total fibers in 94 full-shift personal samples ranged from 0.0029 to 0.0848 fibers per cubic centimeter (f/cc). The authors reported that no measurement exceeded the 0.1 f/cc 8-hour or 1.0 f/cc 30-minute limits. One 30-minute sample exceeded half that limit; it was taken while grinding head gasket residue from a truck engine. The authors concluded that these devices have low fiber release potential. They noted that equipment could not be randomly selected.

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: Pooled analysis of 21 exposure assessments (simulated or field maintenance work with air monitoring) conducted by the authors; 13 in an isolation test chamber and 8 at field sites, all without mechanical ventilation
• Who was studied: Experienced mechanics and tradesmen working on equipment grouped into 10 categories: industrial/commercial pumps; pumps, fittings and check valves; industrial and maritime fittings; valve fittings; a commercial boiler; faucets; heavy machinery; automotive engines; farm equipment; and heavy trucks. Assessments were conducted from 1994 through February 2006. Samples: 782 analyzed by phase contrast microscopy (94 full-shift personal, 340 thirty-minute personal, 348 full-shift area) and 499 by transmission electron microscopy (70, 182 and 247 respectively).
• Exposure: Removal, making and/or replacement of gaskets and/or packing, often with dry and aggressive techniques (scraping, wire brushing, power grinding, compressed air). Not all gaskets and packing contained asbestos. Removed asbestos-containing materials contained up to 90% chrysotile, except one set of packing rings in assessment B containing 80% crocidolite. One replacement gasket in assessment Q contained 20% amosite.
• Main results:
  • Chrysotile was the only asbestos fiber type identified in air samples analyzed by transmission electron microscopy. No amphibole fibers were detected in any air sample.
  • No measurement exceeded the full-shift (0.1 f/cc 8-hr TWA) or 30-minute (1.0 f/cc) occupational exposure limits.
  • Personal full-shift TWA total fibers (94 samples, phase contrast microscopy): minimum 0.0029 f/cc, maximum 0.0848 f/cc, median 0.0244 f/cc, nonparametric 95th percentile 0.0569 f/cc (95% UCL 0.0828). Of these samples, 8.5% were censored.
  • Personal 30-minute total fibers (340 samples): minimum 0.0409 f/cc, maximum 0.9396 f/cc, nonparametric 95th percentile 0.2812 f/cc (95% UCL 0.3637). Of these samples, 51.5% were censored.
  • Most TEM analyses detected no asbestos fibers. In the asbestos-only data (Analysis 2), 77.1% of personal full-shift, 87.9% of area full-shift and 61% of personal 30-minute results were censored.
  • One 30-minute sample was over 50% of the 1 f/cc excursion limit. It came from heavy truck assessment T, during removal of head gasket residue with a power angle grinder fitted with an abrasive pad. The authors said it appeared to be an outlier.
  • The authors observed no consistent direct relationship between fiber release and more aggressive (higher-energy) removal. Aggressive activities produced the highest 30-minute result, but many aggressive activities also gave results below the limit of quantification.
• The authors' conclusion: The authors concluded that fluid sealing devices used across a wide variety of gasket and packing applications have low asbestos fiber release potential and result in low exposures. In their view, exposures above the occupational limits were unlikely regardless of how aggressive the work was.
• Limitations the authors state:
  • Equipment was chosen on availability, historical use knowledge and the expected presence of asbestos. Truly random selection of equipment was not possible.
  • Sample sizes within each assessment were relatively small, so only overall statistics for each data set were reported.
  • The asbestos-only data sets were severely censored (mostly non-detects), so the authors did not apply parametric (maximum likelihood) methods to them.

Topics

Medical terms in this study, explained in our Lexicon: Gasket, Fiber Release, Air Sampling, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Time-Weighted Average (TWA).

Related studies

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• Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — M.A. Atkinson, M. O'sullivan, et al. (2004)
• Re: Evaluation of the size and type of free particulates collected from unused asbestos-containing brake components as related to potential for respirability — D.J. Paustenbach, B.L. Finley, et al. (2006)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)
• Chamber for testing asbestos-containing products: validation and testing of a re-created chrysotile-containing joint compound — P.J. Sheehan, G.P. Brorby, et al. (2011)

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