Airborne asbestos exposures associated with gasket and packing replacement: a simulation study of flange and valve repair work and an assessment of exposure variables

Our plain-English summary of Airborne asbestos exposures associated with gasket and packing replacement: a simulation study of flange and valve repair work and an assessment of exposure variables, by A.K. Madl, K.D. Devlin, A.L. Perez, et al (Regulatory Toxicology and Pharmacology, 2015).

The study

• Authors: A.K. Madl, K.D. Devlin, A.L. Perez, D.M. Hollins, D.M. Cowan, P.K. Scott, K. White, T.J. Cheng, J.L. Henshaw
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2015;71(1):35-51
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A simulation study was conducted to evaluate worker and area exposure to airborne asbestos associated with the replacement of asbestos-containing gaskets and packing materials from flanges and valves and assess the influence of several variables previously not investigated. Additionally, potential of take home exposures from clothing worn during the study was characterized. Our data showed that product type, ventilation type, gasket location, flange or bonnet size, number of flanges involved, surface characteristics, gasket surface adherence, and even activity type did not have a significant effect on worker exposures. Average worker asbestos exposures during flange gasket work (PCME=0.166 f/cc, 12-59 min) were similar to average worker asbestos exposures during valve overhaul work (PCME=0.165 f/cc, 7-76 min). Average 8-h TWA asbestos exposures were estimated to range from 0.010 to 0.062 f/cc. Handling clothes worn during gasket and packing replacement activities demonstrated exposures that were 0.71% (0.0009 f/cc 40-h TWA) of the airborne asbestos concentration experienced during the 5 days of the study. Despite the many variables considered in this study, exposures during gasket and packing replacement occur within a relatively narrow range, are below current and historical occupational exposure limits for asbestos, and are consistent with previously published data.

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In plain English

In this simulation study, a retired U.S. Navy mechanic replaced chrysotile-containing gaskets and valve packing on salvaged ship flanges and valves. The work took 5 days in 2011 in an enclosed chamber in Windsor, California. Removed gaskets were 45% to 95% chrysotile; no amphibole fibers were detected. Average worker exposure (PCME) was 0.166 fibers per cubic centimeter (f/cc) during flange gasket work and 0.165 f/cc during valve overhaul work. Ventilation, task, surface type, flange size and gasket adherence did not significantly affect worker exposure, though highly adhered gaskets took longer to remove. Area concentrations fell with distance by two of three counting methods. The authors assumed one to three 30 to 60 minute tasks daily, based on lawsuit testimony. On that basis they estimated 8-hour average worker exposures of 0.010 to 0.062 f/cc. A volunteer handling the coveralls for 15 minutes was exposed to an average of 0.143 f/cc. Spread over a 40-hour week assuming once-weekly handling, this equaled 0.0009 f/cc, 0.71% of the 40-hour average from the gasket and packing work. The authors concluded exposures were generally below current and historical occupational 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: Simulation study of flange gasket replacement and valve overhaul work in an enclosed test chamber, with personal and area air sampling and a simulated clothes-handling test
• Who was studied: One retired U.S. Navy mechanic did all the work. He worked on 28 equipment surfaces (19 pipe flanges, 3 valve bonnets, 6 valve flanges) salvaged from ship-breaking facilities in Canada and India, including the HMCS Fraser. There were 23 events over 5 days (March 1 and November 9 to 12, 2011) in Windsor, California, and 475 air samples were collected.
• Exposure: Chrysotile in gaskets and packing. Removed gaskets were 45% to 95% chrysotile and installed gasket material was 50% to 80% chrysotile. Removed packing was 80% to 90% chrysotile and installed packing was 40% to 85% chrysotile. No amphibole fibers were detected in these materials. Tasks were done with hand tools such as chisels, scrapers and hand wire brushes.
• Main results:
  • Average worker chrysotile concentrations (PCME) during flange gasket tasks were 0.194 f/cc for removal on a single flange, 0.136 f/cc for installation on a single flange, 0.139 f/cc for replacement on a single flange, and 0.091 f/cc for replacement on multiple flanges. The overall flange gasket average was 0.166 f/cc (54 samples, 12 to 59 min).
  • Average worker chrysotile concentration (PCME) for all tasks of a complete valve overhaul was 0.165 f/cc (28 samples, 7 to 76 min).
  • For the worker, there was no statistically significant difference in average chrysotile concentrations between tasks (p = 0.18, PCME).
  • For the worker, smooth versus phonographic flange surfaces showed no statistically significant difference in average chrysotile concentrations (p = 0.24, PCME).
  • For the worker, low versus high gasket surface adherence showed no statistically significant difference in fiber concentration.
  • Sample duration was significantly longer for gasket removals with high surface adherence than with low adherence (p = 0.0061).
  • Area (bystander) concentrations decreased significantly with distance from the work as measured by PCM and PCME, but not by TEM.
  • The authors' 8-hour work scenario drew on a qualitative review of testimony from over 60 workers who had filed lawsuits against gasket and packing manufacturers.
  • Assuming 1 to 3 gasket or packing tasks per day of 30 to 60 min each, estimated worker 8-hour TWA exposures ranged from 0.010 to 0.062 f/cc. The authors noted this was below the current Permissible Exposure Limit of 0.1 f/cc.
  • The volunteer handling the worn coveralls was exposed to an average of 0.143 f/cc during the 15-minute handling (PCME).
  • The authors assumed clothes handling happened once a week and spread the 15-minute exposure over a 40-hour week. The resulting 40-hour TWA was 0.0009 f/cc. This was 0.71% of the 0.127 f/cc 40-hour TWA for all gasket and packing work, including Events 4 and 14.
  • Two events on rusted, damaged flanges (Events 4 and 14) were judged unrealistic and excluded from the main analysis. In Event 4, worker samples during gasket removal averaged 0.695 f/cc (PCME; 6 samples, 24 to 68 min).
  • In size analysis of fibers on the worker's lapel, about 36 to 62% of fibers counted were outside the respirable size range, under the authors' definitions of a respirable fiber (diameter less than 0.7 or less than 3 micrometers).
• The authors' conclusion: The authors concluded that exposures during flange gasket replacement and complete valve overhaul were generally below current limits (0.1 f/cc 8-hour TWA; 1 f/cc 30-minute Excursion Limit) and historical occupational exposure limits. They also concluded the exposures were consistent with previously published data.
• Limitations the authors state:
  • The authors cautioned that because the variables tested did not significantly affect worker exposures, the data should not be scaled or extrapolated to other scenarios.
  • Installation samples taken as part of a full replacement may have been influenced by the preceding removal task.
  • Some worker samples could not be read: eight were overloaded with iron dust, and seven others were voided due to collection disturbances.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Gasket, Work Practice Simulation, Occupational Exposure.

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)
• 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)
• A meta-analysis of airborne asbestos fiber concentrations from work with or around asbestos-containing floor tile — A.L. Perez, M.L. Nelson, et al. (2018)
• Assessment of potential asbestos exposures from jet engine overhaul work — S.P. Mlynarek, D.R. Van Orden (2012)
• Airborne asbestos exposures associated with work on asbestos fire sleeve materials — C.L. Blake, S.C. Harbison, et al. (2011)
• Assessment of airborne asbestos exposure during the servicing and handling of automobile asbestos-containing gaskets — C.L. Blake, G.S. Dotson, et al. (2006)

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