Simulation tests to assess occupational exposure to airborne asbestos from asphalt-based roofing products

Our plain-English summary of Simulation tests to assess occupational exposure to airborne asbestos from asphalt-based roofing products, by F. Mowat, R. Weidling, P. Sheehan (The Annals of Occupational Hygiene, 2007).

The study

• Authors: F. Mowat, R. Weidling, P. Sheehan
• Journal: The Annals of Occupational Hygiene
• Published: 2007;51(5):451-62
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study sought to evaluate exposure from specific products to evaluate potential risk from roof repair activities. Five asbestos-containing fibered roof coatings and plastic cements, representing a broad range of these types of products, were tested in exposure simulations. These products were applied to representative roof substrates. Release of asbestos fibers during application and sanding of the product shortly thereafter (wet sanding) were tested initially. Other roof substrates were cured to simulate a product that had been on a rooftop for several months and then were tested to evaluate release of fibers during hand sanding and hand scraping activities. Additional tests were also conducted to evaluate asbestos release during product removal from tools and clothing. Two personal (n = 84) and background/clearance (n = 49) samples were collected during each 30-min test and analyzed for total fiber concentration [phase-contrast microscopy (PCM)] and for asbestos fiber count [transmission electron microscopy (TEM)]. PCM concentrations ranged from <0.005 to 0.032 fibers per cubic centimeter (f cc(-1)). Chrysotile fibers were detected in 28 of 84 personal samples collected. TEM concentrations ranged from <0.0021 to 0.056 f cc(-1). Calculated 8-h time-weighted averages (TWAs) ranged from 0.0003 to 0.002 f cc(-1) and were comparable to the background TWA concentration of 0.0002 f cc(-1) measured in this study. Based on these results, it is unlikely that roofers were exposed to airborne asbestos concentrations above the current or historical occupational guidelines during scraping and sanding of these products during roof repair.

In plain English

This laboratory simulation tested five asphalt-based roofing products containing chrysotile asbestos. Three were fibered roof coatings (B-10, 201, D-21) and two were plastic roof cements (C-8, C-30). They had been sold in the 1950s to 1970s and were re-made in 2005. They were applied to non-asbestos roof panels, some oven-cured to represent several months on a roof. Workers hand sanded and scraped all five cured products. Application, wet sanding and removal from clothing and tools were tested only with B-10 and C-8. Breathing-zone air was sampled. Chrysotile was found in 28 of 84 personal samples. None was found during application, wet sanding or tool tests. Asbestos concentrations ranged from less than 0.0021 to 0.056 fibers per cubic centimeter. Estimated 8-hour averages assumed 30 minutes of the task, with the test-room background of 0.0002 fibers per cubic centimeter for the other 7.5 hours. These averages were 0.0003 to 0.002 fibers per cubic centimeter. The authors concluded asbestos had a low probability of becoming airborne from such products. They noted that long-term weathering, aggressive cutting or tear-out, and field removal were untested, and that high ventilation may have diluted concentrations.

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 exposure simulation study: asbestos-containing roofing products were applied to constructed roof panels and manipulated in test chambers. Personal breathing-zone air samples were collected and analyzed by PCM (total fibers) and TEM (asbestos fibers).
• Who was studied: No human population was studied. Five roofing products historically sold by Monsey Products Company and Henry Company were re-made in June 2005 and applied to non-asbestos roof panels. Removal tasks were performed by abatement technicians from MARCOR Environmental in test chambers at a facility in Hayward, CA. The study collected 84 personal samples and 49 background/clearance samples.
• Exposure: The products were three fibered roof coatings and two plastic roof cements containing chrysotile asbestos: B-10 (3.04%), 201 (4.9%), D-21 (4.24%), C-8 (15.5%) and C-30 (4.3%). Each test lasted 30 minutes. Hand scraping and hand sanding were done on all five cured products (oven-cured to represent several months on a roof). Application, wet sanding, and removal from laundered clothing and soiled tools were done only with C-8 and B-10.
• Main results:
  • Total fibers (asbestos and non-asbestos), measured by PCM, were detected in 38 of the 84 personal samples. Concentrations ranged from less than 0.005 to 0.032 fibers per cubic centimeter.
  • Asbestos fibers were detected by TEM in 28 of 84 personal samples, with 0 to 26 asbestos fibers per sample. All detected fibers were chrysotile. TEM asbestos concentrations ranged from less than 0.0021 to 0.056 fibers per cubic centimeter.
  • No asbestos fibers were identified in the application, wet sanding or tool tests, so 8-hour averages were not calculated for those tasks. The highest asbestos fiber counts came from hand sanding of cured product.
  • Estimated 8-hour time-weighted averages ranged from 0.0003 to 0.002 fibers per cubic centimeter. They assumed 30 minutes of the task, with the study's estimated background of 0.0002 fibers per cubic centimeter applied to the remaining 7.5 hours.
  • Of 42 background/clearance samples taken around the tests, two each contained a single asbestos fiber.
• The authors' conclusion: The authors concluded that the simulation indicated a low probability of asbestos becoming airborne during manipulation of coating- and cement-type roofing products such as those tested. They stated that the 8-hour averages were 100-fold below the current OSHA limit of 0.1 fibers per cubic centimeter.
• Limitations the authors state:
  • The study did not evaluate the effect of long-term weathering of the roofing products.
  • The relatively high air exchange rate in the test chambers may have diluted airborne asbestos concentrations.
  • More aggressive cutting, tear-out and sawing were not tested.
  • Exposure during removal in the field was not measured.
  • Low fiber counts meant wide variability in the acceptable range of fiber counts.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Transmission Electron Microscopy (TEM), Fibers per Cubic Centimeter (f/cc), Chrysotile, Personal Breathing Zone Sample, Time-Weighted Average (TWA).

Related studies

• Simulation tests to assess occupational exposure to airborne asbestos from artificially weathered asphalt-based roofing products — P. Sheehan, F. Mowat, et al. (2010)
• Occupational exposure to airborne asbestos from coatings, mastics, and adhesives — D.J. Paustenbach, A. Sage, et al. (2004)
• Exposure to airborne asbestos during abatement of ceiling material, window caulking, floor tile and roofing material — J.H. Lange, S.L. Sites, et al. (2008)
• Exposure to airborne asbestos during abatement of ceiling material, window caulking, floor tile, and roofing material — J.H. Lange, S.L. Sites, et al. (2006)
• The Production of Corporate Research to Manufacture Doubt About the Health Hazards of Products: An Overview of the Exponent Bakelite® Simulation Study — D. Egilman (2018)
• Occupational exposure to airborne asbestos from phenolic molding material (Bakelite) during sanding, drilling, and related activities — F. Mowat, M. Bono, et al. (2005)

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