Releasability of asbestos fibers from weathered roof cement

Our plain-English summary of Releasability of asbestos fibers from weathered roof cement, by A.F. Oberta, L. Poye, S.P. Compton (Journal of Occupational and Environmental Hygiene, 2018).

The study

• Authors: A.F. Oberta, L. Poye, S.P. Compton
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2018;15(6):466-473
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile asbestos fibers were added to roofing products, including roof cement, for several decades. The fibers were described as "encapsulated" and therefore incapable of being released, an assertion that is disproved by the study reported herein. Three test panels of roof cement from the original container were exposed to ambient weathering in 2015 and 2016. Two panels were then sampled using the ASTM D5755 microvacuum method. Sampling revealed a light brown sub-layer under the dark brown surface layer, both of which crumbled and became friable during sampling. Analysis of the microvacuum samples with transmission electron microscopy showed that the material on the 2 panels contained 4,432,000 and 3,320,000 asbestos structures per cm² with nearly all of the structures consisting of fibers less than 5 µm long. Energy dispersive spectrometry determined that none of the fibers reported were coated with asphalt. The presence of free fibers was confirmed by direct examination of the surfaces of the panels and of dust released from handling the panels via scanning electron microscopy. This study confirmed the releasability of uncoated asbestos fibers from dried roof cement that was indicated in 2 previous studies published in 2007 and 2010. These results suggest that the finding of the Fifth Circuit Court in 1997 that uncoated airborne asbestos fibers cannot be released from roof cement, and therefore do not present a potential exposure by inhalation, was erroneous in retrospect. The exemption of roof cement from regulation under the Occupational Safety and Health Administration Construction Industry Standard for asbestos by the Court should not be relied on by employers of workers who remove weathered asbestos-containing roof cement, and precautions should be taken against exposure to airborne asbestos fibers during this work.

In plain English

In this weathering experiment, the authors spread Monsey Plastic Roof Cement, from a can bought in 1998, on three tile panels and hung them outdoors west of Austin, Texas, for nine months in 2015 and 2016. The cement contained 6.17% to 6.73% chrysotile asbestos by weight. When two panels were vacuum-sampled, the weathered surface crumbled. Electron microscopy found 4,432,000 asbestos fibers per square centimeter on the left panel and 3,320,000 on the center panel. All counted fibers were uncoated by asphalt, and 96.6% were no longer than 5 micrometers. Chrysotile fibers free of the binder were seen on panel surfaces, and fingertip-touch samples suggested such fibers could be transferred by contact. The authors concluded that removing dried roof cement can release asbestos fibers and create an inhalation hazard to workers. They noted that no unweathered control panels were made, the panels weathered for only nine months, and the article did not address airborne fiber levels or health effects.

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: Experimental weathering test of roof cement panels, followed by surface microvacuum sampling and electron microscopy (TEM and SEM)
• Who was studied: Three test panels: non-asbestos floor tile coated with a 1/8-inch layer of Monsey Plastic Roof Cement taken from a quart container bought in 1998. The panels were exposed outdoors west of Austin, Texas, from July to October 2015 and from April to October 2016.
• Exposure: Chrysotile asbestos in roof cement, measured in three sub-samples at 6.73%, 6.62% and 6.17% of original weight. The cement was weathered outdoors for a total of nine months during peak seasonal temperatures.
• Main results:
  • During microvacuum sampling, the weathered surface layer (which had changed from black to dark brown) crumbled and exposed a light brown sub-layer.
  • Asbestos loading was 4,432,000 fibers/cm² on the left panel (two samples combined, 195 structures counted) and 3,320,000 fibers/cm² on the center panel (100 structures counted).
  • 3.1% of fibers collected from the left panel were longer than 5 µm.
  • 4.0% of fibers collected from the center panel were longer than 5 µm. Overall, 96.6% of fibers meeting the counting criteria were not greater than 5 µm long.
  • All fibers reported in the microvacuum results and used to calculate loading were uncoated. Energy dispersive spectroscopy identified 295 fibers as chrysotile asbestos.
  • Direct examination of small cut sections of the weathered cement showed encapsulated, partially encapsulated and unencapsulated asbestos fiber bundles on the surfaces of the left and right panels.
  • Fingertip (dermal) transfer samples suggested that unencapsulated asbestos fibers were present on the surfaces of the left and right panels.
• The authors' conclusion: The authors concluded that removing dried roof cement as a friable material can release asbestos fibers and create an inhalation hazard to workers. They also stated that the 1997 court assertion that fibers in roof cement are encapsulated and cannot be released was erroneous in retrospect.
• Limitations the authors state:
  • No control panels unaffected by weathering were prepared.
  • The sampling was less aggressive than removal by workers with tools.
  • The panels were exposed for nine months, much shorter than the life of real roofs.
  • The dermal contact test does not measure how much fiber is released.
  • The study did not measure airborne fiber concentrations or address the health effects of inhaling the fibers.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, ASTM D5755, Friable, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM).

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)
• Mobilization of asbestos fibers by weathering of a corrugated asbestos cement roof — T. Ervik, S. Eriksen Hammer, et al. (2021)
• Risk assessment of the decay of asbestos cement roofs — A. Campopiano, D. Ramires, et al. (2009)
• Lichens on asbestos-cement roofs: bioweathering and biocovering effects — S.E. Favero-Longo, D. Castelli, et al. (2009)
• Mortality and cancer incidence among Lithuanian cement producing workers — G. Smailyte, J. Kurtinaitis, et al. (2004)
• Colorectal cancer in asbestos cement workers in Denmark — E. Raffn, E. Villadsen, et al. (1996)

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