A Bayesian Model and Stochastic Exposure (Dose) Estimation for Relative Exposure Risk Comparison Involving Asbestos-Containing Dropped Ceiling Panel Installation and Maintenance Tasks

Our plain-English summary of A Bayesian Model and Stochastic Exposure (Dose) Estimation for Relative Exposure Risk Comparison Involving Asbestos-Containing Dropped Ceiling Panel Installation and Maintenance Tasks, by F.W. Boelter, Y. Xia, J.D. Persky (Risk Analysis, 2017).

The study

• Authors: F.W. Boelter, Y. Xia, J.D. Persky
• Journal: Risk Analysis
• Published: 2017;37(9):1729-1741
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Assessing exposures to hazards in order to characterize risk is at the core of occupational hygiene. Our study examined dropped ceiling systems commonly used in schools and commercial buildings and lay-in ceiling panels that may have contained asbestos prior to the mid to late 1970s. However, most ceiling panels and tiles do not contain asbestos. Since asbestos risk relates to dose, we estimated the distribution of eight-hour TWA concentrations and one-year exposures (a one-year dose equivalent) to asbestos fibers (asbestos f/cc-years) for five groups of workers who may encounter dropped ceilings: specialists, generalists, maintenance workers, nonprofessional do-it-yourself (DIY) persons, and other tradespersons who are bystanders to ceiling work. Concentration data (asbestos f/cc) were obtained through two exposure assessment studies in the field and one chamber study. Bayesian and stochastic models were applied to estimate distributions of eight-hour TWAs and annual exposures (dose). The eight-hour TWAs for all work categories were below current and historic occupational exposure limits (OELs). Exposures to asbestos fibers from dropped ceiling work would be categorized as "highly controlled" for maintenance workers and "well controlled" for remaining work categories, according to the American Industrial Hygiene Association exposure control rating system. Annual exposures (dose) were found to be greatest for specialists, followed by maintenance workers, generalists, bystanders, and DIY. On a comparative basis, modeled dose and thus risk from dropped ceilings for all work categories were orders of magnitude lower than published exposures for other sources of banned friable asbestos-containing building material commonly encountered in construction trades.

© 2016 The Authors Risk Analysis published by Wiley Periodicals, Inc. on behalf of Society for Risk Analysis.

In plain English

This study measured airborne fibers while workers simulated tasks with asbestos-containing ceiling panels. The authors then used statistical models to estimate exposures for ceiling specialists, general tradesmen, maintenance workers, do-it-yourself persons such as homeowners, and bystanders. In two public schools in 2007, a worker repeatedly slid panels aside and replaced them. In an isolation chamber, a generalist cut and installed panels containing up to 4.5% amosite and up to 1.75% chrysotile. At the schools, long-term asbestos samples were below the limit of quantification (0.006 fibers/cc), and 30-minute asbestos samples were below a higher limit (0.045 fibers/cc). In the chamber, eight-hour average asbestos concentrations were 0.018 f/cc for the generalist and 0.019 f/cc for the bystander, and cutting produced higher levels than installing whole panels. Measured against the OSHA limit, the model rated maintenance workers' exposures "highly controlled" and the other groups' exposures "well controlled." Estimated one-year doses were highest for specialists. The authors noted that the data came from one manufacturer's panels and did not cover other asbestos sources. They concluded that the estimated doses were not in the range associated with elevated rates of lung cancer or mesothelioma.

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: Exposure assessment study: two field work simulations and one chamber work simulation, with air sampling, followed by Bayesian decision analysis and Monte Carlo modeling of eight-hour averages and one-year doses
• Who was studied: Simulated work in rooms with existing asbestos-containing dropped ceilings in two US public schools (Site A, a city school; Site B, a suburban school) in August 2007, plus an isolation chamber study. An experienced licensed asbestos abatement worker simulated a maintenance worker, and a generalist tradesman with over 30 years of experience did the chamber work. A certified industrial hygienist was monitored as a bystander. In total, 136 air samples were collected. Results were modeled for five groups: specialists, generalists, maintenance workers, do-it-yourself persons and bystanders.
• Exposure: Lay-in ceiling panels believed to have been manufactured by Conwed. At Site A, the panels contained 4.25% amosite, 3.25% amosite and 1.50% chrysotile. At Site B, one panel contained no asbestos, one contained 1.0% amosite, and one contained 1.25% amosite and 0.25% chrysotile. The chamber panels contained up to 4.5% amosite and up to 1.75% chrysotile. Tasks were sliding panels aside and replacing them (maintenance) and cutting and installing panels (generalist).
• Main results:
  • At both school sites, the long-term (full-shift personal and area) PCM-equivalent asbestos results were below the limit of quantification of 0.006 fibers/cc.
  • At both school sites, the 30-minute excursion asbestos results were reported as below a higher limit of quantification, 0.045 f/cc.
  • In the chamber study, the eight-hour average asbestos concentration (PCME) was 0.018 f/cc for the generalist and 0.019 f/cc for the bystander.
  • In the chamber, cutting produced higher concentrations than installing whole panels. For the generalist, asbestos concentrations were 0.011 f/cc while installing whole panels, 0.020 f/cc while cutting holes, and 0.022 f/cc while making 25 four-foot perimeter cuts.
  • Specialists, generalists and do-it-yourself persons (modeled as one exposure profile): the model gave a 95% probability that the 95th percentile of eight-hour exposure was less than 50% of the OSHA limit, a rating of "well controlled" (geometric mean 0.017 f/cc, GSD 1.68).
  • Maintenance workers: the model gave a 99% probability that the 95th percentile was less than 10% of the OSHA limit, a rating of "highly controlled" (geometric mean 0.006 f/cc, GSD 1.15).
  • Bystanders: the model gave a 97% probability that the 95th percentile was less than the OSHA limit and a 74% probability that it was less than 50% of the limit, a rating of "well controlled" (geometric mean 0.013 f/cc, GSD 2.34).
  • Estimated one-year doses were highest for specialists (mean 0.007 PCME f/cc-years; 5th to 95th percentile 0.005 to 0.010), followed by maintenance workers (mean 0.004; 0.002 to 0.005). Generalists, bystanders and do-it-yourself persons had means of 0.000, and do-it-yourself persons had the lowest doses.
• The authors' conclusion: The authors concluded that the predicted eight-hour average concentrations were not above current or historical occupational exposure limits. They also concluded that the estimated doses were not in the range associated with elevated rates of lung cancer or mesothelioma, and were orders of magnitude lower than published exposures for other friable asbestos-containing building materials.
• Limitations the authors state:
  • The data came from panels of one manufacturer (Conwed), with 1 to 5% amosite and less than 2% chrysotile. Generalizing the results should take panel composition and fiber type into account.
  • The dose estimates cover ceiling panel work only and do not include other likely asbestos sources in construction and maintenance trades.
  • Because there were no published historical data, the prior distributions in the Bayesian model were set by professional judgment.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Industrial Hygiene, Friable.

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