Chamber for testing asbestos-containing products: validation and testing of a re-created chrysotile-containing joint compound

Our plain-English summary of Chamber for testing asbestos-containing products: validation and testing of a re-created chrysotile-containing joint compound, by P.J. Sheehan, G.P. Brorby, D.W. Berman, et al (The Annals of Occupational Hygiene, 2011).

The study

• Authors: P.J. Sheehan, G.P. Brorby, D.W. Berman, K.T. Bogen, S.E. Holm
• Journal: The Annals of Occupational Hygiene
• Published: 2011;55(7):797-809
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Joint compound products containing chrysotile asbestos were commonly used for building construction from the late 1940s through the mid-1970s. Few relevant data exist to support reconstructing historical worker exposures to fibers generated by working with this material. Therefore, we re-created 1960s-era chrysotile-containing joint compound (JCC) and compared its characteristics to a current-day asbestos-free joint compound (JCN). Validation studies showed that a bench-scale chamber with controlled flow dynamics, designed to quantify particulate emissions from joint compound products, provided precise and reliable measurements of generated airborne dust mass, chrysotile fiber concentrations, and corresponding activity-specific emission rates. Subsequent chamber studies characterized fibers counted by phase contrast microscopy (PCM) per mass of respirable dusts and total suspended particulate dusts (total dusts), generated during JCC sanding or sweeping, as well as corresponding dust emission rates for JCC and JCN, and the ratio of total to respirable dust mass for JCN. From these data we estimated factors, F(CH-rd) and F(CH-td) (in units of f cm(-3) per mg m(-3)), by which respirable JCN dust mass concentrations collected during construction use can be converted to corresponding airborne PCM fiber concentrations generated by sanding or sweeping JCC. For sanding, median values (95% confidence limits) of F(CH-rd) and F(CH-td) were estimated to be 0.044 (0.039-0.050) and 0.212 (0.115-0.390) f cm(-3) per mg m(-3), respectively. The F(CH-td) to F(CH-rd) ratio indicates that approximately five times as many airborne PCM fibers are anticipated per unit air volume sampled when JCC dust is collected on cassettes (as done historically), than when respirable JCC dust is collected on cyclones. As the sizes of individual fibers collected appear to be primarily respirable, this difference may be a sampling artifact and suggests caution in interpreting historical fiber concentration measures made using cassettes during work with JCC-like materials. F(CH-rd) can be used with published and newly generated field measurements of respirable dust mass concentrations associated with the use of JCN or equivalent JCN materials to better characterize historical worker exposures to PCM fibers from use of JCC or equivalent JCCs. The experimental process described also can be used to develop conversion factors for other combinations of modern-day asbestos-free and historical chrysotile-containing products.

In plain English

In this laboratory study, the authors re-created a 1960s-era chrysotile-containing joint compound (JCC) and compared it with a current asbestos-free compound (JCN) by sanding and sweeping both in a bench-scale chamber. JCC gave off less respirable dust: the JCC-to-JCN emission rate ratio was 0.70 (95% confidence limits 0.63 to 0.79) for sanding and 0.53 (0.45 to 0.63) for sweeping. The authors calculated factors for converting respirable dust levels measured during JCN use into estimated airborne JCC fiber levels, counted by phase contrast microscopy. They said these estimates represent exposures from the tested JCC only to the extent that JCN dust measurements represent workers' exposures, under identical conditions. For sanding, the median factor was 0.044 (0.039 to 0.050) fibers per cubic centimeter per milligram of dust per cubic meter for respirable-dust (cyclone) samples. It was 0.211 (0.114 to 0.400) for total-dust (cassette) samples. For the same volume of air sampled, cassettes were expected to show about five times more fibers than cyclones. The authors suggested this may be a sampling artifact needing further study. They urged caution in interpreting historical cassette fiber measurements made during work with JCC-like materials.

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 bench-scale test chamber study comparing a re-created historical chrysotile-containing joint compound with a current asbestos-free joint compound
• Who was studied: Chamber test runs: for JCC, 10 sanding runs (four in Configuration 1, six in Configuration 2) and four sweeping runs; for JCN, 32 sanding runs and four sweeping runs. A total of 168 filters from the JCC runs were analyzed for asbestos fibers.
• Exposure: Dust and chrysotile fibers generated by sanding or sweeping a re-created 1960s-era chrysotile-containing calcium carbonate-based joint compound (JCC), compared with a current asbestos-free joint compound made by Georgia-Pacific (Toughrock All-Purpose Ready-Mix). Fibers were counted by phase contrast microscopy (PCM, NIOSH Method 7400 with 200 fields per filter). Respirable dust was collected on cyclones and total dust on open-face cassettes.
• Main results:
  • JCC fibers per microgram of dust, sanding: average 63 (95% confidence limits 57 to 69) in respirable dust and 26 (24 to 29) in total dust
  • JCC fibers per microgram of dust, sweeping: average 47 (42 to 52) in respirable dust and 19 (17 to 22) in total dust
  • Ratio of JCC to JCN respirable dust emission rates during sanding (cyclones and tubes combined): 0.70 (95% confidence interval 0.63 to 0.79), meaning JCC emitted less respirable dust
  • Ratio of JCC to JCN respirable dust emission rates during sweeping (sampling tubes only): 0.53 (0.45 to 0.63)
  • Ratio of JCC to JCN total dust (cassette) emission rates during sanding: 1.38 (95% confidence interval 1.03 to 1.85)
  • For sweeping, there was no evidence that the total dust emission rate ratio differed from 1 (P = 0.35)
  • Ratio of total to respirable JCN dust mass during sanding, predicted at the dust origin: 5.95 (95% confidence limits 4.16 to 8.51)
  • Median conversion factors for sanding JCC, in fibers per cubic centimeter per milligram of respirable dust per cubic meter: 0.044 (0.039 to 0.050) for cyclone (respirable) samples and 0.211 (0.114 to 0.400) for cassette (total dust) samples
  • Median conversion factors for sweeping JCC: 0.025 (0.022 to 0.029) for cyclone samples and 0.116 (0.079 to 0.169) for cassette samples
  • For the same volume of air sampled during JCC use, about five times more PCM fibers would be expected on cassette (total dust) samples than on cyclone (respirable dust) samples
• The authors' conclusion: The authors concluded that the chamber produced conversion factors for the materials tested. These factors can be combined with respirable dust measurements from JCN use to estimate historical PCM fiber exposures from JCC. They also concluded that the roughly five-fold cassette-to-cyclone difference may be a sampling artifact, which suggests caution in interpreting historical cassette-based fiber measurements during work with JCC-like materials.
• Limitations the authors state:
  • The authors' explanation for the cassette-to-cyclone difference (large, soft carbonate particles breaking up on cassette filters and releasing respirable fibers) is a working hypothesis. Further work is needed to see whether it fully explains the difference or applies only to carbonate-based joint compounds.
  • The estimated JCC fiber concentrations represent worker exposures only to the extent that respirable dust measurements from JCN use represent worker exposures, and only for use of the tested JCC under identical conditions.

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, Joint Compound, phase contrast microscopy (PCM).

Related studies

• Re-creation of historical chrysotile-containing joint compounds — G.P. Brorby, P.J. Sheehan, et al. (2008)
• More on the dynamics of dust generation: the effects of mixing and sanding chrysotile, calcium carbonate, and other components on the characteristics of joint-compound dusts — D.W. Berman, G.P. Brorby, et al. (2012)
• Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations — G.P. Brorby, P.J. Sheehan, et al. (2013)
• Potential artifacts associated with historical preparation of joint compound samples and reported airborne asbestos concentrations — G.P. Brorby, P.J. Sheehan, et al. (2011)
• Simulation tests to assess occupational exposure to airborne asbestos from artificially weathered asphalt-based roofing products — P. Sheehan, F. Mowat, et al. (2010)
• 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)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.