Occupational exposure to airborne asbestos from phenolic molding material (Bakelite) during sanding, drilling, and related activities

Our plain-English summary of Occupational exposure to airborne asbestos from phenolic molding material (Bakelite) during sanding, drilling, and related activities, by F. Mowat, M. Bono, R.J. Lee, et al (Journal of Occupational and Environmental Hygiene, 2005).

The study

• Authors: F. Mowat, M. Bono, R.J. Lee, S. Tamburello, D. Paustenbach
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2005;2(10):497-507
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

In this study, a historical phenolic (Bakelite) molding material, BMMA-5353, was tested to determine the airborne concentrations of asbestos fibers released during four different activities (sawing, sanding, drilling, and cleanup of dust generated from these activities). Each activity was performed for 30 min, often in triplicate. The primary objective for testing BMMA-5353 was to quantitatively determine the airborne concentration of asbestos fibers, if any, in the breathing zone of workers. Uses of this product typically did not include sawing or sanding, but it may have been drilled occasionally. For this reason, only small quantities were sawed, sanded, and drilled in this simulation study. Personal (n = 40), area (n = 80), and background/clearance (n = 88) air samples were collected during each activity and analyzed for total fiber concentrations using phase contrast microscopy (PCM) and, for asbestos fiber counts, transmission electron microscopy (TEM). The raw PCM-total fiber concentrations were adjusted based on TEM analyses that reported the fraction of asbestos fibers, to derive a PCM-asbestos concentration that would enable calculation of an 8-hour time-weighted average (TWA). The estimated 8-hour TWAs ranged from 0.006 to 0.08 fibers per cubic centimeter using a variety of worker exposure scenarios. Therefore, assuming an exposure scenario in which a worker uses power tools to cut and sand products molded from BMMA-5353 and similar products in the manner evaluated in this study, airborne asbestos concentrations should not exceed current or historical occupational exposure limits.

In plain English

This simulation study measured airborne asbestos released when a Bakelite-type phenolic molding material, BMMA-5353, was machined. For the test, the material was remade in a pilot plant in 2003 from historical formulation information. It contained 31% chrysotile asbestos by weight. In an indoor test chamber in Monroeville, Pennsylvania, a worker used power tools to band-saw, belt-sand and drill molded panels, and swept up the dust, in 30-minute tests. The authors described this as aggressive handling simulating a worst-case scenario. Air samples were analyzed by microscopy. Asbestos was detected in 25 of 40 personal (breathing-zone) samples. In personal samples, average asbestos concentrations were 0.11 fibers per cubic centimeter (f/cc) for sawing, 0.04 f/cc for sanding, below 0.01 f/cc for drilling and 0.02 f/cc for sweep cleanup. Using hypothetical workdays with 0.5 to 2 hours of these tasks, the authors estimated 8-hour average exposures of 0.006 to 0.08 f/cc. The authors concluded that these tasks would not, under any reasonably plausible scenario, be expected to produce asbestos levels above historical or current 8-hour occupational exposure 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: Exposure simulation study using material remade in 2003 to a historical formulation, with power-tool tasks intended to represent aggressive, worst-case handling
• Who was studied: Molded test panels of BMMA-5353, a phenolic molding compound originally made by Union Carbide from the late 1960s through 1974, worked by a single worker in a 58 cubic meter indoor test chamber in Monroeville, Pennsylvania. Samples taken: 40 personal, 80 area and 88 background/clearance air samples.
• Exposure: Airborne fibers from a Novolac phenolic resin containing 31% chrysotile asbestos (Jeffrey Mine 7RF-3) by weight. The fibers were released during band sawing, belt sanding, drill pressing and sweep cleanup, each test lasting 30 minutes.
• Main results:
  • Asbestos fibers were detected in 25 of the 40 personal samples, 52 of the 80 area samples, and 18 of the 88 background/clearance samples.
  • During sawing, asbestos was detected in all 6 personal and all 12 area samples. During drilling, it was measurable in only 1 of 8 personal and 2 of 16 area samples.
  • Personal (breathing-zone) samples gave average PCM-asbestos concentrations of 0.11 f/cc for sawing (range below 0.04 to 0.21), 0.04 f/cc for sanding (below 0.02 to 0.05), below 0.01 f/cc for drilling, and 0.02 f/cc for sweep cleanup (below 0.01 to 0.08).
  • Estimated 8-hour time-weighted averages for hypothetical worker scenarios (0.5 to 2 hours of tasks per day) ranged from 0.006 to 0.08 f/cc.
  • In the authors' worst-case scenario (2 hours each of sawing, sanding and drilling, plus 1.5 hours of sweeping), the estimated 8-hour average was no greater than 0.08 f/cc using maximum concentrations.
• The authors' conclusion: The authors concluded that sawing, sanding, drilling and dust cleanup of phenolic molding compounds, as done in this study, would not be expected under any reasonably plausible scenario to produce airborne asbestos above historical or current 8-hour occupational exposure limits.
• Limitations the authors state:
  • Not enough material was made to measure the remade product's impact, flexural or deflection strength against the ASTM specification.
  • Test duration was set by the limited quantity of remanufactured material available.
  • One of the four sawing replicates was aborted because the band saw failed, leaving three.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Jeffrey mine, Asbestos, Quebec

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Bakelite, Work Practice Simulation, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Time-Weighted Average (TWA), Fibers per Cubic Centimeter (f/cc).

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