Airborne concentrations of chrysotile asbestos during operation of industrial crane controls and maintenance of associated arc chutes

Our plain-English summary of Airborne concentrations of chrysotile asbestos during operation of industrial crane controls and maintenance of associated arc chutes, by M.J. McCoy, R.C. Lewis, F.S. Mowat (Toxicology and Industrial Health, 2021).

The study

• Authors: M.J. McCoy, R.C. Lewis, F.S. Mowat
• Journal: Toxicology and Industrial Health
• Published: 2021;37(3):124-133
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Some industrial crane control panels were historically equipped with chrysotile-containing arc chutes. Because of the paucity of data regarding potential exposure from such equipment, we used a simulation approach to quantify the release of chrysotile from arc chutes in two functional 1970s-era industrial crane control panels during operation and maintenance. Two experienced operators separately simulated operation of crane controls under load; one of these operators then simulated two arc chute maintenance protocols: sanding (protocol 1) and scraping, sanding, and blowing (protocol 2). The original arc chutes contained approximately 36% chrysotile. Personal breathing zone (PBZ) (n = 8) and area samples (n = 8) were collected and analyzed using phase contrast microscopy (PCM) and transmission electron microscopy. PCM-equivalent (PCME) concentrations were derived, from which 8-h time-weighted averages (TWA) were calculated. During operation, chrysotile was identified in one of the four PBZ samples, equivalent to a PCME concentration of 0.012 f/cm3 (8-h TWA: 0.011 f/cm3). During protocols 1 and 2, chrysotile was identified in all PBZ samples (n = 4); PCME concentrations (and corresponding 8-h TWA) were <0.013 and 0.021 f/cm3 (0.001 and 0.004 f/cm3) and 0.013 and 0.017 f/cm3 (0.003 f/cm3), respectively. Many of the airborne chrysotile fibers had matrix attached, supporting the low exposure potential during this work. These data indicate very low, if any, exposures to chrysotile asbestos during the simulated scenarios. In addition, these data could assist with refining assumptions in exposure reconstruction and inform the state-of-the science on low-level chrysotile exposure.

In plain English

The authors simulated work with arc chutes in two 1970s-era industrial crane control panels. The arc chutes contained approximately 36% chrysotile asbestos by weight. Testing took place at an overhead crane training center in the Milwaukee, Wisconsin area in February 2018, with two experienced male volunteers. Both operated the crane controls under load for about 420 minutes with the panel doors open. One then sanded the arc chutes (protocol 1), and scraped, sanded and blew on them (protocol 2). During operation, chrysotile was found in one of four breathing-zone air samples, at 0.012 fibers per cubic centimeter (f/cm3), or 0.011 f/cm3 as an 8-hour average. During maintenance, chrysotile was found in all four breathing-zone samples. These measured less than 0.013 and 0.021 f/cm3 for sanding, and 0.013 and 0.017 f/cm3 for protocol 2. As 8-hour averages, which assumed no other asbestos exposure that day, they were 0.001 to 0.004 f/cm3. Many fibers had matrix material attached. The authors concluded exposures were very low, if any. They named the sample size and the range of products tested as limitations.

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: volunteers operated and then aggressively manipulated asbestos-containing arc chutes while personal and area air samples were collected and analyzed by phase contrast microscopy (PCM) and transmission electron microscopy (TEM)
• Who was studied: Two male volunteers experienced in operating and maintaining industrial crane controls: operator A, retired, over 25 years of experience; operator B, an overhead crane service engineer, over 20 years. They worked with two 1970s-era crane control panels made by P&H Crane Division, Harnischfeger Corporation, at an overhead crane training center in the Milwaukee, Wisconsin area in February 2018. In total, 16 air samples were collected: 8 personal breathing zone and 8 area.
• Exposure: Original cementitious mill-style arc chutes containing approximately 36% chrysotile asbestos by weight. Three activities were tested. (1) Operation of the crane controls under traverse and hoisting drive loads for about 420 minutes, with the panel doors open and operators about 4 feet away, a setup the authors designed to maximize exposure. (2) Protocol 1: sanding the arc chutes, about 65 minutes in total. (3) Protocol 2: scraping with a pocketknife, sanding and blowing on the arc chutes, about 70 minutes in total. Only operator A did the maintenance protocols.
• Main results:
  • No asbestos was identified in the three background area samples collected before the simulated activities.
  • During crane control operation, chrysotile was identified in one of the four personal breathing zone samples. That sample, from operator B's left lapel, had a PCM-equivalent concentration of 0.012 f/cm3, or 0.011 f/cm3 as an 8-hour time-weighted average. Chrysotile was also identified in the single area sample, at 0.006 f/cm3.
  • During both maintenance protocols, chrysotile was identified in all four personal breathing zone samples taken on operator A.
  • Personal breathing zone PCM-equivalent concentrations for operator A were less than 0.013 and 0.021 f/cm3 during protocol 1 (sanding), which is 0.001 and 0.004 f/cm3 as 8-hour time-weighted averages. During protocol 2 (scraping, sanding and blowing) they were 0.013 and 0.017 f/cm3, both 0.003 f/cm3 as 8-hour time-weighted averages.
  • Two area samples were taken at the interior face of the traverse crane control panel during protocol 2. They had PCM concentrations of 0.030 and 0.035 f/cm3, and chrysotile was identified in both.
  • Two area samples were collected about 4 feet from each control panel over the whole duration of both maintenance protocols. They had PCM concentrations of 0.013 and 0.014 f/cm3, and no chrysotile was identified in either.
  • Many of the chrysotile fibers seen by TEM had matrix material attached.
  • In personal breathing zone samples where asbestos was detected, calculated 8-hour time-weighted averages ranged from 0.001 to 0.011 f/cm3. The authors stated these were substantially lower than the current OSHA Permissible Exposure Limit of 0.1 f/cm3.
• The authors' conclusion: The authors concluded that the data indicate very low, if any, exposures to chrysotile asbestos during the simulated scenarios.
• Limitations the authors state:
  • The authors stated that the most obvious limitations were the sample size and the breadth of products tested.
  • No short-term samples were collected, so the results could not be compared directly with OSHA's 30-minute excursion limit of 1 f/cm3.
  • The count of 21 chrysotile fibers on one area sample at the panel face during protocol 2 may have been inflated, because fibrils within fiber bundles may have been counted as individual 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, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Time-Weighted Average (TWA), Personal Breathing Zone Sample, Exposure Reconstruction.

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