Airborne asbestos exposures associated with work on asbestos fire sleeve materials

Our plain-English summary of Airborne asbestos exposures associated with work on asbestos fire sleeve materials, by C.L. Blake, S.C. Harbison, G.T. Johnson, et al (Regulatory Toxicology and Pharmacology, 2011).

The study

• Authors: C.L. Blake, S.C. Harbison, G.T. Johnson, R.D. Harbison
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2011;61(2):236-42
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos-containing fire sleeves have been used as a fire protection measure for aircraft fluid hoses. This investigation was conducted to determine the level of airborne asbestos fiber exposure experienced by mechanics who work with fire sleeve protected hoses. Duplicate testing was performed inside a small, enclosed workroom during the fabrication of hose assemblies. Personal air samples taken during this work showed detectable, but low airborne asbestos fiber exposures. Analysis of personal samples (n=9) using phrase contract microscopy (PCM) indicated task duration airborne fiber concentrations ranging from 0.017 to 0.063 fibers per milliliter (f/ml) for sampling durations of 167-198 min, and 0.022-0.14 f/ml for 30 min samples. Airborne chrysotile fibers were detected for four of these nine personal samples, and the resulting asbestos adjusted airborne fiber concentrations ranged from 0.014 to 0.025 f/ml. These results indicate that work with asbestos fire sleeve and fire sleeve protected hose assemblies, does not produce regulatory noncompliant levels of asbestos exposure for persons who handle, cut and fit these asbestos-containing materials.

Copyright © 2011 Elsevier Inc. All rights reserved.

In plain English

In this controlled experiment, an FAA-licensed mechanic built aircraft hose assemblies with fire sleeves. The work was done in a small, closed, unventilated hangar room in Georgia in June 2008. The sleeves came from an aircraft whose original hose assemblies were tagged with 1970 assembly dates, and their braided fabric was 90% chrysotile. Sleeves were cut with a knife in one session and a hacksaw in another, and the debris was then swept up. Fibers were counted by phase contrast microscopy and checked for asbestos by electron microscopy. In the knife session, no asbestos was detected in either full-length personal sample. A 30-minute sample from that session had an asbestos-adjusted level of 0.0024 f/ml. In the hacksaw session, the full-length personal samples had asbestos-adjusted levels of 0.018 and 0.014 f/ml. In 30 minutes of sweeping, one of two personal samples showed 0.025 f/ml asbestos. No asbestos fibers were detected in outdoor samples. The authors reported that all levels were below current OSHA limits. They concluded that the results indicate an absence of substantive asbestos exposure risk for aircraft mechanics who handle or fabricate these assemblies.

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: Controlled exposure simulation: two hose-construction test sessions (about 3 hours each) and one 30-minute cleanup test, with personal and area air sampling
• Who was studied: One FAA-licensed airframe and engine mechanic working in a closed 3.05 by 4.01 m test room inside a hangar at Cartersville-Bartow County Airport, Georgia, USA, on June 17 and 18, 2008. There were nine personal air samples in total.
• Exposure: Stratoflex 2607 fire sleeves removed from an SA 226 Sweringen Merlin III turboprop aircraft. Tags on the original hose assemblies gave 3rd quarter 1970 assembly dates. The braided fabric was 90% chrysotile by polarized light microscopy. Tasks were cutting the sleeves (razor knife in session 1, hacksaw in session 2), dipping the ends, fitting the sleeves over hoses with compressed air, and sweeping up debris.
• Main results:
  • Session 1 (knife cutting): the two full-length personal samples measured 0.017 and 0.030 f/ml total fibers by phase contrast microscopy (mean 0.024 f/ml). Electron microscopy found no asbestos in either.
  • Session 1: the 30-minute personal sample taken during fire sleeve installation measured 0.022 f/ml total fibers. Electron microscopy showed 11% asbestos, giving an asbestos-adjusted level of 0.0024 f/ml.
  • Session 2 (hacksaw cutting): the full-length personal samples measured 0.036 and 0.063 f/ml total fibers (mean 0.050 f/ml). Asbestos-adjusted levels were 0.018 and 0.014 f/ml (mean 0.016 f/ml).
  • Session 2: the short-term personal samples taken during sleeve installation measured 0.23 f/ml (30 minutes) and 0.12 f/ml (15 minutes) total fibers. Electron microscopy detected no asbestos fibers in either.
  • Cleanup (30 minutes of sweeping): personal samples measured 0.14 and 0.076 f/ml total fibers. No asbestos was found in the first. The second was 33% asbestos, giving an asbestos-adjusted level of 0.025 f/ml.
  • Area samples in the test room: only one sample, from session 2, contained asbestos (16.7% of fibers), giving an asbestos-adjusted level of 0.003 f/ml over 167 minutes.
  • Outdoor samples measured 0.0011 to 0.0056 f/ml total fibers. Electron microscopy detected no asbestos fibers in them.
  • The authors reported that all measured concentrations were below the OSHA 8-hour and 30-minute excursion limits. The highest asbestos-adjusted task-duration concentration was less than 20% of the 0.1 f/cc limit.
• The authors' conclusion: The authors concluded that the results indicate an absence of substantive asbestos exposure risk to aircraft mechanics who handle or fabricate hose assemblies with asbestos-containing fire sleeves. They described their test conditions as worst case.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Personal Breathing Zone Sample, Chrysotile, Asbestos-Containing Material (ACM).

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