Airborne asbestos exposure during light aircraft brake replacement

Our plain-English summary of Airborne asbestos exposure during light aircraft brake replacement, by C.L. Blake, G.T. Johnson, R.D. Harbison (Regulatory Toxicology and Pharmacology, 2009).

The study

• Authors: C.L. Blake, G.T. Johnson, R.D. Harbison
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2009;54(3):242-6
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos containing materials are a component of many vehicle brake systems, including those found in some light aircraft. To characterize the asbestos exposure that results from the installation and maintenance of these components, an aircraft fitted with asbestos containing brake pads had brake changes performed while both area and personal air samples were taken. The brake changing process took place in a closed, unventilated aircraft hanger and all operations were performed according to the manufacturer's recommended procedure. Personal air samples did not detect any measurable amount of asbestos fibers during the brake changing or subsequent cleanup procedures. Analysis of personal samples (n=9) using phase contrast microscopy indicated airborne fiber concentrations at or below 0.003f/ml as 8-h time weighted averages (TWAs) and less than 0.069f/ml averaged over 28-30min sampling periods. Airborne chrysotile fibers were detected by two area air samples with fiber concentrations remaining at or below 0.0013f/ml over an 8-h TWA. These results indicate that normal brake changing work practices on aircraft with asbestos containing brake pads does not produce a harmful level of asbestos exposure for aircraft mechanics.

In plain English

One licensed mechanic replaced asbestos-containing brake pads on a 1961 Cessna 172 B in a closed, unventilated Georgia hangar while airborne fibers were measured. The pads had been worn down over 3 months of flying. Tests of two removed pads found 10% (by area) chrysotile asbestos. The mechanic did two brake changes, the second including compressed air blowout cleaning, followed by shop cleanup. Air was sampled at the mechanic's shoulders and at fixed spots in the hangar. Light microscopy found fibers in three of six personal samples taken during brake changing, but electron microscopy found no asbestos in them, only metal, organic and cellulose fibers. Chrysotile was found in two area samples, both taken during the brake change with compressed air blowout. Their levels were 0.0004 and 0.0013 fibers per milliliter (f/ml) as 8-hour time-weighted averages, calculated by assuming zero concentration outside the test, not measured across a full shift. Outdoor samples contained fibers but no asbestos. The authors concluded that light aircraft mechanics are not at risk from asbestos exposure during routine brake servicing and replacement.

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 (simulation of brake maintenance): two brake changes and a cleanup on one aircraft, with personal and area air sampling analyzed by phase contrast microscopy (PCM) and transmission electron microscopy (TEM)
• Who was studied: One licensed aircraft mechanic working on one 1961 Cessna Model 172 B aircraft, in an aircraft hangar at the Cartersville – Bartow County Airport, Georgia, USA; date of testing not stated
• Exposure: Changing worn Cleveland disc brake pads containing chrysotile asbestos (10% by area in each of the 2 pads analyzed), with the hangar closed and heating, ventilating and air conditioning shut down; the second change included compressed air blowout cleaning
• Main results:
  • Personal samples on the mechanic: fibers were found by PCM in three of the six samples taken during brake changing and in none of the samples taken during cleanup
  • TEM analysis of the fiber-positive personal samples found no asbestos fibers, only metal, organic and cellulose fibers
  • Highest personal PCM result as an 8-hour time-weighted average was 0.003 f/ml (left shoulder, left-wheel brake change); TEM fiber ratio for this sample was 0
  • The personal 8-hour time-weighted averages were calculated assuming no exposure other than the test
  • Area samples taken near the aircraft ranged from less than 0.00044 to 0.0016 f/ml as 8-hour time-weighted averages by PCM
  • Chrysotile was found in two area samples, both taken during the right-wheel brake change with compressed air blowout cleaning
  • The two chrysotile-positive area samples measured 0.0004 f/ml and 0.0013 f/ml PCM-equivalent concentrations as 8-hour time-weighted averages
  • The area 8-hour time-weighted averages were calculated assuming zero concentration outside the test period
  • Outdoor area samples showed fibers at 0.0014 to 0.0023 f/ml by PCM, but TEM found no asbestos, only organic, cellulose and gypsum fibers
• The authors' conclusion: The authors concluded that light aircraft mechanics are not at risk from asbestos exposure during routine servicing and replacement of asbestos-containing brake systems

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Brake Lining, Personal Breathing Zone Sample, phase contrast microscopy (PCM), Chrysotile.

Related studies

• Airborne asbestos concentration from brake changing does not exceed permissible exposure limit — C.L. Blake, D.R. Van Orden, et al. (2003)
• Airborne asbestos exposures associated with gasket and packing replacement: a simulation study of flange and valve repair work and an assessment of exposure variables — A.K. Madl, K.D. Devlin, et al. (2015)
• Airborne asbestos exposures associated with work on asbestos fire sleeve materials — C.L. Blake, S.C. Harbison, et al. (2011)
• Assessment of potential asbestos exposures from jet engine overhaul work — S.P. Mlynarek, D.R. Van Orden (2012)
• Asbestos exposure from the overhaul of a Pratt & Whitney R2800 engine — S.P. Mlynarek, D.R. Van Orden (2012)
• Evaluation of Airborne Asbestos Concentrations Associated with the Operation and Maintenance of Brakes and Clutches on Nonautomated Heavy Equipment — J. Sahmel, H. Avens, et al. (2022)

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