Asbestos exposure from the overhaul of a Pratt & Whitney R2800 engine

Our plain-English summary of Asbestos exposure from the overhaul of a Pratt & Whitney R2800 engine, by S.P. Mlynarek, D.R. Van Orden (Regulatory Toxicology and Pharmacology, 2012).

The study

• Authors: S.P. Mlynarek, D.R. Van Orden
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2012;64(2):189-94
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This study assessed the asbestos exposures of airplane piston engine mechanics while performing overhaul work on a Pratt & Whitney R2800 radial engine, with tools and practices in use since the time these engines were manufactured. Approximately 40% of the bulk samples collected during this test were found to contain chrysotile. Air samples were collected during the overhaul and were analyzed by phase contrast microscopy (PCM) and transmission electron microscopy (TEM). The average worker exposure during disassembly was 0.0272f/ml (PCM) and ranged from 0.0013 to 0.1240f/ml (PCM) during an average sample collection time of 188min. The average worker exposure during reassembly was 0.0198f/ml (PCM) and ranged from 0.0055 to 0.0913f/ml (PCM) during an average sample collection time of 222min. Only one worker sample (during reassembly) was found to contain asbestos at a concentration of 0.0012f/ml (PCME). Similar results should be found in other aircraft piston engines that use metal clad and non-friable asbestos gaskets, which are the current standard in aircraft piston engines.

Copyright © 2012 Elsevier Inc. All rights reserved.

In plain English

The authors measured airborne asbestos during a three-week overhaul of one Pratt & Whitney R2800-30W radial airplane piston engine at an FAA-certified repair facility in Idaho. Of 183 bulk samples of engine parts such as gaskets and seals, 73 (40%) contained asbestos, mostly chrysotile. One sealed metal o-ring held chrysotile and amosite. The authors said this material could only be reached by destroying the part, which a mechanic was unlikely to do. By phase contrast microscopy, which does not identify asbestos, mechanics averaged 0.0247 f/ml during disassembly and 0.0198 f/ml during reassembly, a difference that was not statistically significant. Electron microscopy found asbestos in 1 of 121 personal samples (a single chrysotile fiber, 0.0012 f/ml) and in 5 of 79 indoor area samples. The building's insulation coating and seam tape contained chrysotile. Task-based personal samples averaged below 0.05 f/ml, with no asbestos detected. The authors concluded the study reasonably suggests that, under customary conditions, mechanics' and bystanders' exposures are the same as or less than ambient background levels. They noted it was limited to one engine.

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 study: personal, bystander, indoor area and outdoor air sampling, plus bulk sampling of parts, during an overhaul and related service tasks performed on one engine
• Who was studied: Mechanics experienced in airplane piston engine work overhauling one Pratt & Whitney R2800-30W engine (accepted by the US Navy in 1948, stored from 1953). Cylinder changes and a clutch rebuild were done on parts from other R2800 engines. The work took place at Anderson Aeromotive, an FAA-certified repair station in Idaho. The article gives no date for the fieldwork.
• Exposure: Removal and installation of gaskets, o-rings, seals, clutch facings and similar parts, done by hand or with simple tools. Most asbestos-containing parts contained chrysotile; one contained chrysotile and amosite. The building also had chrysotile-containing insulation coating and tape.
• Main results:
  • Of 183 bulk samples from the overhaul and service work, 73 (40%) contained asbestos, with asbestos content from 20–30% to 60–70%.
  • All positive part samples contained chrysotile, except one cylinder sample: a sealed metal o-ring component whose inner material contained 25–35% chrysotile and 20–30% amosite.
  • The authors noted that the asbestos inside this sealed ring could only be reached by physically destroying the metal component, which they said a mechanic was not likely to do.
  • Mechanics' average fiber concentration by phase contrast microscopy (PCM), which does not identify which fibers are asbestos, was 0.0247 f/ml during disassembly (59 samples, average 188 min) and 0.0198 f/ml during reassembly (47 samples, average 222 min).
  • The difference in mechanics' PCM concentrations between disassembly and reassembly was not statistically significant (ANOVA p = 0.26; Mann–Whitney p = 0.49).
  • By transmission electron microscopy (TEM), 1 of 121 personal samples contained asbestos: one chrysotile fiber, collected on a mechanic on the last day of reassembly. The average for all worker samples was 0.000012 asbestos f/ml (PCME), and the maximum was 0.0012 asbestos f/ml.
  • By TEM, 5 of 79 indoor area samples contained asbestos, five chrysotile fibers in total. The average was 0.000028 asbestos f/ml (PCME) and the maximum 0.0011 asbestos f/ml. The authors said these samplers were not in the immediate vicinity of the work.
  • Indoor area PCM averages were 0.0056 f/ml during disassembly and 0.0046 f/ml during reassembly. This difference was not statistically significant (ANOVA p = 0.22; Mann–Whitney p = 0.41).
  • Task-based personal samples (clutch rebuild, cylinder change, ignition system, cut gasket) all averaged below 0.05 f/ml by PCM, and TEM detected no asbestos fibers in them.
  • The building's aluminized insulation coating contained chrysotile at 45–55% by weight, and the seam tape contained chrysotile at 20–30%. Areas of both were in poor condition.
• The authors' conclusion: The authors concluded that the study reasonably suggests that, during overhauls or service work on airplane piston engines under customary conditions, mechanics' and bystanders' asbestos exposures are the same as or less than ambient background levels, and several orders of magnitude below current and historic OSHA exposure regulations.
• Limitations the authors state:
  • The study was limited to one engine.
  • The engine was not returned to flight readiness, and some normal overhaul steps were skipped. The authors stated this had no effect on the asbestos exposure assessment.
  • No attempt was made to determine the air changes per hour in the building.
  • The task-based samples were limited in number.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Chrysotile, phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Friable, Gasket.

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