Characterizing and Communicating Risk with Exposure Reconstruction and Bayesian Analysis: Historical Locomotive Maintenance/Repair Associated with Asbestos Woven Tape Pipe Lagging

Our plain-English summary of Characterizing and Communicating Risk with Exposure Reconstruction and Bayesian Analysis: Historical Locomotive Maintenance/Repair Associated with Asbestos Woven Tape Pipe Lagging, by F.W. Boelter, J.D. Persky, D.M. Podraza, et al (Risk Analysis, 2016).

The study

• Authors: F.W. Boelter, J.D. Persky, D.M. Podraza, W.H. Bullock
• Journal: Risk Analysis
• Published: 2016;36(2):228-43
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Our reconstructed historical work scenarios incorporating a vintage 1950s locomotive can assist in better understanding the historical asbestos exposures associated with past maintenance and repairs and fill a literature data gap. Air sampling data collected during the exposure scenarios and analyzed by NIOSH 7400 (PCM) and 7402 (PCME) methodologies show personal breathing zone asbestiform fiber exposures were below the current OSHA exposure limits for the eight-hour TWA permissible exposure limit (PEL) of 0.1 f/cc (range <0.007-0.064 PCME f/cc) and the 30-minute short-term excursion limit (EL) of 1.0 f/cc (range <0.045-0.32 PCME f/cc) and orders of magnitude below historic OSHA PEL and ACGIH TLVs. Bayesian decision analysis (BDA) results demonstrate that the 95th percentile point estimate falls into an AIHA exposure category 3 or 4 as compared to the current PEL and category 1 when compared to the historic PEL. BDA results demonstrate that bystander exposures would be classified as category 0. Our findings were also significantly below the published calcium magnesium insulations exposure range of 2.5 to 7.5 f/cc reported for historic work activities of pipefitters, mechanics, and boilermakers. Diesel-electric locomotive pipe systems were typically insulated with a woven tape lagging that may have been chrysotile asbestos and handled, removed, and reinstalled during repair and maintenance activities. We reconstructed historical work scenarios containing asbestos woven tape pipe lagging that have not been characterized in the published literature. The historical work scenarios were conducted by a retired railroad pipefitter with 37 years of experience working with materials and locomotives.

© 2015 The Authors. Risk Analysis published by Wiley Periodicals, Inc. on behalf of Society for Risk Analysis.

In plain English

In this exposure reconstruction study, the authors re-created past locomotive maintenance tasks involving asbestos woven tape pipe lagging. Over three days in a Baltimore museum repair shop, a retired pipefitter with 37 years of experience and a helper repaired simulated steam pipe leaks and handled air compressor pipes on a 1952 diesel-electric locomotive. Survey samples of the original lagging contained 40% to 80% chrysotile, and tape removed from one compressor pipe contained 90%. The steam pipe wrap's inner stuffing also contained amosite. Eight-hour personal asbestos fiber levels for the pipefitter and helper ranged from <0.007 to 0.064 PCME f/cc. Thirty-minute task levels ranged from <0.045 to 0.321 PCME f/cc, highest during dry-tape re-wrapping by the pipefitter. Bayesian analysis of total fiber data gave a 60% likelihood that the 95th percentile exposure equaled or exceeded the current OSHA limit of 0.1 f/cc. Against the 1976 limit of 2 f/cc, there was an 87% probability of category 1, a 95th percentile at or below one-tenth of the limit. The authors concluded that exposures were lower than historic and present OSHA limits. The air compressor itself was not removed.

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 reconstruction (simulation) study of historical work tasks, with personal and area air sampling analyzed by NIOSH 7400 (PCM) and 7402 (PCME), and Bayesian decision analysis
• Who was studied: One retired railroad pipefitter with 37 years' experience and a helper, who was a certified industrial hygienist. They worked over three days on a 1952 EMD F7A diesel-electric locomotive (former Western Maryland Railway No. 236) at the B&O Railroad Museum repair facility in Baltimore, MD.
• Exposure: Removal and re-wrapping of asbestos woven tape pipe lagging during two tasks: simulated steam pipe leak repair (chisel, hammer and oxy-fuel welding) and air compressor pipe maintenance. Survey samples of the original lagging (Table I) contained 40% to 80% chrysotile. Original tape removed from the compressor discharge pipe during the work (Table II) contained 90% chrysotile. The steam pipe inner stuffing contained 45% to 50% amosite plus 45% chrysotile. The Chinese-made replacement tape contained chrysotile. Two chrysotile-containing gaskets were also removed.
• Main results:
  • Original woven tape removed from the compressor-to-reservoir (discharge) pipe during the reconstruction contained 90% chrysotile.
  • Personal time-weighted average (TWA) asbestos fiber concentrations for the pipefitter and helper together ranged from <0.007 to 0.064 PCME f/cc.
  • Thirty-minute personal task (excursion) concentrations for the worker and helper ranged from <0.045 to 0.321 PCME f/cc.
  • Day 1 (pipe leak repair): the pipefitter's eight-hour TWA was 0.064 PCME f/cc and the helper's was 0.012 PCME f/cc.
  • Days 2 and 3 (equipment maintenance/repair): the pipefitter's eight-hour TWA ranged from 0.013 to 0.027 PCME f/cc, and the helper's ranged from <0.007 to 0.050 PCME f/cc.
  • The highest 30-minute task sample came when the pipefitter re-wrapped a pipe with dry woven tape: 0.368 f/cc total fibers (PCM) and 0.321 f/cc asbestos fibers (PCME).
  • Area sample TWA concentrations ranged from <0.006 to <0.007 PCME f/cc.
  • Visible dust was generated when the pipefitter chiseled off the old woven tape.
  • Bayesian analysis of total fiber (PCM) data for the pipefitter and helper was compared with the current OSHA limit of 0.1 f/cc. It gave a 60% likelihood that the 95th percentile exposure was equal to or greater than that limit (category 4). It gave a 40% likelihood that the 95th percentile was between 50% and 100% of the limit (category 3).
  • Bayesian analysis of asbestos fiber (PCME) data for the pipefitter and helper (Days 2 and 3, per the figure) gave an even split between category 3 and category 4 against the current OSHA limit.
  • Compared with the historical (1976) OSHA eight-hour limit of 2 f/cc, the total fiber (PCM) data gave an 87% decision probability of category 1, meaning a 95th percentile at or below 10% of the limit.
  • For potential bystanders, the 30-minute PCM data were compared with the current OSHA 30-minute limit of 1 f/cc. This gave a 65% likelihood of category 1 and a 35% likelihood of category 0.
  • The authors reported that, where similar tasks were done with both vacuumed (prepared) and dusty (unprepared) replacement tape, neither produced airborne concentrations exceeding the occupational exposure limit.
• The authors' conclusion: The authors concluded that exposures in their study were lower than the historic OSHA limits of 12 f/cc (1971 to 1976) and 2 f/cc (1976 to 1986). They also concluded that exposures were lower than the present OSHA limits of 0.1 f/cc (eight-hour TWA) and 1 f/cc (30-minute excursion limit).
• Limitations the authors state:
  • Because of its weight and time constraints, the air compressor unit itself was not physically removed during the maintenance scenario.
  • The steam generator and its piping had already been removed from the study locomotive, so the air compressor was used for the equipment scenario instead.
  • Unlike the vintage tape, the modern replacement tape was dusty. HEPA vacuuming did not remove all the dust, and both vacuumed and unvacuumed tape were used.
  • The Bayesian analysis assumed the exposure data follow a lognormal distribution.

Topics

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

Medical terms in this study, explained in our Lexicon: Exposure Reconstruction, Pipe Covering, Asbestos Exposure, Air Sampling, NIOSH Method 7400, Asbestiform, OSHA, Permissible Exposure Limit (PEL).

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