Airborne concentrations of asbestos onboard maritime shipping vessels (1978-1992)

Our plain-English summary of Airborne concentrations of asbestos onboard maritime shipping vessels (1978-1992), by D.M. Murbach, A.K. Madl, K.M. Unice, et al (The Annals of Occupational Hygiene, 2008).

The study

• Authors: D.M. Murbach, A.K. Madl, K.M. Unice, J.S. Knutsen, P.S. Chapman, J.L. Brown, D.J. Paustenbach
• Journal: The Annals of Occupational Hygiene
• Published: 2008;52(4):267-79
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The exposure of shipyard workers to asbestos has been frequently investigated during the installation, repair or removal of asbestos insulation. The same level of attention, however, has not been directed to asbestos exposure of maritime seamen or sailors. In this paper, we assemble and analyze historical industrial hygiene (IH) data quantifying airborne asbestos concentrations onboard maritime shipping vessels between 1978 and 1992. Air monitoring and bulk sampling data were compiled from 52 IH surveys conducted on 84 different vessels, including oil tankers and cargo vessels, that were docked and/or at sea, but these were not collected during times when there was interaction with asbestos-containing materials (ACMs). One thousand and eighteen area air samples, 20 personal air samples and 24 air samples of unknown origin were analyzed by phase contrast microscopy (PCM); 19 area samples and six samples of unknown origin were analyzed by transmission electron microscopy (TEM) and 13 area air samples were analyzed by scanning electron microscopy (SEM). In addition, 482 bulk samples were collected from suspected ACMs, including insulation, ceiling panels, floor tiles, valve packing and gaskets. Fifty-three percent of all PCM and 4% of all TEM samples were above their respective detection limits. The average airborne concentration for the PCM area samples (n = 1018) was 0.008 fibers per cubic centimeter (f cc(-1)) (95th percentile of 0.040 f cc(-1)). Air concentrations in the living and recreational areas of the vessels (e.g. crew quarters, common rooms) averaged 0.004 f cc(-1) (95th percentile of 0.014 f cc(-1)), while air concentrations in the engine rooms and machine shops averaged 0.010 f cc(-1) (95th percentile of 0.068 f cc(-1)). Airborne asbestos concentrations were also classified by vessel type (cargo, tanker or Great Lakes), transport status (docked or underway on active voyage) and confirmed presence of ACM. Approximately 1.3 and 0% of the 1018 area samples analyzed by PCM exceeded 0.1 and 1 f cc(-1), respectively. This data set indicates that historic airborne asbestos concentrations on these maritime shipping vessels, when insulation-handling activities were not actively being performed, were consistently below contemporaneous US occupational standards from 1978 until 1992, and nearly always below the current permissible exposure limit of 0.1 f cc(-1).

In plain English

The authors pooled industrial hygiene surveys from merchant ships, 1978 to 1992. The surveys came from consulting firms hired by ship owners and were supplied by shipping firms. These covered 1100 air and 482 bulk samples from 84 vessels. No air sampling was done during handling of asbestos materials. Asbestos-containing insulation was found on 28 of 42 ships with bulk samples. Bulk samples contained chrysotile and amosite; crocidolite appeared in three insulation samples and one ceiling panel. The 1018 area air samples averaged 0.008 fibers per cubic centimeter (f/cc). Crew areas averaged 0.004 and engine areas 0.010, a difference that was not statistically significant. About 1.3% exceeded 0.1 f/cc and none exceeded 1 f/cc. No samples exceeded the US occupational limits then in force. The 20 personal samples averaged 0.021 f/cc, significantly higher than area samples. The authors concluded that undisturbed asbestos insulation did not significantly increase seamen's exposure. They noted that most samples were counted by a method counting all fibers, not only asbestos, that methods changed over time, and that their data may be a subset of all measurements.

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: Retrospective analysis of pooled, previously unpublished historical industrial hygiene air and bulk sampling surveys (exposure assessment)
• Who was studied: Merchant shipping vessels (dry cargo, tankers, Great Lakes vessels and others): 1100 air samples and 482 bulk samples from 84 vessels, collected 1978 to 1992. The main data set was 1018 area air samples analyzed by phase contrast microscopy (PCM) from 74 vessels.
• Exposure: Background airborne fiber concentrations on ships, measured when no one was disturbing, repairing or handling asbestos-containing materials. Air samples were mostly analyzed by PCM, with a few by TEM and SEM. Bulk samples were taken from insulation, ceiling panels, floor tiles, gaskets and valve packing.
• Main results:
  • Ships with asbestos insulation: 28 of the 42 ships with bulk samples had asbestos-containing insulation.
  • Insulation samples: asbestos was detected in 232 of 392 bulk samples from pipe and equipment insulation.
  • Fiber types: of 287 quantitative bulk results, 153 contained one or more of amosite, chrysotile or crocidolite.
  • Chrysotile was detected in 140 quantitative bulk samples, from ceiling panels, floor tiles, gaskets, insulation, packing and samples of unknown origin.
  • Amosite was detected in 72 of the 245 quantitative bulk samples from insulation materials.
  • Crocidolite was found in four samples: three insulation samples and one ceiling panel.
  • All area air samples analyzed by PCM averaged 0.008 f/cc, with a 95th percentile of 0.040 f/cc.
  • By location: area samples averaged 0.004 f/cc in crew areas and 0.010 f/cc in engine compartments.
  • The crew-area mean was not significantly different from the engine-compartment mean.
  • Of the 1018 PCM area samples, approximately 1.3% exceeded 0.1 f/cc and 0% exceeded 1 f/cc.
  • The authors estimated with 95% confidence that only 2.1% of air concentrations may have exceeded 0.1 f/cc, and 0.7% may have exceeded 1 f/cc.
  • No air samples were above the OSHA permissible exposure limits in force at the time.
  • The 20 personal air samples averaged 0.021 f/cc, which was significantly higher than the average area concentration (P = 0.03).
  • Ships with confirmed asbestos insulation (28 ships) and ships not confirmed to have it (13 ships) both averaged 0.003 f/cc.
  • Samples taken while ships were docked averaged 0.010 f/cc and samples taken at sea averaged 0.005 f/cc; the difference was not statistically significant.
  • Only 1 of 25 TEM air samples was above its detection limit, at 0.124 f/cc.
• The authors' conclusion: The authors concluded that the mere presence of undisturbed asbestos-containing insulation on these ships did not significantly increase seamen's exposure to airborne asbestos. They also concluded that sailors on similar ships, docked and at sea, had minimal exposure to asbestos.
• Limitations the authors state:
  • Sampling and analysis were not consistent over time, and detection limits varied several-fold, because data were pooled from many firms and laboratories.
  • The higher values reported in earlier years may reflect differences in methods.
  • Area samples may not represent what workers actually breathed.
  • Most samples were analyzed by PCM, which counts all fibers rather than only asbestos fibers, so the authors considered the results an upper-bound estimate.
  • The data may be only a subset of all measurements, since they include only data the shipping firms provided to the authors.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Shipyards and maritime work.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Industrial Hygiene, Air Sampling, Bulk Sample Analysis, Asbestos-Containing Material (ACM), phase contrast microscopy (PCM), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM).

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