A pilot study: fibre diameters of airborne asbestos dust (final report to the Institute of Occupational and Environmental Health)

Our plain-English summary of A pilot study: fibre diameters of airborne asbestos dust (final report to the Institute of Occupational and Environmental Health) (1972).

The study

• Published: Final report to the Institute of Occupational and Environmental Health (1972)
• Type of article: Report
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This report described a pilot study that used scanning electron microscopy to measure the diameters, lengths and calculated masses of airborne asbestos fibres collected on filters at different stages of processing. Samples covered amosite dumped into a hopper at an insulation factory and applied as insulation at an oil refinery, crocidolite dumped into a hopper at an asbestos pipe plant, and chrysotile from the dryer and bagging areas of a Quebec mill and the carding area of a textile plant. Between 200 and 440 fibres were counted per sample. Amosite fibres were shorter during insulation application. Chrysotile fibres had narrower median diameters (0.17, 0.16 and 0.15 um) and fewer fibres longer than 5 um at later stages. In the authors' ranking, fibres thinner than 0.5 um and longer than 5 um made up 17.0 to 18.3 per cent of amosite and crocidolite fibres. Using coil measurements, they made up 1.45 per cent or less of chrysotile fibres. The authors concluded that differences in airborne fibre dimensions between processing stages can be detected. They noted that few samples were examined and that the results require confirmation.

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: Pilot investigation measuring the physical dimensions of airborne asbestos fibres collected on filters, examined by scanning electron microscopy (measurements from photographs)
• Who was studied: Airborne dust samples (not people) from an asbestos textile plant, an asbestos products factory, a local oil refinery, a local store where insulation was applied, and two asbestos mills in Quebec. The chrysotile mill results were based on the plant producing soft fibre. Between 200 and 440 fibres were counted per sample.
• Exposure: Airborne amosite (dumping raw amosite into a hopper at an insulation factory; applying amosite insulation at an oil refinery), crocidolite (dumping from bags into a hopper at an asbestos pipe plant) and chrysotile (mill dryer and bagging areas; carding in a textile plant)
• Main results:
  • Amosite median true fibre diameters were 0.415 um (range 0.076 to 2.978) during dumping and 0.370 um (range 0.076 to 2.922) during application of insulation.
  • Amosite median fibre length was 3.90 um at the manufacturing plant and 2.50 um during insulation application. Fibres longer than 5 um averaged 43.6 per cent at the manufacturing plant and 30.7 per cent during application.
  • Amosite median fibre mass was 2.2 x 10 to the minus 12 grams at the manufacturing plant and 1.0 x 10 to the minus 12 grams during insulation application. The authors suggested that, at the same airborne mass concentration, an insulation worker applying amosite would be exposed to approximately twice as many fibres as a man dumping raw amosite.
  • Percentages of fibres with diameter less than 0.5 um and length greater than 5 um, as ranked by the authors: amosite application of insulation 18.3%, crocidolite 17.5%, amosite dumping 17.0%. For chrysotile (coil length and coil diameter): dryer 1.45%, bagging 1.0%, carding 0.4%.
  • Chrysotile median true diameter was 0.17 um in the dryer samples, 0.16 um in the bagging samples and 0.15 um in the carding samples.
  • Chrysotile fibres longer than 5 um made up 9.4 and 12.9 per cent in the two dryer samples, 4.2 and 5.4 per cent in the bagging area, and 1.6 and 3.0 per cent in the carding area.
  • With total fibre concentrations adjusted to 100 fibres/cc, the authors suggested that exposure to fibres longer than 5 um and thinner than 0.5 um would be considerably greater for amosite and crocidolite workers.
  • The authors suggested that, at the same airborne mass concentration, a person working in a carding area would be exposed to 31 times the number of fibres of a man dumping amosite.
• The authors' conclusion: The authors concluded that differences in the physical parameters of airborne fibres at various stages of processing can be detected, and that on diameter criteria only, chrysotile encountered during carding is potentially the more respirable of the fibres examined.
• Limitations the authors state:
  • The number of samples examined was limited and the results require confirmation.
  • With the limited data, the authors could not conclude that amosite fibre diameters were really reduced by processing.
  • For the chrysotile fibres longer than 5 um and thinner than 0.5 um, the numbers of fibres were too small to assess differences reliably.
  • The crocidolite sample may have been contaminated with a small amount of chrysotile.
  • The videotape method used in an earlier progress report gave inaccurate measurements, so only photograph-based measurements were reported.

Topics

Medical terms in this study, explained in our Lexicon: Scanning Electron Microscopy (SEM), Amosite, Crocidolite, Chrysotile, Carding.

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