Dimensions of Airborne Asbestos Fibres

Our plain-English summary of Dimensions of Airborne Asbestos Fibres, by G.W. Gibbs, C.Y. Hwang (1980).

The study

• Authors: G.W. Gibbs, C.Y. Hwang
• Published: BIOLOGICAL EFFECTS OF MINERAL FIBRES (J.C. WAGNER, EDITOR), LYON: IARC SCIENTIFIC PUBLICATIONS, VOLUME 30., PP 69-78 (1980)
• Type of article: Conference paper
• 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 study measured the size of airborne asbestos fibres in mines and mills that each handled one fibre type: crocidolite (Cape Province, South Africa), amosite (Transvaal, South Africa) and chrysotile (Quebec, Canada). Dust samples were examined with light and electron microscopes. Median fibre lengths in the mines were 0.95 µm for crocidolite, 1.83 µm for amosite and 0.34 µm for chrysotile. In bagging areas they were 1.16, 2.53 and 0.55 µm. Median diameters were 0.05-0.06 µm for chrysotile, 0.07-0.09 µm for crocidolite and 0.20-0.26 µm for amosite. No airborne fibre was wider than 3 µm. Median individual-fibre mass was highest for amosite, so the authors stated that the same airborne mass would contain fewer amosite fibres. Assuming that phase-contrast microscopy sees fibres longer than 5 µm and wider than 0.3 µm, the authors calculated that during bagging such fibres would make up only 0.6% of crocidolite, 16.9% of amosite and 1.6% of chrysotile fibres. The authors concluded that most fibres workers were exposed to were short and narrow, and that the counting method strongly affects what is seen.

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: Measurement study of the dimensions of airborne asbestos fibres. Air samples were taken on membrane filters and examined by light optical, transmission electron and scanning electron microscopy. This was not a study of disease.
• Who was studied: Airborne dust samples from working areas of mines and mills producing crocidolite (Cape Province, South Africa), amosite (Transvaal, South Africa) and chrysotile (Quebec, Canada). The number of samples and the sampling dates are not stated.
• Exposure: Airborne crocidolite, amosite and chrysotile in mining and in milling (bagging) areas, each in processes where only one fibre type was present. Fibres were defined as particles with a length-to-diameter ratio greater than 3 to 1.
• Main results:
  • Median fibre lengths in the mine were 0.95 µm for crocidolite, 1.83 µm for amosite and 0.34 µm for chrysotile. In the bagging area they were 1.16, 2.53 and 0.55 µm, respectively.
  • Processing tended to reduce the proportion of shorter airborne fibres for all fibre types, especially for amosite.
  • Across mining and bagging, median true diameters ranged from 0.05-0.06 µm for chrysotile and from 0.07-0.09 µm for crocidolite.
  • Amosite had a flatter, apparently multimodal diameter distribution, with median diameters of 0.20-0.26 µm depending on the process.
  • No airborne fibres had a diameter greater than 3 µm. The authors stated that, on this basis, all of them would be capable of reaching the pulmonary alveoli.
  • Median masses of individual fibres in mining were 0.0143 for crocidolite, 0.1956 for amosite and 0.0018 for chrysotile. The unit is illegible in the scan.
  • For a given airborne mass, there would be considerably fewer amosite fibres than crocidolite or chrysotile fibres.
  • Most crocidolite fibres (34.09% in mining and 26.90% in bagging) and chrysotile fibres (60.73% and 51.65%) fell in the class of lengths under 2.5 µm and diameters under 0.06 µm.
  • The authors assumed phase-contrast microscopy sees fibres longer than 5 µm and wider than 0.3 µm. On that assumption, such fibres would be 0.6% of all airborne fibres during crocidolite bagging, 16.9% for amosite and 1.6% for chrysotile.
  • In the same calculation, an optical count of 2 fibres/ml would correspond to total fibre concentrations of 351 f/ml for crocidolite, 12 f/ml for amosite and 126 f/ml for chrysotile.
  • Median coil diameters were about twice the true diameters. Coil and true lengths of chrysotile were similar. The authors suggested that curliness is not a major factor in explaining differences in lung penetration between amphibole and chrysotile fibres.
• The authors' conclusion: The authors concluded the following:
• Most fibres to which workers are exposed are short and narrow.
• Differences in fibre dimensions between processes are smaller than differences between fibre types.
• Light and transmission electron microscopy must be combined, probably with scanning methods as well, to describe the full size distribution.
• Further analysis is needed to judge whether differences in fibre dimensions help explain differences in health risks, especially for mesothelioma.
• Limitations the authors state:
  • The observation about curliness applies only to fibres seen by transmission electron microscopy.
  • Scanning electron microscopy of crocidolite indicated that transmission electron microscopy may underestimate the number of fibres under 0.2 µm in diameter, because grid margins restrict length measurements. The authors stated this does not affect their comparisons.
  • Transmission electron microscopic methods can lead to under-reporting of long fibres.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Cape Province, Amosite, Transvaal, Chrysotile.

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