Physical Parameters Of Airborne Asbestos Fibres In Various Work Environments: Preliminary Findings

Our plain-English summary of Physical Parameters Of Airborne Asbestos Fibres In Various Work Environments: Preliminary Findings, by G.W. Gibbs, C.Y. Hwang (1975).

The study

• Authors: G.W. Gibbs, C.Y. Hwang
• Published: American Industrial Hygiene Association Journal 36(6):459-466, June (1975)
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library, J-M no. 004955. The article is still under copyright, so we describe it here rather than post it.

In plain English

This pilot study measured the size and shape of asbestos fibres in workplace air. Two air samples were taken at each of four kinds of location: the carding machine of a textile plant that used only chrysotile; an asbestos products plant where bags of amosite and crocidolite were emptied into hoppers; an oil refinery where insulation containing mainly amosite was applied; and the dryer and bagging areas of a chrysotile mill. Fibres were examined by scanning electron microscopy. Airborne amosite tended to be finer and shorter during insulation work than during bag emptying. Chrysotile fibres tended to be smaller at later processing stages and were longest in the dryer area. The authors also estimated what share of each sample's fibres optical counting would detect, assuming it sees only fibres thicker than 0.5 micrometres and longer than 5 micrometres. On that basis, a considerably larger share of the amosite fibres would be detected than of the chrysotile or crocidolite fibres. They calculated that, for the same airborne mass, carding workers would be exposed to about 30 times as many fibres as a worker dumping amosite. The authors stressed their data were limited. They concluded that their results supported animal work suggesting asbestosis is related to the mass of dust inhaled, and mesothelial tumours to fibres in a specific range of diameters and lengths.

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 airborne asbestos fibres on air-sample filters by scanning electron microscopy
• Who was studied: Air samples, two from each location: the carding machine of an asbestos textile plant, the bag-emptying (dumping) operation at an asbestos products plant, insulation application at a local oil refinery, and the dryer and bagging areas of a chrysotile mill. The authors were based in Montreal. The readable text does not give the sampling dates or the number of fibres measured.
• Exposure: Airborne chrysotile (textile carding, mill dryer and bagging), amosite and crocidolite (emptying of bags into hoppers), and insulation materials containing mainly amosite (application at an oil refinery)
• Main results:
  • Airborne amosite tended to be finer during the application of insulation than during the dumping of raw amosite
  • Insulation workers were exposed to shorter amosite fibres than workers in the manufacturing plant
  • The median true diameter of crocidolite fibres during dumping was 0.248 micrometres
  • For chrysotile, the percentage of fibres with a diameter of 0.5 micrometres or less was 67 in the dryer area, 82 in the bagging area and 88 in the carding area
  • Chrysotile fibres in the mill dryer area were longer than those in the bagging and carding areas
  • The median length of crocidolite fibres during dumping was 2.50 micrometres
  • The median aspect ratio (length to diameter) for crocidolite was 9.7, slightly greater than for amosite
  • For crocidolite, 17.5% of fibres had diameters less than 0.5 micrometres and lengths greater than 5 micrometres
  • The proportion of chrysotile fibres thinner than 0.5 micrometres and longer than 5 micrometres decreased from the dryer through to the carding operation
  • The authors assumed that optical counting detects only fibres more than 0.5 micrometres in diameter and more than 5 micrometres long, and estimated on that basis the percentage of each sample's total fibre count that would be observed. A considerably larger percentage of the amosite fibres would be observed optically than of the chrysotile or crocidolite fibres.
  • Total fibre concentrations varied and were generally highest in the carding area
  • The authors calculated that, for the same airborne mass concentration, a worker on a chrysotile textile carding machine would be exposed to about 30 times the number of fibres of a man dumping amosite
  • On fibre diameter alone, the authors judged chrysotile encountered during carding to be potentially more respirable than the other fibres examined
• The authors' conclusion: The authors concluded that their results so far supported experimental work on animals suggesting that asbestosis is related to the mass of airborne dust inhaled, and that primary malignant mesothelial tumours are related to exposure to fibres in a specific range of diameters and lengths. They also concluded that measuring the physical parameters of fibres in various industries is feasible.
• Limitations the authors state:
  • The inferences were based on limited data and might not be supported by more extensive measurement
  • The number of samples examined was small and the results require confirmation
  • Too few chrysotile fibres were examined for differences between the dryer, bagging and carding areas to be reliably assessed
  • Mass was calculated assuming circular fibre cross-sections, which was not strictly valid for amosite, whose cross-section is rectangular

Topics

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

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