Submicroscopic Fibres in Industrial Atmospheres

Our plain-English summary of Submicroscopic Fibres in Industrial Atmospheres, by R.E.G. Rendall, M.I. Skikne (1980).

The study

• Authors: R.E.G. Rendall, M.I. Skikne
• Published: BIOLOGICAL EFFECTS OF MINERAL FIBRES (J.C. WAGNER, EDITOR), LYON: IARC SCIENTIFIC PUBLICATIONS, VOLUME 30, PP. 837-843 (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 industrial hygiene study tested two ways of measuring airborne asbestos fibres longer than 5 micrometres (µm). Most samples came from an amosite mine. Preliminary samples came from a chrysotile mine, an insulation factory, a brake and clutch factory and an asbestos-cement factory. First, the authors weighed dust-laden filters and counted fibres on them to find fibres per milligram of dust. For amosite, the ratios of extreme values to the mean ranged from 0.29 to 1.84. Where more than 10 amosite samples were available, the 95% confidence limits, relative to the mean, ranged from 0.67 to 1.32. Confidence limits for chrysotile were not yet available. Second, they compared a light microscope with electron micrographs of the same area. Among amosite fibres, light microscopy showed 6% of those under 0.2 µm across, 30% of those 0.2 to 0.4 µm across and all of those over 0.5 µm across. The authors suggested that weighing could replace fibre counting, and that combining both techniques could give a quicker routine method. They said factors would need to be derived for each specific area or operation.

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: Industrial hygiene methods study in two parts: (1) comparing the weight of dust collected with fibre counts, to find fibres per mg of dust; (2) comparing light-microscope views with electron micrographs of the same area, to estimate how many fibres longer than 5 µm are too fine to see by light microscope
• Who was studied: Airborne dust samples, mostly from an amosite mine. Preliminary samples came from a chrysotile mine, an insulation factory, a brake and clutch factory and an asbestos-cement factory. A crocidolite mine and UICC reference samples appear in Table 2. Some fibres recovered from lungs were also included. The authors worked at the National Centre for Occupational Health, Johannesburg. The total number of samples cannot be read from the damaged tables.
• Exposure: Airborne asbestos fibres longer than 5 µm (amosite, chrysotile, crocidolite and mixed fibres), measured as fibres per mg of dust and as fibres visible versus not visible by phase-contrast light microscope
• Main results:
  • Amosite fibres less than 0.2 µm in diameter: 6% were visible under the light microscope
  • Amosite fibres 0.2 to 0.4 µm in diameter: 30% were visible under the light microscope
  • Amosite fibres greater than 0.5 µm in diameter: 100% were visible under the light microscope
  • The authors adopted 0.4 µm as the limit of resolution for amosite. Fibres thinner than this were treated as submicroscopic.
  • Fibre content of dust: ratios of extreme values to the mean ranged from 0.29 to 1.84 for amosite and from 0.17 to 2.40 for chrysotile
  • For amosite only, where more than 10 samples were collected, the 95% confidence limits (relative to the mean) ranged from 0.67 to 1.32. No such confidence-limit figures were yet available for chrysotile. The authors said this compared favourably with figures from an earlier study of the same slides read by experienced counters.
• The authors' conclusion: The authors suggested that weighing dust (gravimetric sampling) could replace the laborious fibre-counting procedures. They also suggested that combining it with correction factors for submicroscopic fibres could give a quicker routine method and a truer record of fibre concentration.
• Limitations the authors state:
  • Confidence limits were not yet available for chrysotile
  • Results from industries other than the amosite mine, and from fibres recovered from lungs, were preliminary
  • Factors and ratios would need to be derived for each specific area or operation

Topics

Medical terms in this study, explained in our Lexicon: Industrial Hygiene, Amosite, Chrysotile, Asbestos-Cement.

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