Size and shape of airborne asbestos fibres in mines and mills

Our plain-English summary of Size and shape of airborne asbestos fibres in mines and mills, by C.Y. Hwang (British Journal of Industrial Medicine, 1983).

The study

• Author: C.Y. Hwang
• Journal: British Journal of Industrial Medicine
• Published: 1983;40(3):273-9
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

There is increasing evidence that fibre size and shape play an important part in the production of health effects related to asbestos. The dimensions of airborne fibres collected at various stages of fibre processing in three mines and six mills producing three types of asbestos were measured using phase contrast light microscopy and transmission electron microscopy. Airborne fibres of different asbestos types had appreciably different size and shape distributions. For a given asbestos type, fibres collected at different stages of processing differed in their size distributions but the differences were considerably less than between fibre types. Most of the airborne fibres to which miners and millers were exposed were short and thin and thus respirable. The physical properties which best differentiated crocidolite fibres from other types of asbestos and which had higher values determined for crocidolite fibres than those obtained for the other types, were median aspect ratio and the proportion of long thin fibres--that is, fibres less than or equal to 0.2 micron in diameter and greater than 5 micron in length as the percentage of total fibres. The median true diameter of amosite fibres was about four and three times higher than the median true diameters of chrysotile and crocidolite fibers respectively. The median true length of amosite fibres was more than four and two times higher than the median true lengths of chrysotile and crocidolite fibres respectively. The observed differences in size and shape of airborne fibres have important implications for the setting of work environmental standards and in explaining differences in health risks associated with different types of fibre.

In plain English

This study measured the size and shape of asbestos fibres in workplace air. It did not examine disease in workers. Air samples came from a crocidolite mine and two mills in Cape Province, South Africa, an amosite mine and three mills in Transvaal, South Africa, and a chrysotile open pit mine and mill in Quebec, Canada. Fibres from mining and from the final bagging stage were measured by light and electron microscopy. Chrysotile fibres were thinnest (median diameter 0.05 to 0.06 micrometres) and amosite thickest (0.20 to 0.26). Median lengths in the mines were 0.95 micrometres for crocidolite, 1.83 for amosite and 0.34 for chrysotile. Differences between processing stages were smaller than differences between fibre types, and most fibres were short and thin. Crocidolite had the highest median aspect ratio (length divided by width) and the highest share of long thin fibres. The author concluded that these differences have implications for workplace standards and for explaining different health risks between fibre types.

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 measurement study of airborne fibre dimensions (no health outcomes studied)
• Who was studied: Airborne dust samples from an underground crocidolite mine and two mills (Cape Province, South Africa), an underground amosite mine and three mills (Transvaal, South Africa), and a chrysotile open pit mine and mill (Quebec, Canada). Fibres measured by electron microscopy: crocidolite 2779 initial stage and 1811 final stage; amosite 802 and 2662; chrysotile 2269 and 3047. Sampling dates not given.
• Exposure: Airborne crocidolite, amosite and chrysotile fibres at the initial processing stage (mining operations such as drilling, shovelling, slushing, hammering and tipping) and the final stage (bagging). Particles with aspect ratio of three or more counted as fibres; bundles counted as one fibre.
• Main results:
  • Median true diameter by electron microscopy: crocidolite 0.07 µm (initial) to 0.09 µm (final); amosite 0.20 to 0.26 µm; chrysotile 0.05 to 0.06 µm. Chrysotile fibres were thinnest and amosite thickest.
  • Fibres wider than 0.25 µm were 55.4% of fibres in amosite bagging areas (highest) and 3.4% in chrysotile (or crocidolite) mining areas (lowest). No airborne fibres were wider than 3 µm.
  • Median lengths in the mine: crocidolite 0.95, amosite 1.83 and chrysotile 0.34 µm. In bagging areas: 1.16, 2.53 and 0.55 µm respectively.
  • Fibres longer than 5 µm were 24.5% of fibres in amosite bagging areas (highest) and 1.3% in chrysotile mining areas (lowest).
  • Differences between processing stages were considerably smaller than differences between fibre types.
  • Median aspect ratio at the initial stage: crocidolite 11.7, amosite 8.4, chrysotile 6.3. At the final stage: 13.2, 8.8 and 8.0. Fibres with aspect ratio over 40 at the initial stage: 9.6%, 2.9% and 2.5%. At the final stage: 11.5%, 5.1% and 4.7%. Crocidolite was highest at both stages.
  • Fibres longer than 5 µm and 0.2 µm or less in diameter, as a percentage of all fibres: mining, crocidolite 3.02, amosite 2.23, chrysotile 0.34. Bagging, 5.25, 3.65 and 2.09.
  • Most airborne fibres that miners and millers were exposed to were short and thin, and therefore respirable.
• The authors' conclusion: The author concluded that the observed differences in fibre size and shape have implications for setting workplace standards and for explaining differences in health risks between fibre types. The author suggested that if fibre dimensions matter for mesothelioma, aspect ratio and the share of long thin fibres could be the most significant properties.
• Limitations the authors state:
  • Measuring the complete length distribution of airborne fibres was difficult because of the electron microscope specimen grids. Light and electron microscopy results were combined to estimate it.
  • Many chrysotile bundles in the mill were long and curly, and their dimensions were difficult to measure.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite, Chrysotile, Crocidolite.

Medical terms in this study, explained in our Lexicon: Transmission Electron Microscopy (TEM), Crocidolite, Aspect Ratio (Length-to-diameter ratio), Amosite, Chrysotile.

Related studies

• Variation in fibre and dust counts in an asbestos mine and mill — R.C. Parsons, D.G. Bryant, et al. (1986)
• Relationships between simultaneous airborne dust samples taken with five types of instruments at South African asbestos mines and mills — R.S. Du Toit, L.W. Isserow, et al. (1983)
• The sizes, shapes, and mineralogy of asbestos structures that induce lung tumors or mesothelioma in AF/HAN rats following inhalation — D.W. Berman, K.S. Crump, et al. (1995)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• Size distributions of occupational airborne asbestos textile fibres as determined by transmission electron microscopy — A.P. Rood, R.R. Streeter (1984)
• Late progression of radiographic changes in Canari chrysotile mine and mill exworkers — J.R. Viallat, C. Boutin, et al. (1983)

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