In situ identification of asbestos fibres collected on membrane filters for counting

Our plain-English summary of In situ identification of asbestos fibres collected on membrane filters for counting, by N.P. Vaughan, S.J. Rooker, J.M. Le Guen (The Annals of Occupational Hygiene, 1981).

The study

• Authors: N.P. Vaughan, S.J. Rooker, J.M. Le Guen
• Journal: The Annals of Occupational Hygiene
• Published: 1981;24(3):281-90
• Read it: PubMed · Publisher

In plain English

This laboratory methods paper from the UK Health and Safety Executive described counting and identifying asbestos fibres on the same air-sampling membrane filter. The standard method gave only a total respirable fibre count, with no distinction between asbestos types. British standards were stricter for crocidolite, and different limits had been proposed for amosite and chrysotile. Three commercial filter types were cleared with solvent and oven-dried, collapsing them to about 15% of their original thickness. They were then etched in an oxygen plasma to expose the fibres. Fibres could then be counted by phase contrast microscopy and identified by polarised light microscopy, and two filter types also suited scanning electron microscopy. Polarisation colours could be readily determined in fibres down to 0.8 micrometres in diameter for amosite, 1.25 for crocidolite and 1.5 for chrysotile, though considerably thinner fibres could often be identified. A colour-change (pleochroism) test, applicable only to crocidolite, worked down to 0.6 micrometres. The authors concluded the method was an alternative to the standard technique when identification was needed, not a replacement, and noted it would likely take longer.

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: laboratory methods-development paper (microscopy sample preparation and fibre identification technique)
• Who was studied: No people were studied. The work used three commercial membrane filter types (Millipore MF, Millipore Celotate, Gelman DM) and samples of various asbestos types, at the Health and Safety Executive laboratories in London. The number of samples is not stated.
• Exposure: Asbestos fibre types on filters: mainly amosite, crocidolite and chrysotile. Tremolite, anthophyllite and actinolite were also covered in the identification procedure and tables.
• Main results:
  • The standard membrane filter technique allowed only a total respirable fibre count and could not distinguish asbestos types. British standards were more restrictive for crocidolite, and different control limits had been proposed for amosite and chrysotile.
  • After clearing, the filters collapsed to about 15% of their original thickness, forming a transparent plastic film.
  • The authors' abstract gives lower fibre diameter limits for identification by polarised light microscopy of 0.8 micrometres for amosite, 1.5 for chrysotile and 1.25 for crocidolite.
  • These figures (Table 4) are the minimum diameters at which polarisation colours could be readily determined. The authors state that considerably thinner fibres can often be identified.
  • The pleochroism test, which applies only to crocidolite, was sensitive down to fibre diameters of 0.6 micrometres.
  • Celotate and DM filters could also be examined by scanning electron microscopy with energy dispersive X-ray analysis.
• The authors' conclusion: The authors concluded that the technique allows identification of the three commonest asbestos types, fibre counting and, for some filter types, SEM examination, all on the same filter. They presented it as an alternative to the standard membrane filter technique when identification is required, not necessarily a replacement.
• Limitations the authors state:
  • The new preparation method is likely to take longer than the standard one.
  • Optical identification works only for the larger fibres. Finer fibres require scanning electron microscopy.
  • The identification techniques give only rough percentages of the different asbestos types in a mixed sample.

Related studies

• Clearing and mounting techniques for the evaluation of asbestos fibres by the membrane filter method — J.M. Le Guen, S. Galvin (1981)
• The counting of small numbers of asbestos fibres on membrane filters: a comparison of results from some commercial laboratories — M.J. Duggan, E.W. Culley (1978)
• Inter-laboratory comparisons of the counting of asbestos fibres sampled on membrane filters — S.T. Beckett, M.D. Attfield (1974)
• A comparison of fibre counting stopping rules in the application of the membrane filter method — N.P. Crawford, W.M. Maclaren, et al. (1987)
• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)
• A procedure for the estimation of asbestos collected on membrane filters using transmission electron microscopy (TEM) — A.P. Middleton, E.A. Jackson (1982)

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