The counting of small numbers of asbestos fibres on membrane filters: a comparison of results from some commercial laboratories

Our plain-English summary of The counting of small numbers of asbestos fibres on membrane filters: a comparison of results from some commercial laboratories, by M.J. Duggan, E.W. Culley (The Annals of Occupational Hygiene, 1978).

The study

• Authors: M.J. Duggan, E.W. Culley
• Journal: The Annals of Occupational Hygiene
• Published: 1978;21(1):85-9
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This short communication from the Greater London Council's Environmental Sciences Group compared how commercial laboratories counted the small numbers of asbestos fibres expected in ordinary air. On six consecutive working days the authors took nine simultaneous air samples in their own laboratory and office area at County Hall, London. Each sample passed 1 cubic metre of air through a membrane filter. One sample from each day went to each of eight laboratories offering fibre counting by phase-contrast microscopy, and one set was kept for the authors' own count. The filter area examined ranged from about 0.08 to 48 square millimetres, and standard errors ranged from about 15 to 100%. The largest disagreement in reported fibre concentration was 100 to 1, between laboratories A and E for batch 3. Some laboratories said they counted only asbestos fibres and others all fibres. Only one laboratory reported standard errors or confidence limits. The authors concluded that reliable results were evidently not possible at the fibre concentrations likely in the urban environment, and that the discrepancies cast doubt on results at much higher concentrations.

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: Inter-laboratory comparison of fibre counts on matched air-sample filters (short communication)
• Who was studied: Air samples, not people: nine simultaneous samples on each of six consecutive working days, taken in the authors' laboratory and office area at County Hall, London. They were split into nine batches of six, with eight batches sent to commercial laboratories and one kept by the authors.
• Exposure: Airborne fibres in indoor office and laboratory air, sampled for about 6 hours to collect 1 cubic metre of air per membrane filter (Millipore type AA, 37 mm) and counted by phase-contrast microscopy. No fibre type was named.
• Main results:
  • Across the laboratories, the area of filter examined ranged from about 0.08 to 48 square millimetres.
  • Standard errors of the reported results ranged from about 15 to 100%.
  • The greatest discrepancy in reported total fibres (fibre concentration) was 100 to 1, for batch 3 between laboratories A and E (the table shows 110 for A and 11000 for E).
  • Laboratory G, which counted only asbestos fibres, consistently reported higher counts than laboratories H and I, which counted all fibres. The confidence limits on laboratory G's results were very large.
  • Only one laboratory reported standard errors or confidence limits.
  • Two laboratories made arithmetical mistakes in their total fibre figures, one by a factor of 10 and one by a factor of 3.
• The authors' conclusion: The authors concluded that it was evidently not possible to obtain reliable results at fibre concentrations of the order likely in the urban environment. They added that the size of the discrepancies cast doubt on results that would be obtained at much higher concentrations.
• Limitations the authors state:
  • The authors could not account for the discrepancies with certainty. Repeating each count in the presence of an experienced counter was not practicable.
  • Only a sample of the many UK commercial laboratories was tested. The authors presumed a larger sample would give an even wider range of results.
  • The laboratories were not asked to follow the Asbestosis Research Council working procedures in detail.
  • The gross deposit of other particulate matter on the filter can mask fibres, which limits how much air can be sampled.

Related studies

• 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)
• The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method — A.M. Johnston, A.D. Jones, et al. (1982)
• A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy — J.R. Hoyes, R. Clayton (1980)
• In situ identification of asbestos fibres collected on membrane filters for counting — N.P. Vaughan, S.J. Rooker, et al. (1981)
• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)

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