Inter-laboratory comparisons of the counting of asbestos fibres sampled on membrane filters

Our plain-English summary of Inter-laboratory comparisons of the counting of asbestos fibres sampled on membrane filters, by S.T. Beckett, M.D. Attfield (The Annals of Occupational Hygiene, 1974).

The study

• Authors: S.T. Beckett, M.D. Attfield
• Journal: The Annals of Occupational Hygiene
• Published: 1974;17(2):85-96
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This was a methods study, not a health study. It tested how consistently British laboratories counted asbestos fibres on slide-mounted membrane-filter samples. The first exchange used eleven slides of chrysotile, amosite and crocidolite. Before any contact, four laboratories new to asbestos counting, working from the written instructions, got about half the counts of two standard laboratories for factory samples and about one quarter for UICC chrysotile. An experienced laboratory with no outside contact was as far from the standard as the novices. After personal instruction, agreement was good for industrial slides, and the authors reported "a greatly improved agreement (67 per cent)" for UICC chrysotile. In a second exchange among five experienced laboratories, counting only inside the eyepiece graticule grid gave about three times the full-field count for chrysotile and 1.57 times for amosite. Using their usual methods, laboratories counted from 0.57 to 1.95 times the average for chrysotile and from 0.83 to 1.23 times for amosite. The authors concluded that counting procedures needed closer definition and standardisation. They described the trial as relatively small-scale.

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: Two inter-laboratory slide exchange trials comparing asbestos fibre counts (a methods and quality-comparison study)
• Who was studied: Trial 1 had four laboratories experienced with non-fibrous mineral dusts but not asbestos (A to D), one experienced but isolated asbestos laboratory (E), and two standard laboratories (F, G). Trial 2 had five experienced laboratories: F, G, H and K in the chrysotile exchange and G, J and K in the amosite exchange.
• Exposure: Slides of chrysotile (UICC standard reference samples and samples from an asbestos textile factory), amosite (from an asbestos cement factory) and crocidolite (from removal of lagging). Trial 1 densities were 2 x 10^3 to 112 x 10^3 fibres/cm2.
• Main results:
  • Trial 1, before contact: the inexperienced laboratories counted about half the standard for factory samples and about one quarter for UICC chrysotile.
  • Trial 1: the experienced laboratory without outside contact (E) was as far from the standard values as the novices.
  • Trial 1, after personal instruction: agreement was good for industrial slides, with a greatly improved agreement (67 per cent) for UICC chrysotile.
  • In one case only one fifth of the fibres were counted, because only one focal plane had been scanned.
  • Trial 2, chrysotile: the grid method gave counts about three times the full-field counts (T = 3.0; 2.9 excluding UICC chrysotile).
  • Trial 2, amosite: the grid to full-field ratio was smaller, 1.57.
  • When laboratory J recounted three amosite slides by the grid method that it had earlier counted full field, its count increased 1.5 times.
  • Using their normal methods, the experienced laboratories' lowest and highest ratios to the mean were 0.57 and 1.95 for chrysotile (0.68 and 1.62 excluding UICC) and 0.83 and 1.23 for amosite.
  • If all laboratories used the same method, the estimated spread would be 0.67 to 1.35 for chrysotile (0.68 to 1.32 excluding UICC) and 0.91 to 1.14 for amosite.
  • Repeat counts by originating laboratories showed no evidence of a systematic change over the trial (no evidence of slide deterioration).
• The authors' conclusion: The authors concluded that there is a need for closer definition and standardisation of counting procedures.
• Limitations the authors state:
  • The authors described the trial as relatively small-scale.
  • The grid versus full-field difference may have been accentuated by the wide range of slide densities, and is unlikely to be the same with other samples and microscope optical systems.
  • Effects of other counting methods and microscope factors could not be separated from the laboratory (reader) effect.
  • In Trial 1, the effect of grid versus full-field counting could not be analysed because it was masked by the large variation from inexperience.
  • The grid to full-field ratio may differ between counters, but the design did not allow it to be estimated separately for each.

Related studies

• 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 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)
• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)
• Comparison of a fibrous aerosol monitor (FAM) with the membrane filter method for measuring airborne asbestos concentrations — P.J. Iles, T. Shenton-Taylor (1986)
• 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 comparison of impinger and membrane filter techniques for evaluating air samples in asbestos plants — H.E. Ayer, J.R. Lynch, et al. (1965)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.