A summary of asbestos fibre counting experience in seven countries

Our plain-English summary of A summary of asbestos fibre counting experience in seven countries, by G.W. Gibbs, P. Baron, S.T. Beckett, et al (The Annals of Occupational Hygiene, 1977).

The study

• Authors: G.W. Gibbs, P. Baron, S.T. Beckett, R. Dillen, R.S. du Toit, M. Koponen, K. Robock
• Journal: The Annals of Occupational Hygiene
• Published: 1977;20(4):321-32
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The membrane filter method for the evaluation of airborne concentrations of asbestos in the work place, is now used in many countries. In order to ensure uniform protection for the worker and internationally comparable exposure data it is important that different laboratories can reproduce fibre counts with reasonable accuracy. The results of an international counting trial of fibre by centres in nine countries were published recently in this journal. This current report summarises the results of internal exchanges of membrane filters for asbestos counting in seven of these countries. Observations from these several countries indicate the need for regular comparisons of counts between laboratories, regular contact with experienced observers, proper training in the use of the phase contrast microscope, standardisation of the methods of counting agglomerates, attention to the types of samples used for internal and external comparisons, choice of microscope, and separate training for counting chrysotile and amphibole fibres. An improved method of producing standard asbestos samples for counting purposes is required.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This report summarised exchanges of membrane filter samples for counting airborne asbestos fibres between laboratories and observers within seven countries: Belgium, Canada, Finland, Germany, South Africa, the United Kingdom and the United States. Fibres of chrysotile, amosite or crocidolite were counted by phase contrast microscopy. No health outcomes were studied. Two Belgian laboratories had median count ratios of 0.98 for chrysotile and 0.91 for amphibole samples. In Canada, where only nine of 15 laboratories had completed the exchange, agreement on individual samples was poor. Two German laboratories generally agreed within plus or minus 30%. In South Africa, chrysotile count ratios between laboratories ranged from 0.25 to 14.2, while amosite counts generally agreed well. In the United Kingdom, inexperienced laboratories agreed much better after contact with experienced observers. In the United States testing programme, coefficients of variation for most sample counts ranged from 0.35 to 0.70. The authors concluded that differences between counters on a single sample can be extremely large, but that laboratories in close contact that regularly exchange samples can achieve much better agreement. Some of the trials were still incomplete.

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: Summary report of interlaboratory and inter-observer comparison (exchange) trials of asbestos fibre counting by the membrane filter method. It is a methods study, not a health study.
• Who was studied: Fibre-counting laboratories and observers within seven countries (Belgium, Canada, Finland, Germany, South Africa, United Kingdom, United States). Between 2 and 15 laboratories or counters took part per exchange. The work followed a 1974-1975 international exchange.
• Exposure: No human exposure was studied. The material was membrane filter samples of airborne dust containing chrysotile, amosite or crocidolite, collected from sources including artificial dust clouds, textile plants, and mining and milling. Fibres were counted by phase contrast microscopy.
• Main results:
  • Belgium, two laboratories: chrysotile count ratios ranged from 0.49 to 2.54 (median 0.98). Amphibole count ratios ranged from 0.63 to 1.68 (median 0.91).
  • Canada: only nine of 15 laboratories had completed the exchange, and agreement on individual samples was poor.
  • Finland: no systematic difference was found between the two observers. The geometric mean ratio of observer A to observer B over 40 slides was 0.97.
  • Germany, two laboratories: agreement on the chrysotile samples was generally within plus or minus 30%.
  • South Africa, three laboratories: agreement on chrysotile was poor, with count ratios from 0.25 to 14.2. Agreement on amosite samples was generally good.
  • South Africa, same three laboratories, amosite samples: there was generally good agreement between the laboratories.
  • United Kingdom: agreement of inexperienced laboratories improved considerably after contact with experienced observers. An experienced laboratory without contact with other counters performed as poorly as the novices.
  • United Kingdom: using a graticule grid with an area of less than one tenth of the full field gave significantly higher counts.
  • United States, NIOSH Proficiency Analytical Testing programme: the coefficient of variation for most sample counts ranged from 0.35 to 0.70.
  • United States: the US counter in the international trial produced results high compared with the average of all countries, by a ratio of 1.81 to 1.
• The authors' conclusion: The authors concluded that differences between counters on a single sample can be extremely large. They also concluded that laboratories in close contact with regular sample exchanges can achieve much better agreement. They called for regular exchanges, contact with experienced observers, microscope training, and standardisation of counting methods.
• Limitations the authors state:
  • Some of the trials were still incomplete, and detailed results were to be published separately by each country.
  • In Canada, only nine of the 15 participating laboratories had completed the exchange at the time of reporting.
  • Methods of dust collection were not examined in these studies.

Topics

Medical terms in this study, explained in our Lexicon: Membrane Filter Method, Chrysotile, Amphibole Group.

Related studies

• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• 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)
• A comparison of fibre counting across three European national proficiency testing schemes — A.D. Jones, M.C. Arroyo, et al. (2005)
• Proposal to adapt the WASP programme to fibre counting tests — M. Grzebyk, E. Kauffer, et al. (2006)
• Simultaneous airborne dust samples with konimeter, thermal precipitator and dosimeter in asbestos mines — R.S. du Toit, T.C. Gilfillan (1977)

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