Confusion about the precision of asbestos fibres counting by electron microscopy

Our plain-English summary of Confusion about the precision of asbestos fibres counting by electron microscopy, by B. Préat (The Annals of Occupational Hygiene, 2000).

The study

• Author: B. Préat
• Journal: The Annals of Occupational Hygiene
• Published: 2000;44(1):75-6
• Type of article: Letter
• Read it: PubMed · Publisher

In plain English

This letter to the editor reported no new measurements, workers or health outcomes. The author discussed how scanning and transmission electron microscopy methods (German VDI 3492 Part I; ISO/DIS 10312 and ISO/DIS 13794) state the precision of airborne asbestos fibre counts. The author argued that these electron microscopy standards base their 95% confidence interval only on Poisson limits around the counted number. Because that distribution is skewed, the author wrote, this interval describes counts scattered around a mean, not the true concentration estimated from one measurement. The author therefore called the electron microscopy standards' wording misleading. Germany's TRGS 519 requires, for clearance testing, that this interval's upper limit be below 1000 f/m3. The author argued that meeting this rule does not show with 95% confidence that the true concentration is not above 1000 f/m3. Most phase contrast optical microscopy methods, the author noted, avoid this error. Lacking a suitable table, the author wrote, compliance could only be checked with 95% confidence by comparing the counted fibres with the table's upper limit (inspectorate's assessment) or lower limit (employer's strategy) for the fibre number matching the limit value.

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: letter to the editor (opinion and methods commentary; no new data)
• Who was studied: No people were studied. The letter discusses asbestos fibre counting standards: German VDI 3492 Part I, ISO/DIS 10312 and ISO/DIS 13794.
• Exposure: Counting of airborne asbestos fibres on filters by phase contrast optical microscopy compared with scanning or transmission electron microscopy; no fibre type is specified
• Main results:
  • The author argued that the interval tabled in the electron microscopy standards gives the spread of measurements about the mean, not the confidence interval of the existing concentration based on a single measurement.
  • According to the author, the interval in the electron microscopy methods can only be used as an indicator of the error of the counting process.
  • The author argued that the German TRGS 519 clearance rule (upper limit of the 95% "confidence interval" below 1000 f/m3) does not allow asserting with 95% confidence that the existing concentration is not higher than 1000 f/m3.
  • The author stated that most phase contrast optical microscopy methods (HSE 1995, NIOSH 1994, WHO 1997) avoid this problem and give the confidence interval of the estimated existing concentration.
• The authors' conclusion: The author concluded that, lacking a suitable table, the only way to check compliance with 95% confidence under the electron microscopy standards has three steps. First, calculate the fibre number corresponding to the limit value. Second, take from the standards' table either the upper limit (inspectorate's assessment) or the lower limit (employer's strategy). Third, compare that limit with the counted fibres.

Related studies

• Performance of asbestos fibre counting laboratories by transmission electron microscopy — B. Préat (2001)
• The use of a new static device based on the collection of the thoracic fraction for the assessment of the airborne concentration of asbestos fibres by transmission electron microscopy — E. Kauffer, J.C. Vigneron, et al. (1996)
• An electron microscopy study of the effect of asbestos dust on the lung — J.M. Davis (1963)
• Electron microscopy: a brief history and review of current clinical application — R.E. Gordon (2014)
• Electron microscopy remains the gold standard for the diagnosis of epithelial malignant mesothelioma: a case study — E.A. Oczypok, T.D. Oury (2015)
• The utility of electron microscopy in detecting asbestos fibers and particles in BALF in diffuse lung diseases — T. Kido, Y. Morimoto, et al. (2017)

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