Industrial trials with the Vickers M88 rapid asbestos fibre counter

Our plain-English summary of Industrial trials with the Vickers M88 rapid asbestos fibre counter, by A.D. Jones, R.W. Gale (The Annals of Occupational Hygiene, 1982).

The study

• Authors: A.D. Jones, R.W. Gale
• Journal: The Annals of Occupational Hygiene
• Published: 1982;25(1):39-51
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This study tested a prototype Vickers M88 asbestos fibre counter, which magnetically aligns fibres on air-sample filters and measures scattered light. Five laboratories used samples from asbestos textile, brake lining and friction product, asbestos cement and insulation factories; all contained chrysotile, and one also some amphibole. The authors compared M88 readings with visual microscope counts of the same aligned samples. For aligned textile samples, excluding four weaving and six M88-rejected dusty samples, visual count equalled 0.33 times the M88 evaluation (95% confidence limits plus or minus 0.05). For brake lining and friction product samples (one talc-dust sample excluded), the factor was 0.08 plus or minus 0.02, becoming 0.11 plus or minus 0.03 after allowing for mounting differences. Asbestos cement and insulation results were inconclusive: fibre densities were very low and the products' materials differed substantially. M88 results from different laboratories agreed well. Participants expected about 50 samples a day per operator with production equipment. The authors concluded the M88 compared favourably with visual counters for consistency, reliability and speed, but that a calibration should not be assumed to apply elsewhere.

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: Multi-laboratory industrial trial comparing a prototype instrument (the Vickers M88 rapid asbestos fibre counter) with visual microscope counting of fibres on membrane filter samples; not a health study
• Who was studied: Membrane filter air samples: 20 matched (duplicate) pairs supplied by each of four organizations, TBA (Turner Brothers Asbestos), TAC (Turner Asbestos Cement), Ferodo and BBA (British Belting and Asbestos). Samples were prepared and evaluated at five laboratories: TBA, TAC, Ferodo, the Institute of Occupational Medicine (IOM) and Vickers Instruments (VI). Dates of sampling are not given.
• Exposure: Airborne dust from the manufacture of brake linings and friction products, asbestos cement, insulation products and asbestos textiles. All samples contained chrysotile; one asbestos cement sample also contained some amphibole asbestos.
• Main results:
  • For all aligned textile samples combined (TBA and BBA), the relationship was visual count = (0.33 plus or minus 0.05) x (M88 evaluation), with 95% confidence limits. Four weaving samples were excluded, and six BBA samples rejected by the M88 were also not included. The regression explained a proportion of 0.89 of the total variation.
  • Six of the 15 BBA carding samples were so dusty that the M88 gave only rejection codes; these samples were also virtually impossible to count visually.
  • For aligned Ferodo brake lining and friction product samples (20 samples, one talc-process sample excluded), visual count = (0.08 plus or minus 0.02) x (M88 evaluation), with 95% confidence limits. The proportion of variation explained was 0.81.
  • After allowing for the counts on conventionally mounted Ferodo samples, which were on average 34% higher than on matched aligned samples, the equation became visual count = (0.11 plus or minus 0.03) x (M88 evaluation).
  • Mounting method: for textile samples, the conventional method gave counts about 8% lower than the aligned method (geometric mean ratio 0.92), a difference the authors said may be due to random fluctuation. For Ferodo (ratio 1.34) and TAC (ratio 1.20) samples, conventional mounting gave about 30% higher counts.
  • Results for the TAC asbestos cement and insulation product samples were inconclusive. Fibre densities were very low, and the samples came from three factories and from products whose asbestos content and binding materials differ substantially. M88 evaluations for five of these samples were rejected as unreliable, leaving 15.
  • Agreement between laboratories on average M88 evaluations: 95% of textile sample results were within plus or minus 30% of the mean, asbestos cement within plus or minus 40%, and brake lining within plus or minus 15%.
  • Based on experience with the prototype equipment, the participants considered it reasonable to expect one operator using a permanent magnet holding 10 slides to mount, align and assess 50 samples in a normal working day. The trial itself used electromagnets holding four samples.
• The authors' conclusion: The authors concluded that the M88 compared favourably with visual counters for consistency, reliability and speed. They concluded that satisfactory prediction of visual counts depends on calibration, and that textile and brake lining dusts need different calibration factors.
• Limitations the authors state:
  • A calibration should not be assumed to apply to samples from sources other than those used to establish it.
  • The confidence limits reflect only the variability of the visual counts, because the analysis assumes the M88 evaluations have no error.
  • Whether visual counts rise in a straight line with fibre density is open to some doubt.
  • The TAC samples had very low fibre densities, which made visual counting very inaccurate. Samples with higher densities are needed to judge the M88 for these materials.
  • Prototype equipment was used: electromagnets holding four samples replaced the permanent magnets planned for production units.

Related studies

• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)
• A summary of asbestos fibre counting experience in seven countries — G.W. Gibbs, P. Baron, et al. (1977)
• 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)
• The dimensions of airborne asbestos fibres--I. Crocidolite from Kuruman area, Cape Province, South Africa — C.Y. Hwang, G.W. Gibbs (1981)
• A study of the size distributions of airborne amosite fibres in the manufacture of asbestos insulation boards — S.T. Beckett, J.L. Jarvis (1979)
• Real-time measurement of fibers using an HY-differential mobility analyzer with an optical particle counter (KOFAM) — S. Choi, K. Jang, et al. (2017)

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