Comparison of NIOSH and AIA methods for evaluating asbestos fibres: effects of asbestos type, mounting medium, graticule type and counting rules

Our plain-English summary of Comparison of NIOSH and AIA methods for evaluating asbestos fibres: effects of asbestos type, mounting medium, graticule type and counting rules, by E. Gonzalez-Fernandez, F.R. Martín (The Annals of Occupational Hygiene, 1986).

The study

• Authors: E. Gonzalez-Fernandez, F.R. Martín
• Journal: The Annals of Occupational Hygiene
• Published: 1986;30(4):397-410
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The difficulties of evaluating airborne concentrations of asbestos fibres collected on membrane filters are well known. Factors influencing the measurement include the resolving power of the microscope, the type of mounting medium, the type of graticule and the counting rules for fibres. This paper, firstly, compares the results obtained when counting samples (artificially prepared from aqueous suspensions) of chrysotile, amosite and crocidolite according to the NIOSH and AIA guidelines. These specify different mountants, different graticules and different counting rules. The chrysotile samples were taken from the NIOSH PAT Program; the others were prepared by similar methods. The results showed statistically significant differences between methods for chrysotile and crocidolite but not for amosite nor overall. The mean ratio AIA/NIOSH was about 1.2 for chrysotile and 0.5 for crocidolite. Next, chrysotile only samples were evaluated by NIOSH only counting rules, but using different combinations of three mountants and three graticules. When the data were grouped by mounting medium, both acetone vapour and acetone vapour-triacetin gave higher mean values than the NIOSH mountant by almost 2:1. Grouping by graticule gave mean results in descending order Porton: Walton-Beckett: Patterson in the approximate ratios 1.6:1.2:1 by the SNK-test These findings do not necessarily apply to industrial samples which may contain fibres in different states of dispersion mixed with different types and quantities of non-fibrous particulate.

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In plain English

This laboratory study came from a Madrid occupational safety institute and the University of Madrid, Spain. It compared two standard ways of counting asbestos fibres on membrane filters under a microscope: the NIOSH method (P & CAM 239) and the Asbestos International Association (AIA) method (RTM 1). The methods differ in filter-clearing medium, eyepiece grid (graticule) and counting rules. Three counters examined artificially prepared filters. The chrysotile samples came from the NIOSH Proficiency Analytical Testing (PAT) Program, and the crocidolite and amosite samples were made in the laboratory. AIA counts averaged 1.20 times NIOSH counts for chrysotile and 0.53 times for crocidolite, and both differences were statistically significant. For amosite (ratio 0.76) and for all fibre types together, the difference was not statistically significant. In chrysotile samples counted by NIOSH rules, the acetone vapour and acetone vapour-triacetin mountants gave higher mean counts than the NIOSH mountant. The Porton graticule gave the highest counts, then Walton-Beckett, then Patterson. The authors concluded that, for chrysotile, the difference between the methods appeared mainly due to the counting rules. They cautioned that the findings do not necessarily apply to industrial samples.

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: Laboratory comparison of fibre-counting methods (phase-contrast microscopy) on artificially prepared filter samples, analysed by analysis of variance and the Student-Newman-Keuls test
• Who was studied: Membrane filter samples rather than people. There were ten sets of four chrysotile filters each from the NIOSH PAT Program, plus several sets of crocidolite and amosite filters prepared in the authors' laboratory (Madrid, Spain) from UICC standard reference samples. All were counted by three counters (X, Y, Z). Dates are not given.
• Exposure: The NIOSH P & CAM 239 method (mountant D, Porton graticule, NIOSH counting rules) was compared with the AIA RTM 1 method (acetone vapour-triacetin mountant, Walton-Beckett graticule, AIA counting rules) on chrysotile, amosite and crocidolite. Chrysotile was also counted by NIOSH rules using mountants D, acetone vapour and acetone vapour-triacetin, each with Porton, Patterson and Walton-Beckett graticules.
• Main results:
  • The overall mean ratio of AIA to NIOSH counts was 1.20 for chrysotile, 0.53 for crocidolite and 0.76 for amosite.
  • The difference between the methods was statistically significant for the chrysotile and crocidolite samples, but not for amosite or for all samples together.
  • For amosite, results were less consistent and the method difference was not statistically significant.
  • For the PAT chrysotile samples, the authors' NIOSH-method counts averaged 1.15 plus or minus 0.18 times the NIOSH values from all PAT participants.
  • In chrysotile samples counted by NIOSH rules, mean counts were 741 fibres per square millimetre with acetone vapour and 721 with acetone vapour-triacetin, which did not differ significantly from each other. Both were higher than the 376 fibres per square millimetre with the NIOSH mounting medium (significance level less than 0.01).
  • In the same chrysotile samples, the mean count with the Porton graticule (726 fibres per square millimetre) was greater than with the Walton-Beckett graticule (554). Both were greater than with the Patterson graticule (458).
  • For chrysotile, counts with the full NIOSH combination did not differ significantly from counts with the AIA mountant and Walton-Beckett graticule when NIOSH counting rules were used.
• The authors' conclusion: The authors concluded that, for chrysotile samples, the difference between NIOSH and AIA results appeared to be due principally to the difference in counting rules.
• Limitations the authors state:
  • All samples were artificially prepared, so the findings do not necessarily apply to industrial samples. Industrial samples may contain fibres in different states of dispersion mixed with non-fibrous particles.
  • Because the samples were artificially prepared, possible effects of differences in air sampling were not considered.

Topics

Medical terms in this study, explained in our Lexicon: NIOSH, Chrysotile, Amosite, Crocidolite, Triacetin.

Related studies

• Comparison of AIA and NIOSH methods on asbestos fibre measurements in the workplace — E. Gonzalez-Fernandez, P.D. de la Osa, et al. (1987)
• 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 effect of a proposed change to fiber-counting rules in ASTM International Standard D7200-06 — M. Harper, E.G. Lee, et al. (2007)
• A comparison of airborne asbestos fibre counting with and without an eyepiece graticule — S.T. Beckett, R.K. Hey, et al. (1976)
• A comparison of fibre counting across three European national proficiency testing schemes — A.D. Jones, M.C. Arroyo, et al. (2005)
• NIOSH's Respiratory Health Division: 50 years of science and service — K.J. Cummings, D.O. Johns, et al. (2019)

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