The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method

Our plain-English summary of The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method, by A.M. Johnston, A.D. Jones, J.H. Vincent (The Annals of Occupational Hygiene, 1982).

The study

• Authors: A.M. Johnston, A.D. Jones, J.H. Vincent
• Journal: The Annals of Occupational Hygiene
• Published: 1982;25(3):309-16
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This paper describes experiments carried out in the laboratory to clarify interpretation of the role of sampling flow rate and wind speed on the efficiency of sampling airborne asbestos fibres in workplaces. The experiments were carried out with test clouds of UICC amosite and UICC chrysotile with aerodynamic characteristics sufficiently close to those of workplace dusts to allow direct comparison to be made, at least as far as the immediate aims of this enquiry are concerned. It was shown unambiguously, for conditions of practical interest, that there were no significant effects of sampling flow rate and wind speed on the measurement of fibre mass concentration and fibre number concentration respectively. Thus, any observed bias in the measurement of fibre concentration by manual counting must instead be attributable to psychological effects relating to the density of fibres on the filter. On the basis of these results, it is suggested that recommended procedures which impose limitations on sampling flow rate or face velocity are unnecessarily restrictive. Rather it is preferable to tighten up the prescribed limits on fibre density on the filter.

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

In plain English

This was a laboratory experiment, not a study of workers or of health. The authors tested whether the sampling flow rate or the surrounding wind speed changes how much airborne asbestos the membrane filter method measures. They generated clouds of UICC amosite and UICC chrysotile in a 1 cubic metre chamber. In still air, measurements of collected dust mass showed no dependence of sampling efficiency on flow rate for either fibre type. In almost 50 sets of equal-volume amosite samples, fibre counts showed no obvious bias toward the lower or the higher flow rate. In a small wind tunnel at wind speeds of 0, 1 and 4 metres per second, amosite results showed some suggestion of a slight deviation, particularly at high wind speed. The authors judged that there was no significant dependence for practical purposes. The authors concluded that rules limiting sampling flow rate or face velocity were unnecessarily restrictive, and that limits on fibre density on the filter should be tightened instead. They stressed that this applies only to asbestos or other aerodynamically fine dusts.

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 experiment on air-sampling methods (no human subjects)
• Who was studied: Laboratory-generated dust clouds of UICC amosite and UICC chrysotile in a 1 cubic metre Perspex calm-air chamber; no people were studied
• Exposure: UICC amosite and UICC chrysotile test clouds, sampled at a range of sampling flow rates. The moving-air tests used nominal flow rates of 1, 4 and 8 litres per minute at wind speeds of 0, 1 and 4 metres per second (amosite only).
• Main results:
  • In calm air, the dust mass collected on filters showed no dependence of sampling efficiency on sampling flow rate, for both UICC amosite and UICC chrysotile
  • In the calm-air mass experiments, the run-to-run variation in the mass ratio was generally within 10% of the mean
  • Almost 50 sets of three equal-volume samples were taken at paired flow rates for fibre counting (UICC amosite only)
  • Counts of UICC amosite fibres on equal-volume samples showed no obvious bias between the lower and the higher flow rate. The authors concluded that, for practical purposes, there was no aerodynamic effect.
  • In moving air (UICC amosite), there was some suggestion of a slight deviation from ideal behaviour, particularly at high wind speed
  • Despite that deviation, the authors concluded that, for practical purposes, sampling efficiency did not depend significantly on external aerodynamic factors
• The authors' conclusion: The authors suggested that recommended procedures limiting sampling flow rate or face velocity are unnecessarily restrictive, and that it is preferable to tighten the prescribed limits on fibre density on the filter
• Limitations the authors state:
  • The authors stated that their conclusions and recommendations apply only to asbestos fibres or other aerodynamically fine dusts, not to coarser dusts
  • The authors stated that it needs further investigation whether their suggested range of fibre density on the filter is acceptable, given a possible psychological bias in counting

Topics

Medical terms in this study, explained in our Lexicon: Membrane Filter Method, UICC, Amosite, Chrysotile.

Related studies

• Comparison of a fibrous aerosol monitor (FAM) with the membrane filter method for measuring airborne asbestos concentrations — P.J. Iles, T. Shenton-Taylor (1986)
• A comparison of fibre counting stopping rules in the application of the membrane filter method — N.P. Crawford, W.M. Maclaren, et al. (1987)
• Comparison of direct and indirect methods of measuring airborne chrysotile fibre concentration — C. Eypert-Blaison, S. Veissiere, et al. (2010)
• A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy — J.R. Hoyes, R. Clayton (1980)
• Conversion of the asbestos fibre concentration recorded by means of the konimeter and the thermal precipitator to that expected by means of the membrane filter method — R.S. du Toit, T.C. Gilfillan (1979)
• A comparison of historic asbestos measurements using a thermal precipitator with the membrane filter-phase contrast microscopy method — G. Burdett (1998)

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