The effects of sampling practice on the measured concentration of airborne asbestos

Our plain-English summary of The effects of sampling practice on the measured concentration of airborne asbestos, by S.T. Beckett (The Annals of Occupational Hygiene, 1980).

The study

• Author: S.T. Beckett
• Journal: The Annals of Occupational Hygiene
• Published: 1980;23(3):259-72
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The effect of variations in sampling practice upon the measurement of airborne amosite and chrysotile asbestos fibre concentrations by the membrane filter method has been investigated experimentally in a laboratory dust chamber and to a lesser extent in industrial situations. The parameters tested were sampling flow rate and volume, the pore size and electrostatic charge of the filter and the angle of inclination of the sampling head. For all types of filter an increase in the sampled volume resulted in a relative lowering of the measured concentration. This was found to be due to an analytical effect and not to changes in sampling efficiency of the filter. The collection of fibres without a sampling flow accounted for 10% of a sample taken at 200 ml min⁻¹. This effect is therefore only relatively important at very low flow rate. Large (8 µm) pore size membrane filters, when sampling amosite at 2 1. min"', produced a fibre count approximately 15% lower than equivalent measurements on 0.8 µm pore sized filters, although there was no significant fibre penetration completely through this type of filter. Approximately 20% of both amphibole and chrysotile fibres, however, passed through an 8 µm pore size Nuclepore filter at this sampling rate. The electrostatic charge on the filter and the angle of inclination of the sampling head did not appear to significantly affect the measurements.

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

In plain English

This laboratory experiment tested how sampling practice affects membrane filter counts of airborne asbestos fibres. Tests used UICC chrysotile and amosite clouds in a dust chamber, some repeated in two asbestos factories. For equal sampling times, higher flow rates gave lower concentrations in all but one comparison, averaging 1.8-fold between highest and lowest rates. Equal volumes showed no significant flow-rate effect, but a 10-fold larger volume at the same flow rate gave significantly lower results. Filters with no airflow still collected about 10% as many fibres as those sampling at 200 ml per minute. At 2 litres per minute, amosite counts on 8 micrometre cellulose ester filters were 0.85 times those on 0.8 micrometre ones. About 20% of fibres meeting the counting definition passed through 8 micrometre Nuclepore filters at 1 and 2 litres per minute, and about 5% at 100 ml per minute. Filter charge showed no significant effect under the conditions tested, nor did holder angle in still air, which the author cautioned may not hold in high winds. The author concluded that denser fibre loading lowers measured concentration, probably through counting rather than sampling.

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 in a 1 cubic metre still-air dust chamber, with some tests repeated in two asbestos factories
• Who was studied: Not people: air-filter samples taken in clouds of UICC chrysotile and UICC amosite in a dust chamber at the Institute of Occupational Medicine, Edinburgh, plus samples in an asbestos textile factory and an amosite board factory
• Exposure: Sampling parameters for airborne chrysotile and amosite: flow rate (zero, 100 ml/min, 500 ml/min, 2 L/min), sampled volume, filter pore size (0.8 and 8 micrometre cellulose ester and Nuclepore filters), electrostatic charge (Hyamine-treated vs untreated filters), and angle of the filter holder
• Main results:
  • For samples taken for equal times, measured concentration fell as sampling rate rose in all cases but one (500 ml/min vs 2 L/min in chrysotile). The average difference between the highest and lowest flow rates was 1.8 times.
  • Filters with no air drawn through ('zero flow') still collected fibres. Their mean fibre density was about 10% of that on side-by-side samples taken at 200 ml/min, in both chrysotile and amosite clouds.
  • When equal volumes of air were sampled at the three flow rates, no significant difference was found.
  • At the same flow rate (2 L/min), a 5-fold difference in sampled volume gave no significant difference. A 10-fold larger volume gave significantly lower measurements: mean ratio 2.1 for amosite, 1.4 for chrysotile, and 1.8 overall.
  • Pore size for chrysotile at 2 L/min: 0.8 and 8 micrometre cellulose ester filters did not differ significantly (P greater than 0.2; mean ratio 1.05:1 over 12 samples).
  • Pore size for amosite at 2 L/min: 8 micrometre filters gave a mean count 0.85 times that of 0.8 micrometre filters (P less than 0.001). The difference was smaller and not significant at 1 L/min.
  • Penetration right through the cellulose ester filters was too small to measure accurately. Only the 8 micrometre filter showed significant penetration, and only of amosite fibres shorter than 5 micrometres, which are not counted under the hygiene standard.
  • Nuclepore filters: 0.8 micrometre filters showed no measurable penetration. For 8 micrometre filters, about 20% of both chrysotile and amosite fibres fitting the standard counting definition passed through at 1 and 2 L/min. This fell to about 5% at 100 ml/min.
  • In 20 pairs of samples, treated filters in an earthed holder compared with untreated filters in a normal holder gave a mean ratio of 1.04:1, which was not significant (P greater than 0.35).
  • Filters facing at three different angles in relatively still air showed small differences that were not significant (P = 0.78).
• The authors' conclusion: The author concluded that measured concentration depends on the density of fibres on the filter, with more fibres on the filter lowering the measured concentration. The author attributed this probably to effects on the microscope analysis rather than on sampling. Pore size (except for Nuclepore) did not significantly affect results, nor did holder angle when sampling in still air, nor did electrostatic charge under the conditions investigated.
• Limitations the authors state:
  • The orientation results were obtained in relatively still air and may not hold at high wind speeds.
  • Electrostatic effects were tested on a limited number of cloud types, and the author stated that a more detailed study is needed.
  • The effects of exposure time and holder movement on 'zero flow' pick-up could not be measured accurately because samples varied widely.
  • The filter penetration measurements apply only to airborne fibres, not to fibres in liquid.

Topics

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

Related studies

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• Airborne asbestos concentrations in buildings — G.J. Burdett, S.A. Jaffrey (1986)
• Bromo-deoxyuridine (BRDU) uptake in the lungs of rats inhaling amosite asbestos or vitreous fibres at equal airborne fibre concentrations — K. Donaldson, D.M. Brown, et al. (1995)
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• Airborne fiber concentration and size distribution of mineral fibers in area with serpentinite outcrops in Aichi prefecture, Japan — K. Sakai, N. Hisanaga, et al. (2001)
• Mass concentrations of airborne asbestos in the non-occupational environment--a preliminary report of U.K. measurements — G.J. Burdett, J.M. le Guen, et al. (1984)

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