Comparison of a fibrous aerosol monitor (FAM) with the membrane filter method for measuring airborne asbestos concentrations

Our plain-English summary of Comparison of a fibrous aerosol monitor (FAM) with the membrane filter method for measuring airborne asbestos concentrations, by P.J. Iles, T. Shenton-Taylor (The Annals of Occupational Hygiene, 1986).

The study

• Authors: P.J. Iles, T. Shenton-Taylor
• Journal: The Annals of Occupational Hygiene
• Published: 1986;30(1):77-87
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

An early production model of the Fibrous Aerosol Monitor (FAM; GCA Corporation) has been compared with the membrane filter method, mainly for chrysotile aerosols, in the laboratory and in asbestos cement, friction material and textile manufacturing factories. Correlation in laboratory trials was fairly good, but it was generally too poor in the workplaces studied for the FAM to be considered as a substitute for the membrane filter method. The FAM could be used for detecting concentration changes of a dust cloud of constant composition, but by this criterion it performed little better than a non-discriminating optical particle counter. The unit tested needed maintenance on three occasions in the 18 months of usage and also its correlation with the membrane filter measurements altered over this time.

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

In plain English

This study compared an early production model of the Fibrous Aerosol Monitor (FAM), a direct-reading instrument designed to count airborne fibres, with the standard membrane filter method, in which fibres are counted under a light microscope. The one instrument was used over 18 months, mainly with chrysotile aerosols, in a laboratory dust box and at four factory sites making asbestos cement, textiles and friction materials. In the laboratory, FAM readings correlated reasonably with filter counts within each set of tests. With chrysotile, however, the ratio between the two fell over the 18 months. In factories, at its main settings, the FAM read between 0.13 and 6 times the filter counts. The FAM also counted non-fibrous particles: about 15% of silicon carbide particles and, apparently, most talc particles. When each was fitted to filter counts with a calibration factor, the FAM's spread resembled that of a non-discriminating Royco particle counter. A second, later FAM registered false counts in clean, filtered air. The authors concluded that the factory correlation was much too poor for the FAM to replace the membrane filter method.

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: Instrument comparison study: a direct-reading fibre monitor was tested against the membrane filter method in laboratory and factory conditions
• Who was studied: One early production FAM, bought by the Health and Safety Executive in Summer 1978 and used over 18 months. It was tested in a laboratory dust box and at four British factory sites making asbestos cement, asbestos textiles and asbestos friction materials. A second, later model received in Spring 1981 was also tried briefly.
• Exposure: Airborne fibre measurement, mainly of chrysotile (UICC chrysotile and a commercial 'factory chrysotile'), plus UICC amosite in the laboratory. The non-fibrous test dusts were silicon carbide and talc.
• Main results:
  • In the laboratory, with both chrysotile and amosite, FAM and membrane filter measurements correlated reasonably within each individual set of experiments.
  • With chrysotile in the laboratory, the ratio of FAM to membrane filter measurements fell over the 18-month test period. The authors had no reason to believe the filter counting had changed.
  • In factory tests with the FAM at ratio 4.0 and amplitude 0.1, FAM readings were between 0.13 and 6 times the membrane filter measurements.
  • In the first asbestos cement factory, with the FAM at ratio 5.0 and amplitude 0.1, the FAM-to-filter factor varied between 4 and 65.
  • The textile factory showed the least variability: FAM readings were 1.8 to 5.3 times the membrane filter measurements.
  • With silicon carbide dust, only 0.3% of particles fitted the usual fibre size definition. Even so, the FAM counted about 15% of particles at the factory settings (ratio 4.0, amplitude 0.1) and about 5% at ratio 5.0, amplitude 0.5.
  • With talc dust, in which fewer than 1% of particles were fibrous, the FAM seemed to count the majority of talc particles passing through it.
  • The FAM's response to the amplitude setting was very similar for chrysotile and talc, so no setting was found that would separate talc from chrysotile.
  • The authors measured the spread of results around a separate best-fit line, forced through the origin, for the FAM and for a Royco particle counter that does not discriminate fibres. In an asbestos textiles factory the spread was 34% for the FAM and 40% for the Royco. In laboratory tests with factory chrysotile it was 19% for the FAM and 25% for the Royco. The authors said that if a factor were used to calibrate the FAM with the membrane filter method, its spread would be similar to the Royco's.
  • The second, later FAM registered spurious counts while sampling filtered clean air at ratio 4.0, amplitude 0.1. At ratio 5.0, amplitude 0.5, it gave no spurious counts but a very low response to chrysotile and silicon carbide test aerosols.
  • During the trials, the first instrument was repaired twice by the manufacturer's agents and was returned to the United States on one of these occasions for recalibration.
• The authors' conclusion: The authors concluded that in factories using chrysotile, where concentrations are mostly below 1 fibre per ml, the FAM's correlation with the membrane filter method was much too poor for it to be a substitute. They suggested it might be used only for an aerosol of fairly consistent composition, and that even then its performance was no better than the non-discriminating Royco particle counter.
• Limitations the authors state:
  • The work was carried out a few years before publication.
  • Only a small amount of work was done with the updated second model.
  • Use of the instrument in laboratory tests with amosite was very limited.
  • The conversion of talc mass measurements into particle numbers was fairly approximate.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Membrane Filter Method, Chrysotile, Asbestos-Cement.

Related studies

• 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)
• 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 comparison of historic asbestos measurements using a thermal precipitator with the membrane filter-phase contrast microscopy method — G. Burdett (1998)
• Inter-laboratory comparisons of the counting of asbestos fibres sampled on membrane filters — S.T. Beckett, M.D. Attfield (1974)
• 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)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.