A comparison of impinger and membrane filter techniques for evaluating air samples in asbestos plants

Our plain-English summary of A comparison of impinger and membrane filter techniques for evaluating air samples in asbestos plants, by H.E. Ayer, J.R. Lynch, J.H. Fanney (Annals of the New York Academy of Sciences, 1965).

The study

• Authors: H.E. Ayer, J.R. Lynch, J.H. Fanney
• Journal: Annals of the New York Academy of Sciences
• Published: 1965;132(1):274-87
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

In plain English

This study, by the U.S. Public Health Service, compared two methods of measuring airborne dust in four plants that mainly made asbestos textiles. The authors took 230 pairs of side-by-side samples at fiber preparation, carding, spinning, twisting and weaving. In each pair, one sample was taken with a midget impinger and all visible dust particles were counted (millions of particles per cubic foot, mppcf), a method the authors said may miss very thin asbestos fibers. The other was collected on a membrane filter, and only fibers were counted, using a higher-resolution microscope. The article does not name the asbestos fiber types. Overall, the authors reported that 1 mppcf corresponded to about 10 fibers per ml, or about 3 fibers per ml longer than 10 microns. Ratios differed between plants and operations (for carding, 6 to 27 fibers per ml per mppcf), and most correlations were rather low. The authors stressed that the two counts are not directly comparable. They did not propose the filter method as a substitute and said present results cannot be related directly to past health studies.

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: Comparison of two air sampling and counting methods using paired samples taken at the same time (an industrial hygiene methods study)
• Who was studied: 230 paired air samples (98 from fiber preparation and carding, 132 from spinning, twisting and weaving) taken in four U.S. plants producing primarily asbestos textiles. The dates of sampling are not stated.
• Exposure: Airborne asbestos dust at five textile operations. It was measured by midget impinger (total dust particles counted with a 16 mm, 10x objective) and by membrane filter (fibers counted with a 4 mm, 43x phase contrast objective). The asbestos fiber types are not specified.
• Main results:
  • Across all plants and operations, the ratio of grand means was 9.4 total fibers per ml (membrane filter) for each mppcf (impinger).
  • For carding in four plants, ratios ranged from 6 to 27 fibers per ml for each mppcf.
  • For fiber preparation in four plants, ratios ranged from 4 to 11 fibers per ml for each mppcf.
  • For weaving in four plants, ratios ranged from 2 to 20 fibers per ml for each mppcf.
  • Correlation coefficients for individual plants and operations ranged from small negative values to 0.95, and most were rather low.
  • For fiber preparation and carding, 90 per cent of impinger samples were below 5 mppcf and 90 per cent of membrane filter samples were below 50 fibers per ml.
  • For fibers longer than 10 microns, ratios of average concentrations to mppcf ranged from 1.7 to 3.8 by operation and from 1.2 to 4.5 by plant. The authors put the overall ratio at approximately 1 mppcf to 3 such fibers per ml.
  • In a few membrane filters counted with the same 10x objective used for impinger samples, the fiber counts averaged about the same as the impinger fiber counts, and the particle counts averaged about half the impinger particle counts.
  • In size-selective (elutriator) sampling, the average ratio of unelutriated to elutriated samples was 1.3 for total fibers. The total fiber count was higher in the unelutriated sample in 58 per cent of cases.
• The authors' conclusion: The authors concluded that the overall ratio appeared to be about 1 mppcf by impinger to 10 fibers per ml, or 3 fibers per ml longer than 10 microns, by membrane filter. They added that individual operations may differ from these values by a factor of two. They also concluded that the elutriator results suggested most of the fibers counted on the membrane filter were respirable.
• Limitations the authors state:
  • Very thin asbestos fibers may not be collected by the impinger. If collected, many would not settle in the counting cell in time, and those that did would usually not be visible with the microscope used.
  • The two methods used microscopes of different resolution, so their counts are not equivalent or directly comparable.
  • The comparisons reflect only present conditions. The authors said asbestos fiber quality had changed since the 1930s, so the results cannot be related directly to the past epidemiologic studies.
  • Each plant was surveyed for only a brief period, which probably explains differences in ratios between plants.
  • No single ratio could accurately represent all processes at all times in each plant.
  • The smallest fiber routinely counted by the membrane filter method had not been determined.
  • Too few filters taken alongside impingers were counted for fibers longer than 5 microns to allow direct comparison with impinger samples.
  • Only relatively few elutriator sample sets had been taken, which made firm conclusions difficult.

Topics

Medical terms in this study, explained in our Lexicon: Midget Impinger, Membrane Filter Method.

Related studies

• Inter-laboratory comparisons of the counting of asbestos fibres sampled on membrane filters — S.T. Beckett, M.D. Attfield (1974)
• 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)
• Developments in dust sampling and counting techniques in the asbestos industry — S. Holmes (1965)
• The method used by the U.S. Public Health Service for enumeration of asbestos dust on membrane filters — G.H. Edwards, J.R. Lynch (1968)
• Clearing and mounting techniques for the evaluation of asbestos fibres by the membrane filter method — J.M. Le Guen, S. Galvin (1981)
• Void-counting in assessing membrane filter samples of asbestos fibre — M.D. Attfield, S.T. Beckett (1983)

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