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 Howard E. Ayer, Jeremiah R. Lynch, Julius H. Fanney (1965).

The study

• Authors: Howard E. Ayer, Jeremiah R. Lynch, Julius H. Fanney
• Published: 1965
• Type of article: Journal article
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This study, by U.S. Public Health Service authors in Cincinnati, compared two methods of measuring airborne asbestos dust in four asbestos textile plants. The older impinger method counted dust particles of all kinds, not only fibers, seen with a lower-power 10x microscope objective, in millions of particles per cubic foot (mppcf). The membrane filter method counted only fibers, in fibers per ml, using a phase contrast microscope. The authors compared 230 pairs of samples taken at the same time. The ratio between the two measurements varied. For total fibers it ranged from 2 to 14 fibers per ml for each mppcf in twisting and from 2 to 20 in weaving. For fibers longer than 10 microns, the ratios of average concentrations ranged from 1.7 to 3.8 across operations. The authors concluded that no single ratio could accurately represent all processes at all times in each plant. They found that individual operations may differ from their overall ratios by a factor of two. Size-selective sampling suggested that most of the fibers counted on the membrane filters were "respirable."

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: Methods comparison study of paired air samples (impinger versus membrane filter) taken at the same time
• Who was studied: 230 paired air samples from five major operations in four asbestos textile plants: 98 pairs from fiber preparation and carding, and 132 pairs from spinning, twisting and weaving. Plant locations and dates are not given.
• Exposure: Airborne asbestos dust in textile plants (fiber type not named). It was sampled by midget impinger in 95 per cent ethyl alcohol and counted with a 10x objective. It was also sampled on Millipore Type AA membrane filters and counted by phase contrast with a 4 mm (43x) objective, counting all fibers, fibers longer than 5 microns, and fibers longer than 10 microns.
• Main results:
  • Total fibers by membrane filter: in twisting, ratios ranged from 2 to 14 fibers per ml for each mppcf by impinger.
  • Total fibers by membrane filter: in weaving, ratios ranged from 2 to 20 fibers per ml for each mppcf for the four plants.
  • For fibers longer than 10 microns, the ratios of average concentrations to impinger counts ranged from 1.7 to 3.8 across operations.
  • In both groups of operations, 90 per cent of impinger counts were below 5 mppcf.
  • In both groups of operations, 90 per cent of membrane filter counts of fibers longer than 10 microns were below 15 per ml.
  • The authors found that no single ratio could accurately represent all processes at all times in each plant.
  • Size-selective sampling with horizontal elutriators suggested that most fibers counted on the membrane filter were respirable.
• The authors' conclusion: The authors concluded that an overall ratio between impinger counts and membrane filter fiber counts could be estimated. They stated that individual operations may have ratios differing from these values by a factor of two, and that most of the fibers counted would reach the lung if inspired.
• Limitations the authors state:
  • Each plant was surveyed only for a brief period, which the authors said probably explains differences in ratios between plants.
  • The comparisons reflect only present conditions. The quality of the fiber was said to have improved since the 1930s, when the impinger-based health studies were done.
  • The two methods used optical systems with different resolutions, so their counts are not directly equivalent.

Topics

Medical terms in this study, explained in our Lexicon: Midget Impinger, Membrane Filter Method, Million Particles per Cubic Foot (mppcf).

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