Motes and fibers in the air of asbestos processing plants and hygienic criteria for airborne asbestos

Our plain-English summary of Motes and fibers in the air of asbestos processing plants and hygienic criteria for airborne asbestos, by H. E. Ayer, J. R. Lynch (1966).

The study

• Authors: H. E. Ayer, J. R. Lynch
• Published: In: Inhaled Particles and Vapours II, Proceedings of an International Symposium organized by the British Occupational Hygiene Society, Cambridge, 28 Sept.-1 Oct. 1965; Pergamon Press, Oxford, 1966, pp. 511-
• Type of article: Conference paper
• 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 was a descriptive methods paper by two U.S. Public Health Service authors, part of the Service's study of health hazards in the asbestos processing industry. It described the airborne particles found in United States asbestos textile plants. These fell into non-fibrous particles, called motes, and fibers. The paper also weighed methods for sampling and judging airborne asbestos. The authors reported that the impinger dust count, then the basis of the exposure limit, was more than 90% motes. Many airborne asbestos fibers were less than 0.1 micron in diameter, and median fiber lengths were between 1 and 2 microns. Gross mass concentrations of the order of 1-2 mg per cubic meter were observed, and respirable concentrations of 0.2-0.8 mg per cubic meter. The authors estimated that perhaps two-thirds of the respirable mass came from motes and one-third from fibers. They found the impinger method poorly reproducible and limited in sampling time. The authors concluded that motes made up a major portion of exposure and that a battery of methods must be used to characterize the particulate completely. The scanned text is badly damaged and incomplete.

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: Descriptive methods paper (symposium proceedings): a description of airborne particulates in asbestos textile plants and an evaluation of hygienic criteria and sampling methods
• Who was studied: Airborne dust in United States asbestos textile plants, studied as part of the U.S. Public Health Service Division of Occupational Health study of the asbestos processing industry. Fiber counts by operation are given for 1964. No number of plants or samples is stated in the surviving text.
• Exposure: Airborne particulates from asbestos textile processing: asbestos fibers (Canadian chrysotile is named), non-fibrous motes, other process fibers such as cotton and rayon, and air-pollution particles. These were measured by impinger dust count, membrane filter fiber count by phase contrast microscopy, electron microscopy, and mass concentration.
• Main results:
  • In U.S. asbestos textile plants, the impinger dust count was more than 90% motes. It decreased through the years as controls were adopted and improved.
  • For particles that appeared to come from the process, median particle diameters were 0.5 to 1 micron.
  • Many airborne asbestos fibers were less than 0.1 micron in diameter.
  • Median fiber lengths from electron micrographs were between 1 and 2 microns.
  • The authors observed asbestos fibers 75 in length (the unit is lost in the scan) occurring with 1.5 unit density spheres in an aerosol spectrometer sample from an asbestos textile plant.
  • Gross mass concentrations of the order of 1-2 mg per cubic meter, and respirable mass concentrations of 0.2-0.8 mg per cubic meter, were observed in the plants. The authors compared these with average gross outdoor concentrations of 0.1-0.3 mg per cubic meter in typical industrial cities.
  • From microscopic examination of elutriated samples, it appeared that perhaps two-thirds of the respirable mass of airborne dust came from motes and one-third from fibers.
  • The impinger method was described as relatively poor in reproducibility: untrained personnel may differ by a factor of 10 on the same sample. In a recent test cited by the authors, the highest count was typically 2 to 3 times the lowest for the same sample.
  • The X-ray diffraction method (reported by Crable and Keenan) cannot tell asbestos from the accompanying non-fibrous mineral of the same chemical composition, such as chrysotile from serpentine.
• The authors' conclusion: The authors concluded that wherever asbestos is handled, both motes and fibers are generated. By either count or respirable mass, the motes account for a major portion of the particulate exposure. The authors also concluded that a battery of methods must be used to characterize the particulate completely.
• Limitations the authors state:
  • The authors did not have data on fiber concentrations over the years comparable to the impinger dust count data.
  • Particle size counts from electron micrographs were difficult to interpret, because many small particles came from air pollution rather than from asbestos processing.
  • Little quantitative asbestos exposure data was available to match the statistical evidence on lung cancer.

Topics

Medical terms in this study, explained in our Lexicon: Midget Impinger, Fiber Length.

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