Air-Borne Asbestos

Our plain-English summary of Air-Borne Asbestos, by H.E. Ayer, J.R. Lynch.

The study

• Authors: H.E. Ayer, J.R. Lynch
• Published: n.d.
• 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 paper was written in connection with a U.S. Public Health Service study of the asbestos processing industry. It described the airborne dust in asbestos textile plants and compared ways of measuring it. The authors separated airborne particles into non-fibrous particles, which they called 'motes', and asbestos fibers. Many fibers were short: median lengths measured from electron micrographs were between 1 and 2 microns. Microscope examination suggested that perhaps 2/3 of the respirable dust mass (a fraction of the dust defined by particle size) came from motes and 1/3 from asbestos fibers. The existing U.S. limit of 5 mppcf (million particles per cubic foot) relied on the impinger counting method. In asbestos textile plants where the only dust generated comes from the asbestos, the particles that method counted were more than 90 percent motes. Its agreement with fiber counts taken at the same time ranged from poor to fair. The authors cited a recent test in which one sample was read by observers in different organizations; the highest count was typically 2 to 3 times the lowest. The authors argued that counting fibers gives a reasonably direct index of asbestosis hazard.

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 and methods paper: it described airborne particulates in asbestos textile plants and compared sampling methods against criteria for measuring exposure
• Who was studied: Air samples taken in U.S. asbestos textile plants. The number of plants and the dates cannot be read in the supplied text.
• Exposure: Airborne dust in asbestos textile processing, considered as two types: non-fibrous particles ('motes') and asbestos fibers. Canadian chrysotile is mentioned, and chrysotile, amosite and crocidolite are discussed for x-ray diffraction analysis.
• Main results:
  • Air samples showed mostly separate particles with few clumps
  • Many airborne fibers were short. Median lengths from electron micrographs were between 1 and 2 microns. The unit symbol is garbled in the OCR, but the article measures particle sizes in microns throughout.
  • From microscope examination of samples, perhaps 2/3 of the respirable mass of airborne dust came from motes and 1/3 from asbestos fibers
  • The proportion of motes appeared to be greater in fiber preparation than in later operations
  • The existing U.S. threshold limit value was 5 mppcf of total dust as measured by the impinger method
  • In asbestos textile plants where the only dust generated comes from the asbestos, the particulate counted by the impinger method was more than 90 percent motes
  • In simultaneous samples, the correlation between impinger counts and fiber counts ranged from poor to fair
  • For non-textile operations involving other dusts, the authors stated that the impinger count would not give a reliable index of fiber concentration
  • In a recent test cited by the authors (not one they report conducting), the same sample was given to observers in different organizations; the highest count was typically 2 to 3 times the lowest
  • Most of the respirable dust would be motes, so respirable mass, like the impinger count, would be only an indirect index of fiber concentration
  • Where large enough air samples can be obtained, the authors considered x-ray diffraction appropriate for mixed dusts from other asbestos product operations
• The authors' conclusion: The authors stated that, since fibers cause asbestosis, a count of fibers from an air sample provides a reasonably direct index of the asbestosis hazard
• Limitations the authors state:
  • Too few mass-concentration results were available to present averages
  • The limited data on respirable mass were insufficient to show whether the fiber proportion really differed between operations
  • Particle size distributions from electron micrographs were difficult to interpret because many small particles came from air pollution rather than the asbestos process

Topics

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

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