Measurement of Airborne Asbestos Dust

Our plain-English summary of Measurement of Airborne Asbestos Dust, by S.A. Roach (1965).

The study

• Author: S.A. Roach
• Published: Annals of the New York Academy of Sciences (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 paper described a field comparison of dust-measuring instruments in the disintegrator department of an asbestos factory where crude amosite fiber was processed. Under the microscope the airborne dust was mostly short, thin, straight fibers, and ninety-four per cent of particles were less than 0.5 microns wide. Eight instruments were run side by side until 10 trouble-free days of sampling had been collected. Particle and fiber counts varied with the instrument and microscope used. For all visible particles, the midget impinger averaged 1.1 million particles per cubic foot. The thermal precipitator gave 2.8 to 10.8, depending on magnification, and the Royco automatic counter gave 20.9. The mass samplers agreed more closely: 1.06 and 0.94 milligrams per cubic metre for dust of all sizes, and 0.34 and 0.29 for respirable dust. The author concluded that measuring mass was simpler than counting particles, and that the UNICO respirable dust sampler was the best available type for these workers. The author noted that none of the instruments was very suitable for measuring dust inhaled by someone wearing a face mask.

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: Field comparison of airborne dust sampling instruments in one asbestos factory department. Eight instruments were sampled side by side for six hours a day until 10 trouble-free days were accumulated. No health outcomes were studied.
• Who was studied: Airborne dust in the disintegrator department of one asbestos factory where crude amosite fiber was processed, and the dust exposure of its workers, including a bagging machine operator. The text gives no year or count of workers.
• Exposure: Airborne amosite dust from mechanically opening and bagging crude amosite fiber. The author reported that no cotton, wool or other organic fiber was used in the plant.
• Main results:
  • In thermal precipitator samples, 94 per cent of particles were less than 0.5 microns wide and 0.6 per cent were thicker than one micron.
  • Alongside the nearest house, about 250 feet from the plant, the dust concentration was too small to measure with the midget impinger (less than 0.01 million particles per cubic foot).
  • Air behind the face mask filter pads, judged to represent the dust actually inhaled, measured below 0.1 million particles per cubic foot by the impinger method.
  • For all visible particles, the mean of 20 midget impinger samples was 1.1 million particles per cubic foot.
  • For all visible particles, the thermal precipitator gave means of 2.8, 5.5 and 10.8 million particles per cubic foot under increasingly powerful microscope objectives.
  • For all visible particles, the mean of 240 Royco automatic counter readings was 20.9 million particles per cubic foot.
  • Fibers (longer than five microns, length more than three times width) averaged 0.11 million fibers per cubic foot in midget impinger samples.
  • Fiber counts were higher with the thermal precipitator, starting at 0.31 million fibers per cubic foot under the lowest-power objective.
  • For dust of all sizes, the mean of 10 electrostatic precipitator samples was 1.06 milligrams per cubic metre and the mean of 10 soxhlet samples was 0.94.
  • For respirable dust, the UNICO respirable dust sampler gave a mean of 0.34 milligrams per cubic metre and the hexhlet 0.29.
  • About one-third of the weight of the dust was in particles of respirable size.
  • In this particular dust cloud, the 5 million particles per cubic foot hygienic standard appeared to correspond to about 1.5 milligrams per cubic metre of respirable dust.
  • The author judged the UNICO instrument to be the best available type for measuring these workers' dust exposure.
• The authors' conclusion: The author concluded that measuring mass concentration was far simpler than measuring number concentration. The author also concluded that there appeared to be no better method for continually monitoring many workers than measuring the mass concentration of respirable dust.
• Limitations the authors state:
  • The exact boundaries defining respirable dust are uncertain and vary from person to person and with breathing pattern.
  • The Royco counter's calibration for fibrous dust is uncertain.
  • None of the instruments tried was very suitable for measuring the dust actually inhaled by a mask wearer.
  • The midget impinger does not collect many particles shorter than one micron.
  • Some workers had poorly fitting masks or did not wear them, so general-area samples would need supplementing with time studies and mask-fit tests.

Topics

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

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