Fiber Length and Aspect Ratio of Some Selected Asbestos Samples

Our plain-English summary of Fiber Length and Aspect Ratio of Some Selected Asbestos Samples, by Ann G. Wylie (1979).

The study

• Author: Ann G. Wylie
• Published: Annals of the New York Academy of Sciences, 330: 605-610 (1979)
• 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 1979 laboratory study measured the shape of particles in four commercial asbestos samples. The samples were short-fiber chrysotile (California), long-fiber chrysotile (Quebec), and amosite and crocidolite (both from Africa). Using a scanning electron microscope, the author measured the length and width of 1200 to 2000 particles per mineral. Aspect ratio (length divided by width) increased with length in all four samples. The average values for each length group closely fit straight lines on logarithmic scales. In chrysotile, width stayed about the same at every length. In crocidolite, and more so in amosite, width rose slightly as length rose. More than 96% of measured particles longer than 5 micrometers had aspect ratios above 10:1, and many exceeded 50:1. The author proposed a value from the model, M, as a possible "fibrosity index" that needs further testing. The author found that most asbestos fibers longer than 5 micrometers had aspect ratios above 20:1. The author suggested that, once asbestos is known to be present, counting only those longer particles with aspect ratios above 20:1 would include most of these fibers. The author also concluded that the 3:1 fiber definition lacks mineralogic justification and should be abandoned.

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: Laboratory mineralogy study measuring particle size and shape by scanning electron microscopy
• Who was studied: Four commercial asbestos samples, with 1200 to 2000 particle measurements per mineral taken from 12 to 20 separate sample preparations: short-fiber chrysotile (New Idria Serpentinite Body, California), long-fiber chrysotile (Jeffrey Mine, Quebec), amosite (Africa) and crocidolite (Africa)
• Exposure: No human exposure was studied. The fiber types characterized were short-fiber and long-fiber chrysotile (not milled), amosite (about 95% grunerite asbestos and 5% actinolite asbestos) and crocidolite. The amosite and crocidolite were both air-jet milled.
• Main results:
  • In all four samples, aspect ratio increased with length. A regression of the mean aspect ratio against the mean length in each length class gave straight-line fits on logarithmic scales (log aspect ratio against log length).
  • The linear models explained the data closely (R2 values): long-fiber chrysotile 97.1%, short-fiber chrysotile 98.2%, crocidolite 99.2%, amosite 98.9%
  • In both chrysotile samples, width stayed constant across length classes. Width increased slightly with length for crocidolite (M = 0.88), and the effect was more pronounced for amosite (M = 0.77).
  • More than 96% of all measured particles longer than 5 micrometers had aspect ratios above 10:1, and many had aspect ratios above 50:1
  • Most asbestos fibers longer than 5 micrometers had aspect ratios above 20:1
  • For long-fiber chrysotile particles longer than 5 micrometers, 99.5% had aspect ratios of 10:1 or more, 96.2% had 20:1 or more, and 76.6% had 50:1 or more
  • For particles shorter than 1 micrometer, the predicted aspect ratios approached those typical of many nonfibrous silicates (less than 5:1)
  • Preliminary results from a study of massive tremolite suggested M values for nonfibrous amphiboles below 0.5
• The authors' conclusion: The author concluded that, once asbestos is known to be present, counting only particles longer than 5 micrometers that have aspect ratios above 20:1 would include most asbestos fibers of that length and probably exclude most nonfibrous mineral fragments. The author also concluded that the 3:1 aspect ratio is not justified on mineralogic grounds and should be abandoned. The author proposed M as a possible "fibrosity index."
• Limitations the authors state:
  • The proposed fibrosity index model needs further testing before it can be considered a reliable measure
  • Aspect ratio alone cannot identify asbestos. A single particle with a high aspect ratio is not necessarily an asbestos fiber.
  • In most cases the width measured was the intermediate dimension of the particle, not its smallest dimension
  • More work is needed to describe the shape and size of the fibrils more accurately

Topics

Medical terms in this study, explained in our Lexicon: Fiber Length, Aspect Ratio (Length-to-diameter ratio), Chrysotile, Amosite, Crocidolite.

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