The Effect of Aspect Ratio On Fiber Counts A Preliminary Study

Our plain-English summary of The Effect of Aspect Ratio On Fiber Counts A Preliminary Study, by A.A. Winer, M. Cossette (1979).

The study

• Authors: A.A. Winer, M. Cossette
• Published: Annals of the New York Academy of Sciences (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 preliminary round robin study tested whether raising the aspect-ratio criterion (length to width) in the NIOSH optical fiber-counting method improves counting precision. Government, research and industry laboratories counted membrane filter samples, two from each of six plants (asbestos-cement, brake linings, mining mill, textiles). They sorted fibers by length and by aspect ratio (3:1 to 5:1, 5:1 to 10:1, over 10:1). Counters found aspect ratio much harder to judge than length, and said many particles in the 3:1 and 5:1 groups did not look like chrysotile. The Conclusion reported that using 10:1 instead of 3:1 cut relative error from 93 to 42%, while about 45% fewer fibers were counted. However, the Summary table gave a higher coefficient of variation for 10:1 (0.54) than for 3:1, and judged 5:1 better than 3:1. In a parallel electron microscopy (TEM) study, about 1 in 50 fibers longer than 5 um present was counted optically, and most such fibers had aspect ratios above 10:1. The authors concluded that raising the aspect ratio above 5:1 should improve precision, to be verified in a second round robin.

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: Preliminary inter-laboratory round robin comparison of optical (phase contrast) fiber counting, with a parallel transmission electron microscopy (TEM) count at one laboratory
• Who was studied: Membrane filter air samples, two from each of six plants (asbestos-cement, brake linings, mining mill and textile industries), counted by government, research and industrial laboratories in Canada and the United States. The text gives 11 laboratories in one place and twelve in another. One group of similar samples was also examined by TEM at the Ontario Research Foundation. Sampling dates are not given.
• Exposure: Not a health study. Fibers on the filters were classified by length (5 to 10 um, 10 to 50 um, over 50 um) and by aspect ratio (3:1, 5:1 and 10:1 criteria). The TEM sizing tables are labelled as chrysotile.
• Main results:
  • In the optical counts (fibers per square mm), the mean shares of the total count were 16.7% in the 3:1 to 5:1 group, 26.6% in the 5:1 to 10:1 group and 56.67% (as printed) in the over 10:1 group
  • Variability between counts was much greater for the aspect ratio groups than for the length groups
  • Fibers 5 to 10 um long made up an overall mean of 62% of the optical count, with a standard deviation of 11%
  • Fibers longer than 50 um (as printed, those less than 2 um in diameter) all had aspect ratios greater than 10:1
  • Counters reported that aspect ratio was much more difficult to determine than length
  • Counters reported that many particles in the 3:1 and 5:1 aspect ratio groups were not chrysotile, judging by their prismatic appearance, yet all were counted as asbestos
  • In the Conclusion section, using a 10:1 instead of a 3:1 aspect ratio reduced relative error from 93 to 42%, while the number of fibers counted fell by approximately 45% (printed as '457')
  • The Summary section's table gave mean counts and coefficients of variation (5 um minimum length) of 100 and 0.43 (printed '043') for 3:1, 80 and 0.38 for 5:1, and 53 and 0.54 for 10:1. For 3:1 with a 10 um minimum length the figures were 38 and 0.49 (printed '049'). On this basis the Summary judged 5:1 better than 3:1, and a 5 um minimum length better than 10 um.
  • For fibers longer than 5 um, TEM and optical counts were related: about 1 fiber was counted optically for every 50 present
  • For fibers shorter than 5 um, no such relationship was found; the average count ratio was 1:1000
  • By TEM, most fibers longer than 5 um had aspect ratios greater than 10:1, ranging from about 60% to over 80% of fibers counted per sample
  • In TEM sample CCM16-02, about 55% of fibers had aspect ratios greater than 10:1, 41% (printed '417') between 5:1 and 10:1, and 4% under 5:1. In sample 2K326, about 76% were greater than 10:1, about 24% between 5:1 and 10:1, and less than 1% under 5:1.
• The authors' conclusion: The authors concluded that the preliminary round robin indicated better optical counting precision with a 10:1 aspect ratio than with 3:1. They stated that increasing the aspect ratio to greater than 5:1 should increase precision, which can be verified in the next round robin.
• Limitations the authors state:
  • This was a preliminary series. A second, statistically designed round robin was being planned to avoid the problems encountered.
  • Some slides were too dense and some too light, which made counting difficult
  • Assigning aspect ratios to fibers 5 to 10 um long was difficult when the fiber diameter was small
  • Failure to adjust graticule marks to the exact length required can cause a bias that depends on counter and microscope
  • The optical microscope does not allow all fibers to be counted, particularly very short and thin ones

Topics

Medical terms in this study, explained in our Lexicon: Aspect Ratio (Length-to-diameter ratio), NIOSH, Asbestos-Cement, Brake Lining, Chrysotile.

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