Measurement of airborne fibers: a review

Our plain-English summary of Measurement of airborne fibers: a review, by P.A. Baron (Industrial Health, 2001).

The study

• Author: P.A. Baron
• Journal: Industrial Health
• Published: 2001;39(2):39-50
• Type of article: Review
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Current fiber measurement techniques arose primarily due to health concerns over asbestos exposure. Fiber toxicity appears to be primarily a function of fiber concentration, dimensions and durability in the lungs. There are two basic approaches to fiber measurement. Fibers can be collected on filters and counted or analyzed by light or electron microscopy; alternatively, fibers can be detected directly using a combination of fiber alignment and light scattering techniques. All of these measurement approaches work best when the fibers are simple rod-shaped particles. However, most fibers can exist as curved rods, complex bundles of fibrils, and agglomerates of fibers and compact particles. These non-ideal shapes contribute to measurement bias and variability.

In plain English

This article, by an author at the US National Institute for Occupational Safety and Health, was a review of methods for measuring fibers in air, including asbestos and man-made fibers such as glass fibers. It did not report new data on workers or patients. The author described two basic approaches: collecting fibers on filters and counting them under a light or electron microscope, or detecting airborne fibers directly with instruments that align the fibers and measure the light they scatter. The review summarized earlier studies showing how method details change results. One cited study found that counts of chrysotile asbestos were 25% lower at a lower microscope magnification, while amosite counts were unaffected. Another found that only about 50% of fibers were counted consistently by all counters. A field comparison found that two direct-reading instruments tended to underestimate fiber concentration compared with phase contrast microscope counting. The author concluded that traditional microscopy methods are relatively inaccurate because of the many sources of error, and that further work is needed to automate fiber counting. The review covered fibers in air only.

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: Narrative review of methods for measuring airborne fibers
• Who was studied: No human or animal population; the review covered techniques for measuring fibers in air
• Exposure: Airborne asbestos (chrysotile and amosite are discussed) and other commercial fibers, including fibrous glass, mineral wool, refractory ceramic fibers, wood and other plant fibers, synthetic organic fibers, and carbon nanotubes
• Main results:
  • The author described two basic measurement approaches: filter collection with counting or analysis by light or electron microscopy, and direct detection using fiber alignment and light scattering
  • Phase contrast light microscopy does not detect all fibers, so the author described it as only an index of exposure
  • A cited study by Pang found that at a lower magnification (400 times), counts were 25% lower for chrysotile asbestos, while amosite counts were unaffected
  • A cited study by Cherrie et al. found that counting depended on how heavily the filter was loaded. Undercounting occurred above 1300 fibers per square millimetre.
  • Most current methods count fibers longer than 5 micrometres with an aspect ratio (length to width) greater than 3 to 1
  • Cowie and Crawford estimated that most counting-rule factors (such as how to count bundles or overlapping fibers) changed the final count by about 20%
  • Inoue found that only about 50% of fibers were consistently counted by all counters, and that an image analysis system did about as well as human counters
  • In transmission electron microscopy, the indirect sample preparation method can break fibers apart, especially chrysotile
  • A cited study found that counting by transmission electron microscopy was less precise than counting the same sample by phase contrast microscopy
  • In a field comparison, two direct-reading instruments (FibreCheck and FM-7400) tended to underestimate fiber concentration compared with phase contrast microscope counting. The FibreCheck detected small-diameter chrysotile fibers especially poorly.
• The authors' conclusion: The author concluded that traditional microscopy methods are relatively inaccurate compared with many chemical analysis methods because of many sources of error in sampling and analysis, and that further work is needed to automate fiber counting
• Limitations the authors state:
  • The review covers only fibers in air. It does not cover measurement of fibers in bulk material or measurement of fiber mass concentration.
  • Most of the discussion assumes straight, simply shaped fibers, although many real fibers are more complex

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Fibril.

Related studies

• Environmental measurements of total dust and fiber concentration in manufacturer and user of man-made mineral fibers — J.H. Kim, H.S. Chang, et al. (1999)
• Measurement of asbestos exposure — J.R. Lynch, H.E. Ayer (1968)
• Airborne concentrations of asbestos in 71 school buildings — M. Corn, K. Crump, et al. (1991)
• Characterization of airborne particles from irreversible hydrocolloids — R.D. Woody, E.F. Huget, et al. (1977)
• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry — T.J. Lentz, C.H. Rice, et al. (1999)

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