Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry

Our plain-English summary of Potential significance of airborne fiber dimensions measured in the U.S. refractory ceramic fiber manufacturing industry, by T.J. Lentz, C.H. Rice, J.E. Lockey, et al (American Journal of Industrial Medicine, 1999).

The study

• Authors: T.J. Lentz, C.H. Rice, J.E. Lockey, P.A. Succop, G.K. Lemasters
• Journal: American Journal of Industrial Medicine
• Published: 1999;36(2):286-98
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: To determine dimensions of airborne fibers in the U.S. refractory ceramic fiber (RCF) manufacturing industry, fibers collected through personal air sampling for employees at RCF manufacturing and processing operations have been measured.

Methods: Data were derived from transmission electron microscopy analyses of 118 air samples collected over a 20-year period.

Results: Characteristics of sized fibers include: diameter measurements of <60; 0.19 to 1.0 micron, m of which 75% are less than 0.6 micron and length ranging from < 0.6 to > 20 micron, with 68% of fibers between 2.4 and 20 micron.

Conclusions: Exposures in RCF manufacturing include airborne fibers with dimensions (diameter < 0.1-0.4 micron, length < 10 micron) historically associated with biological effects in pleural tissues. Air sampling data and a review of studies relating fiber size to pleural effects in animals and humans support the belief that information on fiber dimensions is essential for studies with synthetic vitreous fibers.

Copyright 1999 Wiley-Liss, Inc.

In plain English

This article combined an analysis of existing workplace air samples with a review of published studies. The authors pooled 118 personal air samples collected at U.S. plants that make or process refractory ceramic fiber (RCF), a synthetic vitreous fiber. The samples came from three earlier studies (1976, 1988 to 1991, and 1993 to 1995) and had been analyzed by transmission electron microscopy. Fibers thicker than 1.0 micrometer were excluded so the three data sets could be compared. Of the 3,711 fibers sized, 52% were under 0.4 micrometers in diameter and 75% were under 0.6 micrometers. 68% were between 2.4 and 20 micrometers long. The review gathered studies of asbestos and RCF that related fiber size to pleural effects in humans and animals. From it, the authors judged that fibers under 0.1 to 0.4 micrometers thick and under 2 to 10 micrometers long may have greater potency for causing pleural plaques. The authors concluded that RCF manufacturing exposes workers to airborne fibers of sizes historically associated with effects in pleural tissues. They also concluded that future studies should measure fiber sizes. They cautioned that these size estimates came from studies of different fiber types.

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: Analysis of previously collected air sampling data (fiber sizing by transmission electron microscopy) combined with a literature review of studies relating fiber dimensions to pleural effects
• Who was studied: 118 personal air samples from employees at U.S. RCF manufacturing and processing plants, drawn from three studies: 67 samples in 1976 (period A), 28 in 1988 to 1991 (period B), and 23 in 1993 to 1995 (period C)
• Exposure: Airborne refractory ceramic fiber (a synthetic vitreous fiber) in the worker's breathing zone during RCF manufacturing and processing. The literature review also covered asbestos fibers (including chrysotile, tremolite, amosite and amphiboles)
• Main results:
  • 3,711 fibers were sized in total: 2,797 from 67 samples in period A, 565 from 28 samples in period B, and 349 from 23 samples in period C
  • Fibers over 1.0 micrometer in diameter made up 20% (period B) and 33% (period C) of fibers in those sets and were excluded to allow comparison with period A
  • Of all 3,711 fibers (diameter up to 1 micrometer): 52% (1,916/3,711) had diameter less than 0.4 micrometers, 75% (2,769/3,711) less than 0.6, and 89% (3,319/3,711) less than 0.8
  • Of all 3,711 fibers: 19% (709/3,711) were longer than 20 micrometers, and 68% (2,530/3,711) were between 2.4 and 20 micrometers long
  • 45% (1,659/3,711) of all fibers were under 0.4 micrometers in diameter and under 20 micrometers long. By period, the shares were 47% (1,307/2,797) in A, 48% (271/565) in B and 23% (81/349) in C
  • In the reviewed asbestos studies, fiber dimensions associated with pleural changes ranged from 0.03 to 1.5 micrometers in diameter and 0.85 to more than 8 micrometers in length
  • From the literature review, the authors judged that fibers with diameters from under 0.1 to 0.4 micrometers and lengths from under 2 to 10 micrometers may have greater potency for inducing pleural plaque formation
• The authors' conclusion: The authors concluded that exposures to airborne fibers with dimensions historically associated with biological effects in pleural tissues occur in the RCF manufacturing industry. They also concluded that future studies of synthetic vitreous fibers should include data on fiber size distributions.
• Limitations the authors state:
  • Too few data on airborne fiber dimensions were available to identify changes in fiber size over time
  • The critical fiber dimensions were derived from studies of different fiber types, which in some cases were associated with different pleural effects
  • A major assumption is that fibers of the given dimensions found in plaque tissue caused the plaques

Topics

Medical terms in this study, explained in our Lexicon: Fiber Dimensions, Air Sampling, Transmission Electron Microscopy (TEM), Vitreous.

Related studies

• Are airborne refractory ceramic fibers similar to asbestos in their carcinogenicity? — A.M. Walker, L.D. Maxim, et al. (2012)
• Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers — J.E. Lockey, V.L. Roggli, et al. (2012)
• Refractory ceramic fibers: Fiber characteristics, potential health effects and clinical observations — M.J. Utell, L.D. Maxim (2018)
• Exposure to refractory ceramic fibres in the metal industry — M. Linnainmaa, J. Kangas, et al. (2007)
• Refractory ceramic fiber exposure and pleural plaques — J. Lockey, G. Lemasters, et al. (1996)
• Mechanism of refractory ceramic fiber- and rock wool-induced cytotoxicity in alveolar macrophages — K.A. Kim, W.K. Lee, et al. (2001)

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