Documentation of Threshold Limit Values

Our plain-English summary of Documentation of Threshold Limit Values, by H.B. Ashe, E.J. Baier, A.L. Coleman, et al (1966).

The study

• Authors: H.B. Ashe, E.J. Baier, A.L. Coleman, H.B. Elkins, W.C. Cooper, W.G. Fredrick, B. Grabois, P. Gross, W.J. Hayes JR, K.H. Jacobson, H.N. McFarland, E. Mastromatteo, W.F. Reindollar, R.G. Scovill, R.G. Smith, M.R. Zavon, H.E. Stokinger
• Published: American Conference of Governmental Industrial Hygienists (1966)
• Type of article: Report
• 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 is the 1966 revised (second) edition of a reference work by the Committee on Threshold Limit Values of the American Conference of Governmental Industrial Hygienists. It was a compilation rather than an original study. It drew on published studies, occasional written communications, and committee members' experience to explain the workplace air limits for many substances. The asbestos entry gave a limit of 5 million particles per cubic foot of air (mppcf). The entry said this limit had been recommended by Dreessen and colleagues after a study of 541 employees in three asbestos textile plants using chrysotile. In that study, only three doubtful cases of pneumoconiosis were found among workers exposed below 5 mppcf, and numerous well-marked cases were found above it. The entry also cited animal work in which long fibers, but not short ones, produced fibrosis. The committee stated that conventional dust counts give only an indirect measure of asbestosis risk because of the great relative importance of long fibers. The talc entry (20 mppcf) stated that only tremolitic talc had been definitely associated with diffuse pulmonary fibrosis similar to asbestosis.

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: Compilation and review of published evidence, occasional written communications to committee members, and committee members' experience supporting threshold limit values for many substances (revised edition); not an original study
• Who was studied: No study population of its own. The asbestos limit rests on a cited study by Dreessen et al. of 541 employees in three asbestos textile plants using chrysotile.
• Exposure: Asbestos in general, with chrysotile, amosite, crocidolite and tremolite named. Airborne asbestos dust was measured in million particles per cubic foot (mppcf). Tremolite-containing talc was covered in a separate entry.
• Main results:
  • The threshold limit for asbestos was 5 mppcf, as recommended by Dreessen et al.
  • In the cited Dreessen study of chrysotile textile workers, only three doubtful cases of pneumoconiosis were found in those exposed under 5 mppcf. Numerous well-marked cases were found above 5 mppcf.
  • In cited animal work, long fibers (20 microns and above) produced peribronchiolar fibrosis in lower animals, and short fibers (under 3 microns) gave the reaction of an inert dust.
  • In cited guinea pig experiments, dust with 0.6 per cent fibers longer than 10 microns at 138 mppcf (0.8 million long fibers per cu. ft.) produced experimental asbestosis. Dust with 6.7 per cent such fibers at 40 mppcf (2.7 million long fibers per cu. ft.) produced the reaction in about half the time.
  • The talc entry stated that only tremolitic talc had been definitely associated with diffuse pulmonary fibrosis similar to asbestosis.
  • The talc limit of 20 mppcf was based largely on a cited study of 66 individuals exposed in two mills and mines handling Georgia steatite talc (soapstone) with a 10 percent tremolite content. No pneumoconiosis was found at average dust concentrations of 17 mppcf. Severe and disabling pneumoconiosis was found in groups at 135 and 300 mppcf.
• The authors' conclusion: The committee kept the asbestos limit at 5 mppcf on the basis of the Dreessen study. It stated that conventional dust counts can be expected to give only an indirect measure of asbestosis risk because of the great relative importance of long fibers.
• Limitations the authors state:
  • In the study underlying the asbestos limit, both fibrous and nonfibrous particles were counted, and the nonfibrous particles greatly predominated.
  • The committee stated that the evidence in the compilation is subject to modification as new data appear.

Topics

Medical terms in this study, explained in our Lexicon: Threshold Limit Value (TLV), Million Particles per Cubic Foot (mppcf), Chrysotile, Pneumoconiosis, Fibrosis, Talc, Pulmonary Fibrosis.

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