Present threshold limit value in the U.S.A. for asbestos dust: a critique

Our plain-English summary of Present threshold limit value in the U.S.A. for asbestos dust: a critique, by E.L. Schall (Annals of the New York Academy of Sciences, 1965).

The study

• Author: E.L. Schall
• Journal: Annals of the New York Academy of Sciences
• Published: 1965;132(1):316-21
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy.

Summary of the article

This paper critically examined the scientific basis of the United States threshold limit value for asbestos dust. That value was 5.0 million particles per cubic foot of air (mppcf) for an eight-hour day, 40-hour week, and was adopted by the American Conference of Governmental Industrial Hygienists and reaffirmed in April 1964. The author traced the value to the 1938 Public Health Service study by Dreessen and colleagues of workers in asbestos textile plants using chrysotile. That study found only three doubtful cases of pneumoconiosis below 5 mppcf. The author identified several limitations of the study. It considered only asbestosis and only American textile plants. Dust counts included all particles, such as cotton and rock dust, and did not separate asbestos fibers. Fibers made up 1 to 8 per cent of particles in most operations and 12 to 26 per cent in weaving. Average counts hid peaks as high as 211 mppcf. The workforce was young and short-term: 333 of 511 employees had worked less than five years, and only 66 more than ten years. The 76 "controls" were themselves exposed to dust. The author concluded that the 5 mppcf value could not be presumed to be a safe limit for asbestos in all applications. The author also noted that the original investigators had offered it only tentatively, "until better data are available."

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This article was a critique, not a new study. The author examined the 1938 U.S. Public Health Service study by Dreessen and colleagues of asbestos textile plants. That study was the basis for the U.S. threshold limit value for asbestos dust: 5.0 million particles per cubic foot of air (mppcf) for a daily eight-hour exposure, 40 hours per week. It examined 541 employees in three plants using chrysotile and found only three doubtful cases of pneumoconiosis among those exposed below 5 mppcf. The author pointed out that the study looked only at asbestosis and only at textile plants. Its dust counts included all particles, such as cotton and rock dust, and few were fibers. The author also noted three other problems. Of 511 employees, 333 had worked less than five years. The "controls" were themselves exposed to dust. Average counts hid peaks of up to 211 mppcf. The original authors had called the figure tentative. The author concluded that the value cannot be presumed to represent a safe limit of asbestos in all applications.

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: Critique (commentary) of the 1938 Dreessen et al. study on which the U.S. threshold limit value for asbestos dust was based; no new data
• Who was studied: No population of its own. The critiqued 1938 study examined 541 employees in three American asbestos textile plants. Elsewhere the article refers to four plants and to 511 employees studied
• Exposure: Asbestos dust (mainly chrysotile) in asbestos textile plants, measured as total particle counts in millions of particles per cubic foot (mppcf). The counts included cotton, rock dust and asbestos fibers. The threshold limit value under review was 5.0 mppcf for a daily eight-hour exposure, 40 hours per week
• Main results:
  • In the 1938 study, only three doubtful cases of pneumoconiosis were found among workers exposed below 5 mppcf, while numerous well-marked cases were found above 5 mppcf
  • The author noted that the 1938 study was limited to textile plants, which tend to use chrysotile only, and considered only asbestosis
  • Dust counts did not separate types of particles, so stone dust, cotton dust and other particles were counted along with asbestos
  • Few fibers were found in the samples: 1 to 8 per cent in crushing, twisting, carding and picking, and 12 per cent in one plant and 26 per cent in another in weaving
  • Of 511 employees studied, 333 had worked less than five years, only 66 more than 10 years, and 73 less than one year
  • The 76 'controls' (49 office workers and other employees, and 27 job applicants) were not true controls, because dust concentrations in their areas ranged from 120,000 to 1,200,000 (units not stated)
  • Average counts hid wide ranges. Pickermen, listed at 34.3 to 74.3 mppcf, could face up to 211 mppcf. Carding, listed at 29.1 mppcf, ranged from 6.4 mppcf at slow speed to 139 mppcf at high speed. Some weaving operations exceeded 140 mppcf
  • The 1938 study was a point survey of people at work, in which sick and dead workers are missed
  • Dreessen and colleagues themselves regarded 5 mppcf as a tentative threshold until better data were available
• The authors' conclusion: The author concluded that because the 5 mppcf value is based on counts of all particles, fibrous or not, asbestos or not, it cannot be presumed to represent a safe limit of asbestos in all applications

Topics

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

Related studies

• The role of threshold limit values in U.S. air pollution policy — J.C. Robinson, D.G. Paxman (1992)
• The origin and development of the asbestos Threshold Limit Value: scientific indifference and corporate influence — D.S. Egilman, A.A. Reinert (1995)
• Developments in dust sampling and counting techniques in the asbestos industry — S. Holmes (1965)
• Economics of dust control — D.W. Hills (1965)
• Corporate influence on threshold limit values — B.I. Castleman, G.E. Ziem (1988)
• Dust measurement and monitoring in the asbestos industry — C.G. Addingley (1965)

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