Re: "TLVs for asbestos"

Our plain-English summary of Re: "TLVs for asbestos", by G.V. Coles (American Journal of Industrial Medicine, 1993).

The study

• Author: G.V. Coles
• Journal: American Journal of Industrial Medicine
• Published: 1993;23(6):955-7
• Type of article: Comment, Letter
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This was a letter to the editor, not a research study. It responded to Warren Cook's 1992 letter "TLVs for Asbestos." The author agreed with Cook, for different reasons, that using the 1946 to 1970 Threshold Limit Value (TLV) to judge employer negligence is erroneous. The 5 million particles per cubic foot asbestos TLV rested on impinger samples counted by light-field techniques. That method could not reliably separate asbestos from other particles. The author agreed that asbestos content in asbestos cement and insulation work was often 15% or less. The author quoted period TLV booklets saying the values were not meant for legislative codes. The author questioned basing an employer's duty of care on the TLV in force at a given date. The author noted that British regulations made in 1932, in force from 1933 for some but not all asbestos processing, set no dust limits. Under the 1937 Factory Act, reducing exposure as far as practicable was obligatory even in other factories. In Britain, no method of measuring levels was suggested as a legal requirement until 1969. The author recommended Britain's 1988 COSHH Regulations as a model.

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: Letter to the editor (opinion and commentary, no new data)
• Who was studied: No study population. The letter responds to Warren Cook's 1992 letter on TLVs for asbestos and discusses exposure standards in the USA (1946 to 1970) and asbestos legislation in Britain.
• Exposure: The ACGIH TLV for asbestos of 5 million particles per cubic foot (mppcf), listed as a silicate and based on impinger samples counted by light-field techniques
• Main results:
  • The author agreed with Cook that it is erroneous to apply a TLV of the period 1946 to 1970 as a basis for determining an employer's negligence in asbestos work during that period, though for different reasons.
  • The author agreed with Cook that no method could reliably distinguish asbestos particles from other particles in impinger counts. The author also agreed that in asbestos cement and insulation settings the asbestos content was frequently as low as 15% or less.
  • The author cited the 1966 ACGIH Documentation as stating that both fibrous and non-fibrous particles were counted in setting the 5 mppcf standard, with non-fibrous particles greatly predominating. The author noted that no method of correcting the count for non-asbestos content was recommended or required.
  • The author quoted the TLV booklet introduction of the time as stating that the TLVs were not considered appropriate for adoption in legislative codes.
  • The author stated that before electron microscope methods were available, a correction would have had to rely on the asbestos content of the source material. The author considered this not appropriate for many dust clouds, because many released fibers are coated in binding matrix material and a large proportion are irrespirable.
  • The author suggested it would not necessarily be proper for hygienists giving expert evidence to use the TLV in force at the date of a measured exposure as the basis of their opinion on an employer's duty of care.
  • The author described British regulations made in 1932 that came into effect in 1933 in some, but not all, categories of asbestos processing undertakings. These regulations contained no specification of airborne dust concentrations.
  • The author stated that under the Factory Act of 1937, reducing asbestos exposure as far as practicable was obligatory, even in factories not specified in the regulations.
  • The author stated that in Britain no specification of a method of measuring levels was then considered appropriate, and none was suggested as a legal requirement until 1969.
  • The author reported involvement in 1957 court proceedings in which an asbestos processing factory was judged not to have limited exposure as far as practicable. The judgment was based on the factory's control actions rather than on air sampling.
• The authors' conclusion: The author recommended close study of the British COSHH Regulations of 1988 as a model. The author argued that applying the COSHH philosophy to PELs, TLVs or other standards would do more to improve workforce health than continued argument about the ethics, motivation and knowledge of those proposing particular values, given resources for inspection and enforcement.

Related studies

• Re: "TLVs for asbestos" — G.W. Schepers (1993)
• ACGIH TLVs: a critical analysis of the documentation — P.A. Breysse (1991)
• Re: "TLVs for asbestos" — T.F. Mancuso (1993)
• Time to reconsider TLVs — L. Djerassi (1988)
• The hygiene standard for chrysotile asbestos — J. Peto (1978)
• Techniques for tracing past employees. An example from an asbestos factory — M.L. Newhouse, J.M. Williams (1967)

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