Environmental history of a factory producing friction material

Our plain-English summary of Environmental history of a factory producing friction material, by J.W. Skidmore, B.L. Dufficy (British Journal of Industrial Medicine, 1983).

The study

• Authors: J.W. Skidmore, B.L. Dufficy
• Journal: British Journal of Industrial Medicine
• Published: 1983;40(1):8-12
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004997).

Abstract

The fibre concentrations generated during the production of friction materials, incorporating asbestos, over the past 60 years have been studied to provide cumulative dust exposure data for a mortality study of the work-force. Chrysotile has been used almost exclusively during this period. The measurements made routinely by the factory staff provided information from 1950 onwards; concentrations for earlier years were derived from simulation studies using original materials, machines, and methods. These have shown that while high concentrations prevailed in the earliest years dust suppression measures initiated in 1931, and other factors, reduced the time-weighted average concentrations to moderate levels. There were two four-year periods when the production of brake blocks incorporating crocidolite occupied a well-defined area of the factory. The simulation of this production was not permissible, but the employees concerned could be identified.

In plain English

This study reconstructed the history of airborne asbestos fibre levels over the past 60 years in a factory that had made friction materials, such as brake and clutch linings, since the turn of the century. Its purpose was to supply exposure data for a separate mortality study of the workforce. The factory used African and Canadian chrysotile almost exclusively. Crocidolite was used for two railway brake block orders, received in 1929 and 1939, and each order was produced in one small area over four years. Few early measurements existed, so the authors recreated past working conditions using original machines, materials and methods, helped by long-service employees. Before 1931, grinding and finishing produced up to 50 fibres/ml, and the whole production area was estimated to exceed 20 fibres/ml. In the period after the 1931 Asbestos Regulations, exhaust ventilation generally brought grinding and finishing levels under 10 fibres/ml. Surveys in the 1970s showed almost 100% compliance with the threshold limit value. The crocidolite work could not be simulated or measured, and the authors expected it to have produced appreciably higher levels than chrysotile. The authors concluded that concentrations were high before 1931 and moderate after that.

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: Exposure reconstruction (environmental history) of a single factory, covering fibre concentrations over the past 60 years. It combined routine fibre measurements with simulations of earlier working conditions, using original materials, machines and methods, to provide cumulative exposure data for a separate mortality study.
• Who was studied: One factory in the UK that had produced friction materials (brake and clutch linings, floor coverings) since the turn of the century; the facilities were provided by Ferodo Ltd. Measurements covered four periods: before 1931, 1932-50, 1951-69 and 1970-9. Simulations used long-service employees who volunteered as operatives.
• Exposure: Mainly chrysotile (African and Canadian), as woven cloth from 1910 and as loose fibre from 1922. Crocidolite was used in railway brake blocks for two orders, received in 1929 and 1939, each taking four years in one small area. Small quantities of anthophyllite were also used. Exposure was measured as fibres longer than 5 micrometres per ml, by phase-contrast microscopy.
• Main results:
  • Before 1931, simulated grinding and finishing without exhaust ventilation produced fibre concentrations of up to 50 f/ml.
  • For the first period (before 1931), the authors estimated a concentration above 20 f/ml over the whole production area.
  • In the second period, exhaust ventilation on grinding and finishing machines generally reduced fibre concentrations to under 10 f/ml. Higher levels were seen when the largest components were processed.
  • In the second period, drilling, boring, turning and sawing without exhaust ventilation, and dust dispersed during examination and stencilling, produced up to 8 f/ml.
  • In the 1970-9 period, after extensive dust control improvements, surveys showed almost 100% compliance with the threshold limit value.
  • The airborne fibres were highly respirable. Most had diameters smaller than 1 micrometre.
  • Crocidolite brake block production was not measured. Using chrysotile, the same method produced up to 5 f/ml, and later grinding up to 10 f/ml. The authors expected crocidolite to give appreciably higher concentrations.
• The authors' conclusion: The authors concluded that fibre concentrations were high before 1931 and moderate after that.
• Limitations the authors state:
  • Few airborne fibre measurements existed for the first two periods (before 1950).
  • Measurements from 1968-9 were taken to represent the whole 1951-69 period.
  • Crocidolite work could not be simulated, so crocidolite exposure was not quantified.
  • Not every operation could be reproduced. The simulations were chosen to give general concentration levels for each production stage.
  • Because fibre levels varied with individual working methods and product size, average concentrations could only be given as ranges.
  • Concentrations for office and laboratory staff in the first two periods were estimates, not measurements.
  • Long-term employees said respirators were not regularly used in the second period, so their use should not be assumed.
  • Factory samples from 1968-74 were counted without an eyepiece graticule, which underestimated concentrations by about 15%. The figures from 1968-9 onward were adjusted for this.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Time-Weighted Average (TWA), Crocidolite.

Related studies

• Malignant mesothelioma among employees of a Connecticut factory that manufactured friction materials using chrysotile asbestos — M.M. Finkelstein, C. Meisenkothen (2010)
• Control of the use of asbestos-containing friction materials — M.L. Bentley (1970)
• Occupational and environmental medicine: moving the factory fence or hedging our bets? — P.G. Lewis (2000)
• Mortality among employees of an Ontario factory manufacturing insulation materials from amosite asbestos — M.M. Finkelstein (1989)
• Worker exposure to asbestos during removal of sprayed material and renovation activity in buildings containing sprayed material — N.W. Paik, R.J. Walcott, et al. (1983)
• History and evolution of warning labels for automotive friction products — L.M. Kopelovich, K.A. Thuett, et al. (2014)

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