Asbestos Emissions from Brake Dynamometer Tests

Our plain-English summary of Asbestos Emissions from Brake Dynamometer Tests, by A.E. Anderson, R.L. Gealer, R.C. McCure, et al (1973).

The study

• Authors: A.E. Anderson, R.L. Gealer, R.C. McCure, J.W. Sprys
• Published: Society of Automotive Engineers. Automobile Engineering Meeting, Detroit, MI. May 14-18. (1973)
• Type of article: Conference paper
• 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 1973 conference paper, by researchers on the Ford Motor Co. Scientific Research Staff, reported laboratory tests of how much asbestos fiber a car disc brake releases into the air. A new Pinto disc brake, whose lining the authors estimated contained 42.4% chrysotile asbestos, was run on a brake dynamometer in a room cleaned of other asbestos sources. It was tested under break-in, normal use and high temperature conditions. Air flowing over the brake and background room air were filtered and examined by transmission electron microscopy. The authors found that most of the lining's asbestos was converted to nonfibrous material by the high temperatures at the braking surface. Less than 0.02% of lining wear was released as asbestos fibers, and results were reported as ten times the calculated values to serve as upper bounds. Break-in and high temperature braking increased fiber release. Using data on how car exhaust lead disperses, the authors estimated brake-related asbestos in urban air at below 0.07 nanograms per cubic meter. They judged brakes not a significant source of atmospheric asbestos. They noted that their sample processing obscured fiber sizes.

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: Laboratory brake dynamometer experiment measuring airborne asbestos fiber emissions from a production disc brake, supported by friction visualization tests
• Who was studied: One new production Pinto disc brake assembly tested on a single station brake dynamometer by the Ford Motor Co. Scientific Research Staff (study begun in 1970); no human subjects
• Exposure: Chrysotile asbestos in brake lining, estimated by laboratory analysis at 42.4% of the lining. Brake stops were made from 40 mph: 82 break-in stops, 560 normal use applications and 41 high temperature stops. Airborne fibers were measured by transmission electron microscopy at 40,000X with electron diffraction identification.
• Main results:
  • Most of the lining asbestos was converted to nonfibrous material by the high flash temperatures of the braking surface
  • Less than 0.02% of the lining wear was released as asbestos fibers
  • In the normal use test, asbestos fiber amounted to 0.0023% of the brake lining worn
  • All test results were reported as ten times the calculated values, to allow for possible losses, so that they serve as upper bounds
  • Under normal use, the brake added only 13 ng/m³ (1.3 ng/m³ observed) of asbestos to the undiluted brake exhaust air stream
  • Lining wear during the first 82 break-in stops was about five times the normal use rate; asbestos fiber release during break-in was also higher
  • High temperature use increased lining wear rate by a factor of 11, while asbestos fiber emissions increased by less than a factor of three
  • The largest asbestos fiber on the normal use test filter (0.13 μm in diameter and over 1.2 μm long) was about the same size as that on the background filter, and larger fibers appeared no more numerous on the test filter than on the background filter
  • Lining surfaces contained nonfibrous magnesium silicate (a thermal degradation product of chrysotile) in crystalline (forsterite) and amorphous forms, and brake flash temperatures up to 980°C were confirmed
  • Using automotive exhaust lead dilution data, the asbestos fiber concentration in urban air due to brake usage was conservatively estimated at less than 0.07 ng/m³
• The authors' conclusion: The authors concluded that, based on this upper bound, brake use was not a significant source of atmospheric asbestos, and that intense local heating and mechanical action decompose most asbestos fiber in brake linings during typical use
• Limitations the authors state:
  • The clarification process used to count fibers obscured the actual fiber size distribution
  • The similar, low fiber content of background and test filters prevented an estimate of fiber size distribution
  • In the break-in and high temperature tests the filter was in one central location, and thus possibly not representative
  • Pad drag caused extra outboard lining wear in the normal use test, which was not included in the wear rate calculations; the authors expected no adverse effect on results

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Transmission Electron Microscopy (TEM), Fiber Release.

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