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Project Status: complete

Title: Determination of asbestos content of current automotive dry friction materials, and the potential contribution of asbestos to particulate matter derived from brake wear.

Principal Investigator / Author(s): Stephen Wall

Contractor: California Department of Health Services

Contract Number: 01-333

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels, Monitoring


Motor vehicle brake dust emission rates and brake friction material inventories of asbestos, a known carcinogen, are currently largely unknown. Assessment of the potential health effect consequences from asbestos brake friction materials (BFM) requires the identification of the asbestos fiber type and classification of fiber size, as well as, the determination of the asbestos concentration in brake dust emissions. Field collection of used brake shoes from likely target vehicles indicates that very high levels of chrysotile asbestos (20-60% by mass) are still present in brake friction material (BFM) for some models, primarily in rear drum brakes. Similar to deposited dust collected from the braking system surfaces of these target vehicles, air emissions for a test vehicle operating over standard dynamometer emission cycles contained chrysotile fibers < 10 um length. Due to apparent frictional heating effects, less than 1% of the asbestos mass originally present in the BFM can be identified in both the deposited brake dust, and the airborne brake dust emission during test vehicle chassis dynamometer driving cycles. However, health effects concerns associated with the measurable level of small asbestos fibers in the air emissions may warrant early brake replacement, before warranted by wear, with the now widely available non-asbestos BFM, for a group of target vehicles, with brake shoes installed before calendar year 2000.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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