Visser, A. and Severnak, S., "Objective Method to Quantify Ecological Toxicity between Friction Materials," SAE Technical Paper 2017-01-2495, 2017.
California and Washington recently passed legislation to limit certain constituents in brake pad friction materials. As part of the California (CA) legislation enacted in 2010, brake pad manufacturers need to perform an alternative assessment to identify potentially safer environmental and toxicological choices for future friction material production. Copper, chromium VI-salts, lead, cadmium, mercury, and other compounds have been identified as potentially unsafe to the environment. This paper contains the methodology behind an objective and comprehensive alternative assessment to quantify the ecological impact of friction materials. Utilizing raw material specific Chemical Abstracts Service (CAS) numbers and their associated toxicological reference values (TRVs), this newly defined method estimates the total toxicological impact of finished friction materials on both the environment and on a human carcinogenic level to allow the manufacturer to screen greener alternatives. Utilizing chemical specific TRVs such as the lethal concentration 50% (LC50), median effective concentration 50% (EC50), and the median effective reproductive concentration 50% (ErC50), this method quantifies ecological impact characteristics of brake pad friction material. In the same regard, the carcinogenic properties of each chemical are evaluated, placed into groupings based on their carcinogenic potential as evaluated by the International Agency for Research on Cancer (IARC) and are utilized to generate comparative carcinogenic ratings. The methodology is best utilized as a relative comparison between multiple uncompressed friction formulations in order to create greener friction material for the future.