Human health and environmental toxicity issues for evaluation of halon replacements

The Clean Air Act Amendments of 1990 require the US Environmental Protection Agency (EPA) to phase out production and use of ozone-depleting chemicals--among them, the fire suppressants, halons. As part of its rulemaking efforts EPA must evaluate the potential hazards to human health and the environment that could result from exposure to compounds that may substitute for halons. The EPA bases health hazard assessment on data obtained in studies involving short-term and long-term exposures. The former are used to evaluate potential risks of acute or delayed effects potentially resulting from short exposures at high concentrations, such as might be experienced in episodic emissions in the workplace. Studies with long-term exposure are used to assess potential adverse effects from continued exposure to low ambient concentrations. In addition, reproductive and developmental hazards are evaluated in several animal species. About ten chlorinated-, brominated-, and/or fluorinated-hydrogen-containing hydrocarbons, to be used alone or in combination, have been proposed as halon substitutes. In addition to health and safety, environmental, efficacy, and marketability considerations (Table I) need to be addressed for the selection of proposed halon substitutes. This presentation will discuss current EPA/Office of Air and Radiation thinking on a decision-tree approach for testing the toxicity of halon substitutes under the Significant New Alternatives Policy program.