HUMAN HEALTH AND ENVIRONMENTAL TOXICITY ISSUES FOR EVALUATION OF HALON REPLACEMENTS

The Clean Air Act Amendments of 1990 require the US Environmental Prot ection 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 h ealth and the environment that could result from exposure to compounds that may substitute for halons. The EPA bases health hazard assessmen t on data obtained in studies involving short-term and long-term expos ures. The former are used to evaluate potential risks of acute or dela yed effects potentially resulting from short exposures at high concent rations, such as might be experienced in episodic emissions in the wor kplace. Studies with long-term exposure are used to assess potential a dverse effects from continued exposure to low ambient concentrations. In addition, reproductive and developmental hazards are evaluated in s everal animal species. About ten chlorinated-, brominated-, and/or flu orinated-hydrogen-containing hydrocarbons, to be used alone or in comb ination, have been proposed as halon substitutes. In addition to healt h and safety, environmental, efficacy, and marketability consideration s (Table I) need to be addressed for the selection of proposed halon s ubstitutes. This presentation will discuss current EPA/Office of Air a nd Radiation thinking on a decision-tree approach for testing the toxi city of halon substitutes under the Significant New Alternatives Polic y program.