The Motor Vehicle Safety Standard 208 issued by the U.S. Department of Transportation (1) requires that by August 15, 1975 all cars must have passive restraint systems to protect the occupants in crashes. Of the systems proposed to satisfy the protection requirements, the "air bag" is one of the most promising candidates. Automobile safety cushions are generally inflated using compressed gas cylinders or gas generators. Timely and reproducible inflation of the cushion is certainly a prerequisite to successful operation of the system. However, testing should not be restricted to mechanical performance. Potential toxicity of exhaust products and air dilution with subsequent lack of oxygen have to be included in crash restraint system evaluation. Due to lack of established tolerable thresholds, the post-crash hazard evaluation becomes very difficult. Animal exposure tests with pyrotechnic gas generators for crash restraint applications are described. The rationale used in establishing safe limits for all exhaust products from gas generators is discussed. The problem of air dilution in a closed car is given special attention.