Cal. Gov't Code § 8574.18

(a) For purposes of this article, a “toxic disaster” means an occurrence where toxic substances are dispersed in the environment in such a manner as to cause, or potentially cause, injury or death to a significant number of persons or significant harm to the natural environment, as determined by the implementing state agency, through direct or indirect contact with such toxic substances.
(b) The toxic disaster contingency plan shall provide a listing of the kinds of toxic substances which pose potential hazards to human health and the environment and which could be the subject of a toxic disaster.
For purposes of this article, “toxic substances” means, for highway transportation purposes, substances and materials designated as hazardous by the United States Department of Transportation for purposes of Parts 172, 173, and 177 of Title 49 of the Code of Federal Regulations.