Under the hazard assessment requirements in 40 CFR Part 68, Subpart B, an owner or operator must analyze worst-case release scenarios and more likely alternative release scenarios, and must document a five-year accident history. If a regulated substance exhibits characteristics of both toxicity and flammability, should owners and operators consider both impacts when performing the hazard assessment?

No. Owners and operators are only required to analyze a regulated substance for the hazard for which it is listed. For example, ammonia is listed as a regulated toxic substance, thus the worst-case release scenario for ammonia must be modeled as a toxic release. However, to make the public and first responders aware of additional hazards, an owner or operator may want to consider the impact associated with an explosion or fire involving a listed toxic substance. Also, as part of the Program 2 hazard review (40 CFR §68.50) and Program 3 process hazard analysis (40 CFR §68.67), all hazards of a regulated substance and the process it is associated with should be considered.