When analyzing the worst-case scenario for regulated toxic substances, must I anticipate a specific cause (e.g., fire, explosion, etc.) of the scenario?

No. The worst-case analysis for a release of regulated toxic substances must conform to specific assumptions as identified in § 68.25(c) and (d). Anticipated causes of the release will not affect the analysis, and are not required. A specific cause may be considered in analyzing the alternative release scenarios although it is not a requirement.