Do the quantities of interconnected vessels need to be aggregated for the worst-case release scenario analysis?

Pursuant to the risk management program regulations, facilities must perform an offsite consequence analysis for the worst-case release scenario. Do the quantities of two separate vessels that are interconnected with a closed valve need to be aggregated for the worst-case release scenario analysis?

No. Worst-case release is defined as the release of the largest quantity of a regulated substance from a vessel or process line failure that results in the greatest distance to an endpoint (40 CFR §68.3). Therefore, the worst-case release scenario should only include the largest quantity of a regulated substance from a single vessel or pipe, taking into account administrative controls that limit the maximum quantity, not what could potentially be drained from equipment interconnected with a failed vessel or pipe. The worst case scenario could also involve the amount in a smaller vessel that is held at a higher temperature or pressure, or that is located closer to the boundary of the stationary source, if those conditions would result in a greater distance to an endpoint beyond the stationary source boundary than the scenario involving the largest vessel or pipe (40 CFR §68.25).