For the purpose of analyzing the worst-case release scenario required as part of the hazard assessment at 40 CFR Part 68, Subpart B, the worst-case release quantity is identified as the greatest amount held in a single vessel or pipe, taking into account administrative controls that limit the maximum quantity (40 CFR §68.25(b)). Why did EPA choose to allow consideration of administrative controls when determining the worst-case release quantity?

EPA's decision to allow administrative controls to be considered when determining the worst-case release quantity was based on the historical reliability of such controls and the role that such a provision could play in encouraging their further use. This approach acknowledges the efforts by sources to increase process safety by intentionally reducing the inventory of regulated substances (e.g., vessels kept at half capacity to allow for process upsets, emergency shutdowns, and deinventorying or maintenance turnarounds) (61 FR 31682; June 20, 1996). Since the worst case scenario assessment implies that this kind of an event could occur at any time, the scenario must account for the maximum amount contained at any one time, including amounts potentially added to the vessel inventory during an emergency or shutdown.