For a typical process, two-phase relief device sizing is not normally required for the fire case provided that the relief device is located in the vapor space or on the top of the vessel.
Two-phase relief device sizing should be considered for fire cases if the system has unusually foamy materials or reactive chemicals.
Following Examples References details the two phase fire relief scenarios:
- H. G. Fisher and H. S. Forrest, “Protection of Storage Tanks from Two-Phase Flow Due to Fire Exposure”, Process Safety Progress, Volume 14, No. 3, July 1995, pp 183-199.
- H. Mott, B. Sparrow, “A Simple Relief Valve Rating/Sizing Method for Fire Relief from Liquid-filled Vessels”, presentation to API RP-521 Subcommittee, September 30, 2002.