SEARCH Articles Figures Tables API formula for heat absorbed from fire on wetted surface of pressure vessel. Prepared by permission. Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part I Sizing and Selection, API RP-520, 5th Ed. July 1990, American Petroleum Institute. [Publishers Imprint] See Also: API formula for heat absorbed from fire on wetted surface of pressure vessel. Prepared by permission. Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part I Sizing and Selection, API RP-520, 5th Ed. July 1990, American Petroleum Institute.