Sizing emergency venting for atmospheric flammable liquid storage tanks is a safety-critical requirement, yet we often find it undersized. The core objective is to provide sufficient relief capacity so that, in the event of an external “exposure fire,” the tank does not rupture due to rapid internal pressure buildup from vaporizing liquid. Unlike normal venting (which handles thermal expansion or breathing during filling/emptying), emergency venting is sized for fire exposure. We must ensure that the combined capacity of our normal vents and our emergency vents prevents the tank pressure from exceeding the tank’s Maximum Allowable Working Pressure (MAWP). The industry standard for this calculation is NFPA 30: Flammable and Combustible Liquids Code.