Boiling liquid expanding vapor explosion. A specific type of fireball that can occur as the result of the situation where a vessel containing a pressurized liquid comes in direct contact with external flame. As the liquid inside the vessel absorbs the heat of the external fire, the liquid begins to boil, increasing the pressure inside the vessel to the set pressure of the relief valve(s). The heat of the external fire will also be directed to portions of the vessel where the interior wall is not “wet” with the process liquid. Since the process liquid is not present to carry heat away from the vessel wall, the temperature in this region (usually near the interface of the boiling liquid), will rise dramatically causing the vessel wall to overheat and become weak. A short time after the vessel wall begins to overheat, the vessel can lose its structural integrity and a rupture will occur. After vessel rupture, a fireball will usually result with the external fire available as the ignition source.

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