Definition(s)
Volumetric Heating
On the other hand, reactive systems in which an external fire can result in an exothermic reaction are subject to boiling throughout the volume of the vessel due to heat evolved from the reaction. This is commonly referred to as volumetric heating, which results in more liquid-swell than wall-heating and, thus, increases the potential for longer-duration two-phase relief.
Source: API STD 521, Pressure-relieving and Depressuring Systems, Fifth Edition, January 2007 (Addendum May 2008). Global Standards