During the rapid depressurization of a liquefied gas, its superheating can lead to a boiling liquid expanding vapor explosion (BLEVE). Such an event is of enormous concern during carbon capture and storage (CCS) given the significant amounts of pressurized CO2 involved during its transportation and storage. This article presents, for the first time, the development and validation of a rigorous split-fluid blowdown model for predicting the degree of superheating following the rapid decompression of liquefied gases or two-phase mixtures with particular reference to CO2. The model was successfully validated through a comparison of the predicted vapor-and liquid-phase pressures and temperatures against the recorded data from a number of depressurization tests conducted for pure dense-phase CO2 and its mixtures representing those associated with different capture technologies. The effects of changes in the pressure-relief -valve diameter and CO2 purity on the degree of superheating and, hence, the spontaneity of undergoing a BLEVE were investigated using the model.