The rupture of the V-1 vessel appears to have caused a boiling liquid expanding vapor explosion (BLEVE, pronounced ‘blev-ē). A BLEVE is the “sudden loss of containment of a pressure-liquefied gas existing above its normal atmospheric boiling point at the moment of its failure, which results in rapidly expanding vapor and flashing liquid. The release of energy from these processes (expanding vapor and flashing liquid) creates a pressure wave” [1, p. 311]. As required for a BLEVE scenario, the butane/butylene/isobutane mixture in V-1 was above its atmospheric boiling point. Also, the fragmenting of the vessel into multiple pieces, the flattening of Fragment 2 from its original cylindrical shape, and the projecting of the fragments is consistent with a BLEVE scenario.
This BLEVE event, however, differed from the “typical” BLEVE discussed in the literature. The “typical” BLEVE involves flame impinging on the vapor space of a vessel, causing the wall to quickly heat to a high temperature due to the lack of liquid convective heat transfer from the wall. The wall weakens and ruptures, causing the BLEVE. At the PES refinery, however, the fire impinged on the bottom of the V-1 vessel in the liquid space. The CCPS explains that jet fires impinging on the liquid space of a vessel, as is the scenario at PES, can affect the mechanical strength of vessels leading to vessel rupture and a BLEVE. Thus, although this was a somewhat atypical BLEVE event, flame impingement on the bottom of V-1 led to the rupture and BLEVE.
Source: https://www.csb.gov/assets/1/6/pes_final_report_published_october_2022.pdf