Even though BLEVEs have been studied by a number of authors, there are still significant gaps in their knowledge and in the prediction of their physical effects. Diverse methodologies have been proposed to calculate the peak overpressure of the explosion, but their results sh ow an important scattering. Most of them assume a reversible, isentropic phenomenon, not at all logical for an explosion. Instead, some recent papers have assumed an irreversible process, much closer to the real phenomenon. This communication analyses these aspects, comparing the results obtaine d by applying the diverse methodologies to data obtained from a real case. The uncertainties found (v essel failure mode, directional effects) are also commented. Finally, some conclusions are derived on the best way to estimate the overpressure.