In December 2005, a succession of events triggered by the lack of redundant level control measures led to the release of large quantities of gasoline from a bulk storage facility in Buncefield near the Heathrow airport in United Kingdom. This article provides an analysis of the reasons behind the extent of the flammable vapor cloud that may have accumulated and the mechanism by which the overpressure was generated. This article also summarizes some of the past incidents involving open-air vapor cloud explosions and the apparent similarities and parallels with the Buncefield incident. The mechanism of the gasoline release and drop from height leads to vapor release and by the time the release hits the ground, most of the vapor is formed. The turbulence of the release itself created turbulence that caused air entrainment. After ignition, the well mixed fuel-air vapor cloud attained higher flame speeds caused by the congestion and turbulence thus further exacerbating the intensity of the explosion. (C) 2011 American Institute of Chemical Engineers Process Saf Prog 30: 138-142, 2011