BLEVE, pronounced blevy, is an acronym for Boiling Liquid Expanding Vapour Explosion. This is a type of explosion that can occur when a vessel containing a pressurized liquid is ruptured. Such explosions can be extremely hazardous. When the liquid is water, the explosion is usually called a steam explosion.
A BLEVE can occur in a vessel that stores a substance that is usually a gas at atmospheric pressure but is a liquid when pressurized (for example, liquefied petroleum gas). The substance will be stored partly in liquid form, with a gaseous vapour above the liquid filling the remainder of the container.
If the vessel is ruptured - for example, due to corrosion, or failure under pressure - the vapour portion may rapidly leak, dropping the pressure inside the container and releasing a wave of overpressure from the point of rupture. This sudden drop in pressure inside the container causes violent boiling of the liquid, which rapidly liberates large amounts of vapour in the process. The pressure of this vapour can be extremely high, causing a second, much more significant wave of overpressure (i.e., an explosion) which may completely destroy the storage vessel and project it as shrapnel over the surrounding area.
A BLEVE does not require a flammable substance to occur, and therefore is not usually considered a type of chemical explosion. However, if the substance involved is flammable, it is likely that the resulting cloud of the substance will ignite after the BLEVE proper has occurred, forming a fireball and possibly a fuel-air explosion. BLEVEs can also be caused by an external fire nearby the storage vessel causing heating of the contents and pressure build-up.
Significant industrial BLEVEs include the accidents at Feyzin in France in 1966, Texas City, Texas in 1978, and San Juan Ixhuatepec in Mexico in 1984.