Explosions are rapid combustions that can be divided into two types, according to their propagation velocity:
- DEFLAGRATIONS: When the propagation velocity is subsonic.
- DETONATIONS: When the propagation velocity is supersonic.
Boiling liquid expanding vapour explosion
A special case of explosion is known as BLEVE (Boiling Liquid Expansion Vapor Explosion).
A BLEVE occurs due to the explosion of the highly pressurised vapour generated by the violent boiling of a liquid released suddenly from a vessel, and which would be a gas at ambient pressure, temperature, or pressure and temperature.
The substances that produce a BLEVE are overheated liquids, pressurised liquefied gases, and cryogenic gases. The cause of the explosion is the rupture of the vessel due to overpressure, external impact, or mechanical failure.
If the vapour involved is flammable, it is likely that the resulting cloud of flammable gas released into the atmosphere will ignite immediately after the BLEVE has occurred, forming a fireball. The combustion occurs so rapidly that no pressurised gases are generated, and therefore it is usually considered a gas fire, not an explosion.
Under certain conditions, an unconfined vapour cloud explosion can occur.
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