Boiling liquid expanding vapor explosion

If the vessel's integrity is compromised, the loss of pressure drops the boiling point, which can cause the liquid to convert to gas expanding rapidly.

On 24 April 1957, a process reactor at a Factory Mutual (FM) facility underwent a powerful explosion as a consequence of a rapid depressurization.

In the wake of the accident, researchers James B. Smith, William S. Marsh, and Wilbur L. Walls, who were employed with FM, came up with the terms "boiling liquid expanding vapor explosion" and its acronym "BLEVE".

Typically, a BLEVE starts with a vessel containing liquid held above its atmospheric-pressure boiling temperature.

If the rupture is catastrophic, i.e., the vessel becomes suddenly no longer capable of holding any pressure, then the liquid will find itself at a temperature far above its boiling point.

Depending on temperatures, pressures and the material involved, the expansion may be so rapid that it can be classified as an explosion, fully capable of inflicting severe damage on its surroundings.

Superheated water released from a closed container at these conditions will not generate a BLEVE, as homogeneous nucleation of vapor bubbles is not possible.

In the case of unignited BLEVEs of liquefied gases, rapid cooling due to the absorption of the enthalpy of vaporization is a hazard that can cause frostbite.

If a flammable substance, however, is subject to a BLEVE, it can ignite upon release, either due to friction, mechanical spark or other point sources, or from a pre-existing fire that had engulfed the pressure vessel and caused it to fail in the first place.

Furthermore, a very significant amount of the escaped fluid will burn in a matter of seconds in a raising fireball, which will generate extremely high levels of thermal radiation.

While tanks are often designed to withstand great pressure, constant heating can cause the metal to weaken and eventually fail.

[13] The main damaging effects of a BLEVE are three: the blast wave from the explosion; the projection of fragments, or missiles, from the pressure vessel; and the thermal radiation from the fireball, where one occurs.

[14] At Feyzin, three of the propelled fragments weighed in excess of 100 tons and were thrown 150–350 meters (490–1150 ft) from the source of the explosion.

One bullet tank at San Juanico travelled 1,200 meters (0.75 mi) in the air before landing, possibly the farthest ever for a BLEVE missile.

"Analysis of Boiling Liquid Expanding Vapor Explosion (BLEVE) Events at DOE Sites" (PDF).

A BLEVE–fireball at the Philadelphia Energy Solutions refinery , as rendered by the CSB
BLEVE mechanism
In this diagram for propane , the orange curve represents its vapor pressure as a function of temperature. The minimum temperature above which a BLEVE can occur is the abscissa of the intersection between the atmospheric pressure horizontal line (blue) and a curve here called the superheat-limit locus . This is roughly a straight line with its upper limit at the gas critical conditions . A liquid expanding along AA' does not cross the superheat-limit locus and will not BLEVE. Conversely, for sufficiently high temperatures, as in the BB' expansion, the superheat-limit locus is crossed and a BLEVE will occur. [ 8 ]