Boiling liquid expanding vapor explosion

A boiling liquid expanding vapor explosion (BLEVE,  /ˈblɛviː/ blev-ee) occurs when a vessel containing a pressurized liquid above its boiling point ruptures.[1]

Contents

Mechanism

If a vessel partly filled with liquid with vapor above filling the remainder of the container, is ruptured—for example, due to corrosion, or failure under pressure—the vapor portion may rapidly leak, lowering the pressure inside the container. This sudden drop in pressure inside the container causes violent boiling of the liquid, which rapidly liberates large amounts of vapor. The pressure of this vapor can be extremely high, causing a significant wave of overpressure (an explosion) which may completely destroy the storage vessel and project fragments over the surrounding area.

While the term BLEVE is most often used to describe the results of a container of flammable liquid rupturing due to fire, a BLEVE can occur even with a non-flammable substance such as water,[2] liquid nitrogen[3] liquid helium or other refrigerants or cryogens, and therefore is not usually considered a type of chemical explosion.

Fires

BLEVEs can be caused by an external fire near the storage vessel causing heating of the contents and pressure build-up. While tanks are often designed to withstand great pressure, constant heating can cause the metal to weaken and eventually fail. If the tank is being heated in an area where there is no liquid, it may rupture faster without the liquid to absorb the heat. Gas containers are usually equipped with relief valves that vent off excess pressure, but the tank can still fail if the pressure is not released quickly enough.[1]

If the substance involved is flammable, it is likely that the resulting cloud of the substance will ignite after the BLEVE has occurred, forming a fireball and possibly a fuel-air explosion, also termed a vapor cloud explosion (VCE). If the materials are toxic, a large area will be contaminated.[4]

Incidents

In August 1959 the Kansas City Fire Department was hit with their largest loss of life in the line of duty deaths to date, when a 25,000 gallon gas tank exploded during a fire on Southwest Boulevard killing five firefighters. This was the first time BLEVE was used to describe a burning fuel tank. Significant industrial BLEVEs include accidents at Sunray, Texas in 1956, Glasgow, Scotland in 1960, Feyzin, France in 1966; Crescent City, Illinois in 1970; Kingman, Arizona in 1973; Texas City, Texas in 1978; Murdock, Illinois in 1983; and San Juan Ixhuatepec, Mexico City in 1984.[5] In 1978, a BLEVE occurred after a traffic collision involving a LPG truck in the Los Alfaques disaster in Spain.

Safety measures

Some fire mitigation measures are listed under liquefied petroleum gas.

See also

References

  1. ^ a b Trevor Kletz (1990) Critical Aspects of Safety and Loss Prevention, Butterworths (London) ISBN 0-408-04429-2 pp 43-45
  2. ^ "Temperature Pressure Relief Valves on Water Heaters: test, inspect, replace, repair guide". Inspect-ny.com. http://www.inspect-ny.com/plumbing/Water_Heater_Relief_Valves.htm. Retrieved 2011-07-12. 
  3. ^ "Nitrogen Dewar Explosion at Texas A&M University". http://www.thebatt.com/2.8485/chemistry-lab-explosion-costly-1.1195774. 
  4. ^ "Chemical Process Safety" (PDF). http://chemelab.ucsd.edu/processdesign/safety/safety-notes.pdf. Retrieved 2011-07-12. 
  5. ^ "PEMEX LPG Terminal, Mexico City, Mexico. 19th November 1984: Accident summary". www.hse.gov.uk. 1984-11-19. http://www.hse.gov.uk/comah/sragtech/casepemex84.htm. Retrieved 2011-07-12. 

External links