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Uploaded on Feb 6, 2010
Under rapid heating (for example, from a pool fire engulfing the tank), a tank containing pressurized liquid may fail suddenly producing an explosive effect. The liquid in the tank absorbs energy from the surrounding fire and heats up rapidly. The resulting increased rate of vaporization produced increases the ullage pressure. When this pressure exceeds a certain limit (characteristic of the material properties of the tank wall, wall thickness and temperature), the tank fails. The liquid released from the tank boils rapidly and expands. The resulting explosion may fragment the tank into pieces and propel them over large distances. If the hazmat is flammable, it may ignite and form a fireball posing additional hazard. This phenomenon is called a BLEVE or Boiling Liquid Expanding Vapor Explosion.
BLEVE accounts for the following key coupled processes: * heat transfer: - from flame to tank - from tank walls to the liquid and vapour phases - between liquid and vapour phases * thermodynamic transformations within the tank and pressure build-up * activation of pressure relief valve (or PRV) and venting * wall stresses and material property degradation * tank failure * depressurization of liquid upon tank failure with concomitant thermodynamic transformations