BLEVE

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 vapor phases
  • between liquid and vapor phases
• thermodynamic transformations within the tank and pressure buildup
• 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

Model Inputs

• tank geometry and tank wall thickness
• tank wall material properties such as density, heat capacity, temperature dependence of the yield strength
• properties of the hazmat such as molecular weight, density, heat capacity of liquid and vapor phases as functions of temperature, vapor pressure as a function of temperature
• vent conditions such as the settings on the Pressure Relief Valve (PRV) and the vent diameter
• characteristics of external source that initiates BLEVE (For example, if a fire initiate it, the dimensions of fire, flame temperature and the proximity of flame to the tank)

Model Outputs

• occurrence and time for tank failure
• venting rate and temperatures of various zones in the tank as functions of time
• occurrence of a BLEVE
• Blast strength associated with BLEVE
• Blast strength at various receptor locations