A BLEVE is an explosion as the consequence of the catastrophic rupture of a pressure vessel containing a liquefied gas. The catastrophic rupture of the vessel in a BLEVE is caused by the sudden isentropic drop of pressure from an initial state of equilibrium to a state, normally at atmospheric ambient conditions, that generates enough superheat to initiate a kind of boiling throughout the bulk liquid called homogenous nucleation.
The temperature at atmospheric pressure above which homogenous nucleation takes place is called the superheat limit temperature. If the temperature in the vessel is above this value, then homogeneous nucleation, a BLEVE, will occur when the contents are isentropically reduced to atmospheric conditions.
(NOTE: this is the primary theory behind BLEVEs, but there is a lot of research into a phenomenon called a Cold BLEVE, with is not dependent upon the concept of a superheat limit temperature.)
In homogenous nucleation, vaporization occurs simultaneously and in microseconds throughout the entire bulk liquid mass. This causes an immediate and explosive failure of the vessel. The contents exit at sonic velocity.
If the gas is flammable and an ignition source is available, a fireball will ensue, with the flame front chasing the sonic fluid front as it expands from the vessel.
The stereotypical BLEVE occurs when a flame impinges on the vapor space of an LPG tank (say, the outlet of a relief valve ignites…) creating a weakness and a temperature rise above the superheat limit temperature. The metal weakens and fails, leading to enough of a pressure drop to initiate homogeneous nucleation, and the BLEVE occurs.
An external fire is not necessary. A CSB investigation of the BLEVE of a reboiler at the Williams Geismer facility in Louisiana found the initial crack and pressure release was due to thermal expansion.
Chemical Safety Board Website. Williams Olefins Plant Explosion and Fire. https://www.csb.gov/williams-olefins-plant-explosion-and-fire-/
Birk. AM, et al., Hot and Cold BLEVEs: Observation and Discussion of Two Different Kinds of BLEVEs, AIChE Symposium Series, vol. 8, 1993 .
Mengmeng, Xie, Thermodynamic and Gas Dynamic Aspects of a BLEVE, Delft University of Technology, The Netherlands, October 1, 2007.
Mannan, S, Lees' Loss Prevention in the Process Industries, Section 17.29 Boiling Liquid Expanding Vapor Explosions, 4th ed., 2012.
Center for Chemical Process Safety (CCPS). Guidelines for Vapor Cloud Explosion, Pressure Vessel Burst, BLEVE and Flash Fire Hazards, 2nd ed.; John Wiley & Sons, Inc.: Hoboken, New Jersey, 2010.
US Chemical Safety Board
Sent: 09-04-2020 10:36
From: Marlon Guerra Mutis
Subject: Open discussion: BLEVE vs. BOILOVER
Some experienced / technical thoughts / references about differences between BLEVE and BOILOVER, and conditions to define the classification of such events are welcomed.