How a BLEVE occurs
A BLEVE is the catastrophic rupture of a vessel containing a liquid superheated relative to the external pressure. Upon sudden release, part of the liquid vaporises and expands very rapidly. The event can generate a pressure wave and project vessel fragments over a distance.
Related concept: Pressure equipment.
A fireball is not always present
A BLEVE is a physical event and does not itself require combustion. If the contents are flammable and ignite, a fireball with intense thermal radiation may occur. Keeping this distinction clear helps avoid overlooking vessels whose contents do not burn but store hazardous energy.
Nor is every tank explosion a BLEVE. Identifying the mechanism requires knowledge of the contents’ state, pressure, temperature and the way the vessel ruptured.
Scenarios to consider
An external fire can heat a vessel and weaken its walls, particularly in areas not cooled by the liquid inside. Other conditions may also reduce strength or bring the contents into a hazardous state.
The assessment combines design, location, fire protection, maintenance and relief systems. A safety valve may control certain overpressure scenarios, but it does not demonstrate that the shell retains sufficient strength under every thermal exposure.
Prevention and preparedness
Measures are defined from the design stage: limiting inventories where feasible, separating sources of danger, protecting equipment and ensuring appropriate inspections. Emergency access, exposed areas and the possibility of an event affecting nearby facilities must be considered.
Responding to a vessel heated by fire is a task for specialist personnel under the emergency plan. An approach to inspect it or attempt an operation must not be improvised without assessing how the scenario may develop.
Hypothetical example
A liquefied-gas tank stands beside a traffic area. A review finds that a modification has brought combustible materials closer to it. The team studies the new fire scenario, removes the incompatible condition and reviews protective and emergency measures. The review focuses on the changed exposure even though the tank retains its certificates.
Limits of estimates
Effect distances depend on the substance, quantity, conditions and surroundings. A generic distance should not be used as a guarantee of safety. Consequence assessment requires suitable methods and specialists. Simplified models provide support within their scope and must state their assumptions and limitations.
