BLEVE – boiling liquid expanding vapor explosion
This occurs when the pressurized liquid inside of a vessel, such as a propane tank, reaches temperatures higher than that liquid’s boiling point against the ambient temperature. It can also be caused by mechanical damage or overfilling a vehicle, causing an explosion.
When the pressure in a tanker trailer, railcar, or vessel can no longer be contained and mechanically fails and results in an explosion. This is why road tanker safety precautions should be in place. Depending on if the liquid is flammable or not, an explosion will result in a fire.
The two-stage BLEVE
If a container vents combustible vapor into a confined space where it can mix with air in the presence of a source of ignition, it will explode. If the explosion acts as feedback – stressing an already heated container – then a second-stage BLEVE may occur. That is when the containing vessel ruptures and the vapor explodes. Fortunately, most BLEVE events are first-stage. They just make a big bang.
For context, a BLEVE can be a big bang that can destroy a building, a two-stage BLEVE can destroy a city block.