What firefighters need to know about BLEVEs
Here's a breakdown on what a boiling liquid expanding vapor explosion is, how it occurs and how it can be prevented
By Shelbie Watts, FireRescue1 Editorial Assistant
In 1959, the Kansas City Fire Department suffered its second largest loss of life in the line of duty when a 20,000 gallon gas tank exploded in a fire, killing five firefighters. This kind of dangerous explosion would later come to be known as a BLEVE, but what exactly does that mean?
Here's a breakdown of what a BLEVE is, how it occurs and how it can be prevented.
What is a BLEVE?
A BLEVE is a boiling liquid expanding vapor explosion, which occurs when pressurized liquid inside of a vessel, such as a propane tank, reaches temperatures higher than that liquid’s boiling point. If the vessel can no longer contain the pressure inside of the sealed tank due to the high temperatures, it will mechanically fail, causing the explosion.
Whether or not a fire occurs is contingent on if the liquid inside of the tank is flammable. If it is, a fire will often occur. If the vessel contains non-flammable liquid (such as a steam boiler), a BLEVE will occur, but the vapors will not ignite.
Heat does not have to be present for a BLEVE to occur. Mechanical damage or overfilling can also cause the vessel to explode.
A second-stage BLEVE can occur if a vessel releases combustible vapor into an area where it then mixes with air in the presence of a source of an ignition. Then, the explosion can stress the heated vessel and cause it to rupture, resulting in an explosion of the vapor.
How can a BLEVE be prevented?
The complete rupturing of a vessel can be prevented by incorporating a sort of vent mechanism to let vapors eject directly up into the atmosphere.
If the vapor is not able to be ejected straight up, the pressurized vessel should be kept in an enclosure that will contain any explosion pressure and control the blast.
Firefighter safety in BLEVE-possible situations
When battling a propane tank fire or another type of incident where a BLEVE is possible, NIOSH recommends firefighters do the following:
- Keep as much distance from the fire as possible by using unmanned hose holders or monitor nozzles.
- Flood containers with large quantities of water to cool them until well after the fire is out.
- Avoid icing by not directing water at the source of a leak.
- Be aware of sections of the vessel flying in all directions.
NIOSH also urges fire departments to continue to educate its firefighters on the dangers of BLEVEs so they can be aware and stay safe at high-risk scenes.