Elgas LPG Gas Blog

BLEVE - LPG-Propane Gas Bottle Explosions - LPG Cylinder Blasts

A BLEVE - Boiling Liquid Expanding Vapour Explosion - is a gas explosion caused by the rupture of a pressurised containment vessel. This is when its contents boil and the pressure builds, exceeding the design pressure of the vessel. A BLEVE blast does not necessarily involve fire, a prime example of this being a steam boiler explosion.

The BLEVE gas can be anything from LPG-propane, to acetylene welding gas, to the steam in a steam boiler.

The common element of a BLEVE is typically a steel vessel that ruptures when the contents boil and pressure builds beyond the containment limits of the vessel.

BLEVE gas explosion

BLEVE - Boiling Liquid Expanding Vapour Explosion

BLEVE from a gas tank explosionAn LPG tank explosion is sometimes referred to as a BLEVE. BLEVE is the acronym abbreviation for Boiling Liquid Expanding Vapour Explosion.

If a pressurised gas bottle or vessel ruptures when the contents are above their boiling point, it is referred to as a BLEVE. 

LPG (propane) bottle and tanks rarely BLEVE because of the Pressure Relief Valve that releases the excess pressure, preventing a rupture.

A large BLEVE is typically at a commercial or industrial site, where there are large storage vessels.

The Anatomy of a BLEVE - What Causes a BLEVE or Explosion

A BLEVE is caused by a pressure build-up that exceeds the strength of the steel vessel walls and causes it to rupture with bomb-like force. The escaping gas rapidly expands, with explosive force, from the rupture and may or may not involve fire.

For example, if the BLEVE was caused by steam, the steam would not catch fire, even though it exploded violently.

On the other hand, a hydrocarbon fuel, like LPG (propane), would rapidly expand and would typically encounter an igntion source, causing an incendiary fire ball.

Pressure Relief Valve for LPG Propane Tanks Prevents BLEVE Explosions

Pressure Relief Valve for LPG Propane Tanks & Cylinders Arguably, the single most important safety feature of a gas bottle or propane tank is the Pressure Relief Valve. It’s actually a propane safety valve within a valve. The Pressure Relief Valve is incorporated into the main gas valve on the gas bottle (propane tank), as shown in the accompanying picture. 

If the pressure of the gas inside the bottle increases, as the result of a fire or other heat source, the pressure relief valve releases some of the gas from the propane tank to relieve the pressure. 

No pressure build up means no risk of a BLEVE or LPG tank explosion. 

Steam boilers also have pressure relief valves for exactly the same reason. The only difference is that it is independent of any other valve,

Gas bottles have been around for about 100 years.

Over that time, the gas industry has had a lot of time to perfect the safety features of gas bottles and valves.

In yet another episode of MythBusters, they tried to see if a BBQ gas bottle would turn into an exploding rocket when placed in a fire.  

They placed the bottle in the middle of a raging fire, burned down the demonstration building. 

After it was over, the gas bottle was still sitting there, looking almost brand new. 

It only proved that the Pressure Relief Valve worked perfectly.

A Gas Explosion is Rarely a Gas Cylinder Explosion

BLEVE from exploding propane

A gas explosion is almost always caused by the accumulation of leaking gas in an enclosed space, not an LPG tank explosion. The leak can be from the gas appliance or other source not involving the bottle. In many cases, when a gas explosion occurs, the gas bottles are not even involved.

The LPG tanks almost never explodes because of the built in Pressure Relief Valve.

Many gas explosions are caused by natural gas (piped gas), not bottled gas.

The gas involved in an explosion may also be welding gas or other non-LPG gas.

There must be an ignition source for an explosion to occur.

Tradespeople Incidents with Other Gases

Explosions involving tradespeople are typically welding gas related.

Acetylene gas used in oxy acetylene welding, which is very volatile, is frequently the culprit.

Pictures of a completely destroyed plumber’s truck are almost assuredly acetylene related.

Acetylene gas explosion

Pictured above is the result of an acetylene explosion in a tradie's van.

However, the media just reports “gas bottle explosion” without specifying the gas.

The result is that many people falsely assume it was an LPG tank explosion.

BLEVE from gas explosion

Final Thoughts

While unquestionably spectacular, fortunately BLEVEs are quite rare.

Storage vessels are designed with a number of safety devices including pressure relief valves, deluge systems that shower water on the vessel to keep it cool and burying the vessels underground.

So, the danger of being affected by a BLEVE are way less than being struck by lightning.