Boiling liquid expanding vapor explosion
The BLEVE ( boiling liquid expanding abbreviation of vapor explosion ) is a gas explosion in a boiling liquid expanding. BLEVEs may arise in closed tank containers containing flammable liquid or liquefied substances / substance mixtures.
The reaction is in the first phase with a boiler explosion physically similar, except that at a BLEVE instead of water the substance is combustible liquid in the tank that explodes upon exit.
Process
If a tank vessel with a flammable liquid enclosed from the outside, for example by a fire (fire accident), so the flames heat the container wall. The heat is transferred through the metal wall of the tank liquid is beginning to boil. This causes the pressure in the tank increases more and more. While the wall is cooled by the boiling liquid tank, the metal is prevented from softening or melting. Everything remains initially stable until then.
Reaches the vapor pressure of boiling liquid in the tank, the triggering threshold of the relief valve, which is located on top of the tank, the gas rushes through the valve up to the air. If it has not already ignited when flowing by itself, then this is the concern surrounding fire quickly and reliably. Thus, a huge jet of flame or torch burning liquid vapor is generated, while inside the liquid level rapidly decreases during Ausströmungsvorganges from the pressure relief valve.
If, however remains less liquid in the tank, less container can be cooled by the low-lying liquid level. The consequence is that the tank wall heats up more and more by the surrounding fire, which more liquid vapor pressure is built up, which can no longer be discharged through the valve. The already overheated and weakened by the fire walls of the tank begins to balloon by the enormous pressure to soften and eventually burst. The now leaving huge amounts of gas and the boiling liquid ignite immediately, and there is a huge explosion with a huge fireball, raining from the still liquid, burning droplets down, which can lead to secondary fires in the area. In addition, with flying debris of the tank that fly as a deadly projectiles into the environment can be expected.
Typical Bleve events in steel containers occur at temperatures above 538 ° C ( decreasing strength of the steel container with increasing temperature), with residual quantities of 50% or less and within 8-30 minutes after fire outbreak on.
The effects of such a BLEVE event are extraordinary: When rupture of a filled with liquid propane tanks, a 1300 kg 80 m high and 50 m wide fireball was observed. The wreckage of the tank flew far up to 500 m.
From the above it follows that the most effective method for preventing a BLEVE is to fill the affected tank before the outbreak of fire from the inside with a fine calf- shaped aluminum mesh, rolled in the form of cylinders (eg EXESS ) and protect it. This network distributes the aluminum heat so much that the temperature and pressure required for an explosion can not be achieved. In a non- protected with this aluminum mesh tank, it stays cool with water only, on the one hand to minimize the temperature increase in the interior and to prevent softening of the tank wall. These very large amounts of fluid are necessary, especially for larger tanks.
So there are, according to the Hesse state fire school the required amount of water for the cooling alone -containing by burning LPG gas cylinders and LPG vehicles per 15 liters / min, private LPG tanks 180 liters / min, truck - trailer trucks per 1,200 liters / min, tank cars 2,500 liters / min and large memory or LPG tankers eventually up to 150,000 liters / min.
If these amounts of water are not available, and this is in fires large amounts of memory is often the case, BLEVE events are not controllable.
Accidents
Larger loss events with BLEVEs occurred: