What is a 'BLEVE' and what causes it?

BLEVE (pronounced 'blevee') stands for Boiling Liquid Expanding Vapor Explosion. It occurs when a tank containing a pressurized liquefied gas (like propane, butane, or LPG) is heated — typically by an external fire — to the point where the tank weakens and fails. When the tank ruptures, the suddenly-depressurized liquid flashes to gas almost instantaneously, expanding hundreds of times in volume and igniting in a massive fireball. BLEVE incidents have produced fireballs hundreds of feet across and projectile tank pieces flying half a mile. The reason firefighters evacuate large areas around fires involving propane tanks is BLEVE risk. If you see fire on or near a pressurized gas tank, evacuate widely and immediately.