craziness. >> enormous blast is the result of the fire melting the steel surrounding the tank, followed by the massive release of propane. the explosion is called a blevy. >> a blevy is a boiling liquid expanding vapor explosion. the steel will weaken because of the heating and because of the pressure inside, it ruptures and that pressurized gas is released very, very quickly. >> the fire department tries to keep the other tanks from exploding by cooling them with water. >> we put the water where the flame is impinging on the steel to keep that steel cool so it won't fail. you're controlling the fire, not really putting it out. >> authorities evacuate the neighborhood, close highways and air space and pump water for 15 straight hours. >> we just phone down to the water pumping stations, have them increase the pressure for us because we're using such large amounts of water.