Boiling Liquid Expanding Vapor Explosions (BLEVEs) are among the most feared events when tanks of hazardous materials are exposed to fire or physical damage or other events that cause excessive pressures within the tank. A BLEVE could occur when flames impinge upon the vapor space (unwetted internal surface) of the tank where there is no liquid to absorb heat. As the vapor space is heated, the pressure inside the tank (even after the relief valve opens) becomes so great that it eventually vents itself through the weakest area of the tank. As the pressure inside is increasing, the flames weaken the structural integrity of the tank, thus creating the conditions for venting. This sudden venting of pressure and vaporization of product involves the violent rupture of the container, with rocketing fragments. If the container stored a flammable liquid or gas, a large rising fireball will form, the size of which will vary with the amount of hazardous material present. (EPA, Technical Guidance for Hazards Analysis, 1987. p. F-1)