IT is well known that when a hot liquid comes into contact with a cold vaporizable liquid an explosion of considerable violence may occur. This type of explosion is called alternatively a vapour explosion, a thermal interaction or fuel-coolant interaction (FCI), the hot liquid being the fuel and the cold liquid the coolant. These interactions are not the result of chemical change; the energy source is the excess heat in the fuel. Fuel-coolant interactions have been observed between molten tin, indium, steel, aluminium and cold water, in the nuclear field between molten uranium dioxide (the fuel) and liquid sodium (the coolant), and in the chemical industry between liquefied natural gas, LNG (the coolant) and water (the fuel)1. Witte, Cox and Bouvier2, Brauer, Green and Mesler3 and Groenveld4 have given resumes of some proposed mechanisms for FCIs but, as they point out, none of those descriptions is really satisfactory.