steam explosions are not normally chemical explosions, although a number of substances react chemically with steam (for example, zirconium and superheated graphite react with steam and air respectively to give off hydrogen, which burns violently in air) so that chemical explosions and fires may follow. some steam explosions appear to be special kinds of boiling liquid expanding vapor explosion (bleve), and rely on the release of stored superheat. but many large-scale events, including foundry accidents, show evidence of an energy-release front propagating through the material (see description of fci below), where the forces create fragments and mix the hot phase into the cold volatile one; and the rapid heat transfer at the front sustains the propagation.