There are basically two kinds of water vapour explosions, viz. confined and unconfined. Confined ex-
plosions can occur in various situations in industry. Unconfined explosions typically occur when very hot
molten metal accidentally makes contact with water. In order to explain the extremely rapid production
of water vapour that can then occur, “fine fragmentation” of the molten metal must take place. The paper
first presents some early suggestions for the nature of the fine fragmentation process. In more recent
theories the Weber number, We, is used as a measure of expected extent of molten-metal fragmentation
in a given situation. Film boiling plays a central role. Attempts at developing mathematical models of
unconfined water vapour explosions have been made. The next section of the paper is devoted to case
histories of unconfined water vapour explosions. Then various kinds of confined water vapour explosions
are discussed, including water boiler explosions, water vapour BLEVEs, and water vapour explosions in
the paper industry. Some case histories of confined water vapour explosions are also given. The final
section of the paper is devoted to measures for preventing and mitigating water vapour explosions in
industry.