<P> Hydrogen has a clean flame and is good for use on aluminium . It can be used at a higher pressure than acetylene and is therefore useful for underwater welding and cutting . It is a good type of flame to use when heating large amounts of material . The flame temperature is high, about 2,000 ° C for hydrogen gas in air at atmospheric pressure, and up to 2800 ° C when pre-mixed in a 2: 1 ratio with pure oxygen (oxyhydrogen). Hydrogen is not used for welding steels and other ferrous materials, because it causes hydrogen embrittlement . </P> <P> For some oxyhydrogen torches the oxygen and hydrogen are produced by electrolysis of water in an apparatus which is connected directly to the torch . Types of this sort of torch: </P> <Ul> <Li> The oxygen and the hydrogen are led off the electrolysis cell separately and are fed into the two gas connections of an ordinary oxy - gas torch . This happens in the water torch, which is sometimes used in small torches used in making jewelry and electronics . </Li> <Li> The mixed oxygen and hydrogen are drawn from the electrolysis cell and are led into a special torch designed to prevent flashback . See oxyhydrogen . </Li> </Ul> <Li> The oxygen and the hydrogen are led off the electrolysis cell separately and are fed into the two gas connections of an ordinary oxy - gas torch . This happens in the water torch, which is sometimes used in small torches used in making jewelry and electronics . </Li>

Result of fire entering the cutting torch at high speed