3. Helium

The main characteristics of helium are given in table 1 .

Gas-phase distribution is similar to that of hydrogen, minus the problems of embrittlement. But liquid-phase distribution is justified for two reasons:

• there are very few sources of production: mainly in the United States, with some in Poland; transport to the place of use is extremely long; economically, despite its cost and the insulation problems it poses, the liquid pays for itself in transport savings (dead weight divided by a factor of the order of 6 to 8);

• many uses of helium are in cryogenics (e.g. superconductivity); helium therefore has to arrive in liquid...