Helium

Add another Use that has often been referenced. Helium is used as a mix with air in scuba tanks for deep dives to lessen the proportion of oxygen.

See this link:
http://www.pa.msu.edu/sciencet/ask_st/082593.html

Thanks for the great web page - SCSmith

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Helium is not primarily used

Helium is not primarily used as an oxygen substitute as much as a nitrogen substitute. You do have to worry about oxygen toxicity issues. In situations where atmospheric pressure is increased nitrogen has anaesthetic qualities. Above about 4 atmospheres divers experience nitrogen narcosis.

You also have problems with increased absorption of nitrogen in various tissue compartments. Some tissues absorb and release gasses at different rates. The longer you are down and deeper you are the more various gasses increase their solubility. As you return to surface atmosphere Nitrogen slowly leaves your tissues and can collect and create bubbles large enough to cause physiological problems (the bends).

One solution to the bends is to slowly return to the surface with timed safety stops to allow nitrogen to come out of solution more gradually so you can naturally eliminate it through breathing.

The other solutions that have been tried include increasing the amount of oxygen (Nitrox). This decreases issues with the bends and nitrogen narcosis, but increases the risk of oxygen toxicity at deeper depths.

Divers have also substituted helium (Tri-mix) and hydrogen for nitrogen with varying degrees of success. The helium seems obvious, its inert and is release from solution much more quickly than nitrogen.

The hydrogen sounds idiotic, but is only flammable in the presence of high enough concentrations of oxygen. At extreme depths you can decrease the amount of oxygen below the level of flammability and substitute nitrogen or hydrogen (This is not at all common). Its been quite a long time since I read about this but there was only really one or a few divers to try this but they were successful in diving to I think about 2000ft of sea water with around 4%oxygen and a hydrogen blend. The details are kind of rough in my brain..

Jason

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