Quote Originally Posted by EricR
The reason people use helium is so they can do deep dives to 250 feet plus and not experience the toxic effects of O2 at that depth. Also at shallower depths say around 180 feet helium is great because you do not experience the narcotic effect O2 gives you at that depth. Something that is kind of important if you are working at depths.
Hah!! My chance to jump on someone for an obvious error.

O2 is narcotic at .... ? Maybe so, but I don't think it would be a good idea to replace ALL of it with helium. Replacing the avaliable nitrogen (N) with helium (He) - and leaving the oxygen alone might work well.

Where are the smilies ... got 'em ... :P