About a year ago there was a long electronic discussion of nitrogen and scuba diving on the chemical education listserver. It turns out to be complicated. There are actually two effects. The first is the dissolved gases coming out and leading to the "bends." Apparently solubility in fat tissue also plays a role in this and the effect is not limited to nitrogen. Scuba divers must decompress slowly on the way up even if they breathe oxygen-helium. The reason for using helium instead of nitrogen is a separate effect called "nitrogen narcosis" or "rapture of the deep," which causes one to lose contact with reality. Under this influence a diver at depth may, e.g., become convinced that he can breathe without his gas tank and proceed to remove it. Anyway, it turns out that very few general chemistry textbooks explain all of this properly.
L. Peter Gold
Department of Chemistry
Penn State University