"In the book it mentioned that after the tragic Apollo 1 fire, a lot of changes were made to the apollo spacecraft by the astronauts. One of these was that they quit using 100% oxygen as a breathable atmosphere and started using a 60/40 mix of Oxygen/Nitrogen. My question is why didn't they use a 60/40 mix of oxygen/helium like divers use? It seems to me that it would be advantageous to use helium because the helium (as its been explained to me, I'm no expert) enters and exits the bloodstream quicker than nitrogen which makes the 'bends' no longer an issue. Helium is inert so it makes it a good substitute for nitrogen.

They did mention in the book that Helium has the lowest boiling point of all the gases they were carrying. In fact the helium tank blew up when they fired up the LEM's engines the last time. My guess is they didn't want to carry too much because of the fear of it boiling and blowing up the bottle when it got too hot. But that's just a guess, does anybody know the official reason."

Bad PR. Didn't want astronauts talking in high voice.
-gb