Posted by Bob3 on March 23, 2001 at 09:49:49:
In Reply to: Why not 40% O2 and 60% He? posted by AADIVER on March 23, 2001 at 07:37:29:
It all comes down to the bottom line, $$$.
Helium isn't cheap, so unless you've got deep pockets, a little nitrogen won't hurt.
The normal switchover depth to mixed gas is considered 180 ft. (commercial divers & USN)
You gain a hair extra deco obligation with He