In Reply to: More nitrox/air dual use: The PSI standards posted by Ken Kurtis on August 26, 2005 at 11:42:40:

That does sound old school. Years ago, if you wanted to dive Nitrox you had to have a special/separate tank clearly marked and kept oxygen clean. Your reg was supposed to be "O2 Clean" if I remember also

In the old school, nitrox was "mixed" by partial fill pressures in the tank. Present day membrane systems don't expose the tank to more than 40% O2 (and usually less) due to the fact that you can't really go very deep on 40%.

Maybe they should call nitrox membrane system blends of less than 40% "reduced nitrogen content air". It would eliminate some comfusion. :)