Co2 can intensify narcosis, and cause deepwater blackout in scuba divers. It's the reason everyone used to be so high on "high flow" regualtors- so it would reduce C02 build up on deep air dives. Trimix allows you to use a cheap regulator and still breath easy because of the smaller size of the He atom vs. N2.
I can't imagine anyone using a 10% 02/ 90 %N2 mix at 400' since it would make you loopy as hell at 20'. They we're playing around with helium and hydrogn back then- Max Knoll was making 437' Helium dives in Lake Michigan back in the 30's.
Eric, I have some questions about you inhale dives with lack of narcosis. I know from years of deep air diving that I can "feel" fine with proper breathing, warm drysuit, high flow regulator, and a scooter to drag my butt around, but that doesn't mean I wasn't narked at the time. I used to think I was fine until I did some heliotrox dives on a simple 75' wreck, that I must have over 500 dives on, and saw a lot more details than I ever realized- and thus the reason why we use 100' EAD's on our trimix dives.
I can understand the idea of no narcosis on an exhale dive, but an inhale dive?
It goes against everything I've ever heard of when talking to hyperbaric doc's about this. I'm wondering if your dealing more with a conditioned response under stress rather than real avoidance of narcosis?
Jon
