28% O2 vs. 32% O2: What a Difference

[Rick Palm]

As a result of inattention on my part, I ended up with a fill of 28% Nitrox, instead of the usual 32% I've breathed for years. I dived it at Ginnie today, and noticed a palpable difference in nitrogen narcosis as evidenced by increased anxiety. I also incurred a significantly longer decompression obligation. It's tempting to go back to partial pressure fills for a 36% mix, still under 1.6 PO2 for the local popular spots, but necessitating a closer eye on the CNS clock.

[fixxervi6]

I've never noticed a difference in narcosis, I narc about the same on 32 as I do on air.

I can't imagine 4% would make any noticiable difference, what about other factors, fatigue, increase in flow/work, different reg etc etc.

I'm also in the camp that o2 has narcotic effects

just my observations and opinions, I'm not paid to know these things.

[chimie007]

IMHO pushing the PO2 in high flow cave is asking for trouble.

[Dark Eternal]

I've never noticed a difference in narcosis, I narc about the same on 32 as I do on air.

I can't imagine 4% would make any noticiable difference, what about other factors, fatigue, increase in flow/work, different reg etc etc.

I'm also in the camp that o2 has narcotic effects

just my observations and opinions, I'm not paid to know these things.

I don't narc easy but my wife does. At 90' in a cave on air, she should not be there. She is 100% fine on 32%. It makes a lot of sense - less nitrogen being absorbed = less narcosis effects. From what I understand while oxygen does have narcotic effects it is significantly less at the shallower depths that most divers are operating at. There is absolutely zero science behind my observations but the results are very real for her at least.

[FW]

IMHO pushing the PO2 in high flow cave is asking for trouble.

I agree!! The reason 32% is standard in Cave Country now is because of an accident at Devil's Eye. The standard back then was 34%. Someone had a little too hot mix, around 36%, and toxed.

[Captain Bil]

IMHO pushing the PO2 in high flow cave is asking for trouble.

That's the kicker. PO2 of 1.6 is not smart at depth in a high flow environment and is not worth the little difference that 4% might make. The working portion of your dive should never be higher than 1.4 PO2, IMHO.

[bletso]

As a result of inattention on my part, I ended up with a fill of 28% Nitrox, instead of the usual 32% I've breathed for years. I dived it at Ginnie today, and noticed a palpable difference in nitrogen narcosis as evidenced by increased anxiety. I also incurred a significantly longer decompression obligation. It's tempting to go back to partial pressure fills for a 36% mix, still under 1.6 PO2 for the local popular spots, but necessitating a closer eye on the CNS clock.

Perhaps it was the anxiety of diving a new mix that was the trip. Keep the PO2 low as practical. Don't kid yourself, one day a high PO2 might just clean your clock. FWIW, a few years back, we did some tests at 42MSW switching between Nx 5/95, air, and Nx 36/64. There was no discernible difference in the narcosis level between them!! A little more deco won't hurt you unless you dive dry w/o a pee valve.

Dive Safe

Dale

[Howard]

You don't want to be increasing the O2 content to lower N2 %. You will eventually kill your self and possibly your buddy doing this. (assuming you find a buddy that will dive a plan like that with you).
Use helium to decrease narcosis. Bottom line.

[Kelly Jessop]

12 years ago 36% (and even 38%) was the norm at Ginnie,but fortunately we got a lot smarter. There is too much CO2 build up to justify high PPO2 in a high flow cave system

[Sludge]

Never underestimate the power of suggestion. Not to disparage anyone, but if you think you'll be less narced, you'll probably feel less narced.

When nitrox made its way into the recreational realm in the mid-90s, there were a number of "benefits of nitrox" touted. You'll feel less tired after a dive. You'll feel less cold during a dive. You'll be less narced during a dive. As time went by, each of these were disproved in blind tests.

The only proven benefit of nitrox is shorter decompression time/longer no-decompression time. As was mentioned, the standard nitrox mix in cave country used to be 34%. Now it's 32%, and I have started using 31% in Jackson Blue. The extra several minutes of deco is worth it to keep the PO2 a couple of points lower. I'm old, and I want to get older.