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.

[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.

[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.

[fixxervi6]

I think that 99% of felt nacrosis is state of mind, if you go in thinking, I"m on 32 I won't narc as much, you won't, if you go in on air thinking, damn I'm gonna narc, your gonna narc. I've seen people totally go blitzo at 80 feet on nitrox - and it was their state of mind that did it to them, you can tell who is gonna freak before you even get in the water sometimes.

Usually its the hoovers (from what I've observed) that narc out to the point you have to grab them because their pupils do that cartoon thing, so my non professional opnion about that is, they are hoovering due to discomfort/anxiety mix that with a touch of narcosis and flipzoid

I can tell "something is up" as shallow as 60 feet, my complex mental math skills (not that I have many to start with) start to be affected around 60 feet, when I get to 90 - 100 ish I can tell when I've hit the depth just by "how I feel".

Around 150 feet my motor skills start getting impacted, so I've decided that was my max depth on air that I would do, ever, just because my hands don't work as well, I have to move real slow working clips etc so I figure thats deep enough, espeically with helium now.

On trimix I count o2 as narcotic, my buddy I dive mix with doesn't.

I've dove 30/30 in Devils and I thought it was a perfect mix for the dive

Dark Eternal - I'd be curious how your wife would feel if you slipped her some 21 and told her it was 32 obviously not a good idea, but the results would be interesting, it would rule out the placebo affect.

First time I took my wife down to 120 on air in a nasty lake, I asked her how she did when it was over, she was like, everything was fine I couldn't tell a difference, I said, thats becase you were narcin, if you are at 120 and you "are not narcing" and feel 100% normal, that means your narced

[Dark Eternal]

I think that 99% of felt nacrosis is state of mind, if you go in thinking, I"m on 32 I won't narc as much, you won't, if you go in on air thinking, damn I'm gonna narc, your gonna narc. I've seen people totally go blitzo at 80 feet on nitrox - and it was their state of mind that did it to them, you can tell who is gonna freak before you even get in the water sometimes.

Usually its the hoovers (from what I've observed) that narc out to the point you have to grab them because their pupils do that cartoon thing, so my non professional opnion about that is, they are hoovering due to discomfort/anxiety mix that with a touch of narcosis and flipzoid

I can tell "something is up" as shallow as 60 feet, my complex mental math skills (not that I have many to start with) start to be affected around 60 feet, when I get to 90 - 100 ish I can tell when I've hit the depth just by "how I feel".

Around 150 feet my motor skills start getting impacted, so I've decided that was my max depth on air that I would do, ever, just because my hands don't work as well, I have to move real slow working clips etc so I figure thats deep enough, espeically with helium now.

On trimix I count o2 as narcotic, my buddy I dive mix with doesn't.

I've dove 30/30 in Devils and I thought it was a perfect mix for the dive

Dark Eternal - I'd be curious how your wife would feel if you slipped her some 21 and told her it was 32 obviously not a good idea, but the results would be interesting, it would rule out the placebo affect.

First time I took my wife down to 120 on air in a nasty lake, I asked her how she did when it was over, she was like, everything was fine I couldn't tell a difference, I said, thats becase you were narcin, if you are at 120 and you "are not narcing" and feel 100% normal, that means your narced

It actually happened the other way around. Every time she had been past 90' on 21 she had gotten narced. We were at JB and at the end of the dive she was like "I was not narced at all - that was a great dive" She thought she was breathing 21 but had in fact had grabbed the tank with 32%. I guess there is an argument for labeling your tanks better than we did. Like I said - not scientific at all but now she only dives 32% in the mill pond and is fine. Maybe its placebo - but it works for her. Personally I cant tell a difference between air and 32% up to MOD of the 32%.

[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.