Nitrox: Narcosis myth?

[elmo]

Here's a thought experiment (i.e. all numbers are made up)

Lets say N2 becomes noticeably narcotic at a PP of around 3 bar (air at 30m)
Lets say O2 becomes narcotic at say 1.6 bar. (twice as narcotic)

Diver at 30m on air has N2 at 3 bar causing narcosis, O2 is at 0.84 so no effect yet.
Same diver on 30% has O2 at 1.2, causing little to no narcosis. N2 is at 2.8 so no N2 narcosis.

The big question would be if narcosis is cumulative i.e. add O2 effect and N2 effect or whether they are acting separately.

The same way we treat He and N2 separately with deco, does that translate to the narcotic effects?

The on-gassing and off-gassing of He and N2 are considered separately, but when it comes to calculating the maximum tolerable gradient, which determines your decompression ceiling, the partial pressures of He and N2 in tissues are considered together (weighted according to parameters). This is true for both Buhlmann and VPM calculations; and probably other mixed-gas models too.

The assumption that N2 and O2 are roughly equally narcotic is typically applied to mean that to determine the narcotic effect of a gas, you consider the total ppN2 + ppO2 combined, and don't distinguish between them.

 

[The Chairman]

On the light side, I often will have fun with people's ignorance. It's just my nature, I guess. While waiting to get on the plane to Anthony's Key, I heard a couple discussing the new movie "47 Meters". One asked the other "I wonder why they called it 47 meters". To which I remarked in an insider whisper: "You get the bends at 48 meters! Every diver knows this!" and walked away. While I was saying this in jest, it reminded me how many divers just have to give an answer, even if they don't know the facts. We live in a society where knowledge is power. The more knowledge you seem to possess, the more powerful you appear to be. This exaggerates myths as the teller regurgitates them with a knowing nod of their head and then they expound on that, making them more outrageous. It's OK to question our assumptions and to discard them when we find them to be not as factual as we once thought. There are a lot of myths in diving including one I heard from my AOW student yesterday: a mask on your forehead is a certain sign of distress. I asked him if that applied to sunglasses since there were two people in the class wearing them like that! I don't think he noticed them, even then.

So just remember: Don't go to 48 meters, or you'll get bent!

 

[uncfnp]

Here's a thought experiment (i.e. all numbers are made up)

Lets say N2 becomes noticeably narcotic at a PP of around 3 bar (air at 30m)
Lets say O2 becomes narcotic at say 1.6 bar. (twice as narcotic)

Diver at 30m on air has N2 at 3 bar causing narcosis, O2 is at 0.84 so no effect yet.
Same diver on 30% has O2 at 1.2, causing little to no narcosis. N2 is at 2.8 so no N2 narcosis.

This is my thought too. And the post by Boulderjohn and the linked article would seem to suggest that the partial pressure of oxygen does not reach narcotic effects until quite high, oxtox high. So it seems reasonable to assume that there could be a very slight decrease risk of narcosis on nitrox.

I am from the camp that was taught, at least informally, that nitrox is less narcotic.

 

[kelemvor]

The problem is that although you can test for nitrogen's effect in a chamber by maximizing the dose, you can't do it with oxygen because of toxicity, so it remains an assumption.

Please elaborate, as I don't understand why they couldn't do that. It seems like all they'd need to do is simulate a 100' dive. With air, there's a good chance the subjects would be experiencing some narcosis. If O2 is as or more narcotic than nitrogen then couldn't they just switch to a gas mix with helium to bring pp02 back to 1 and then compare narcosis to the same dive with 39% or 40%

I must be completely misunderstanding something.

 

[Steve_C]

should not be hard to test. Take several divers. Ideally a mix of ages, experience, and sex. Give them a tank but do not tell them what is in the tank. Some tanks are Air and some are 32%, Take them to 100 feet and run some tests both tests and tasks. These are timed. Computers set to air for NDL. Tests administered by a diver who also does not know which gas they are diving. After the dive give them a written test about what they did on the dive. Again by folks who do not know the mix. Afterwards data is analyzed. Ideally the fill of the tank is totally unknown to anybody but the result analyzers and the fill station folks.

Would be interesting.

It is also possible that the fact they are being tested affects their alertness. At 100 ft I am much more conscientous about some things because I know I am a bit narced.

-Amusing variant if you have enough money and volunteers is to run the same experiment again but tell them what is in the tanks and see if there is a psychological affect of knowing you are diving X.

 

[Saniflush]

So just remember: Don't go to 48 meters, or you'll get bent over!

Fixed that for you

 

[Rhone Man]

Part of the issue is labelling.

A number of people suggest pushing towards calling it "inert gas narcosis" rather than nitrogen narcosis for this reason (as well as being a more accurate label).

 

[MaxBottomtime]

I took this on the UB88. It sits in 182-190'. I was diving on air this particular dive. I have more than 150 dives below 160' on air including several below 200'. I've never forgotten a second of those dives. I've had a clearer head on trimix but my memory was not effected by deep air. I believe anyone telling you they don't remember parts of dives at 120' is either internet myths or someone giving you a load of crap.

 

[northernone]

View attachment 414848
I took this on the UB88. It sits in 182-190'. I was diving on air this particular dive. I have more than 150 dives below 160' on air including several below 200'. I've never forgotten a second of those dives. I've had a clearer head on trimix but my memory was not effected by deep air. I believe anyone telling you they don't remember parts of dives at 120' is either internet myths or someone giving you a load of crap.

Equally humorous are the studies where they give participants non alcoholic beverages and the social conditioning results in intoxicated behavior.

I have been badly narced at 60ft, but I agree with your perspective and don't experience deep air a debilitating mix personally either.

 

[Chavodel8en]

I don't think the appropriate lingo has filtered out to everyday divers.

I still think of it as "nitrogen narcosis," as that was the term I learned when I trained 10+ years ago.

And despite everything, I will probably continue to think of it as "nitrogen narcosis" -- just through force of habit.

I'll try to refer to it as "narcosis" from now on.

Maybe "depth narcosis" or "pressure narcosis" are better terms. After all, those are the decisive factors causing the narcosis. I mean I breath oxygen & nitrogen all day and Im still fairly clear-minded -- well, most of the time.