Nitrox questions

[UWSojourner]

I just finished my Nitrox cert and still have two questions that didn't seem to get definititive answers.

1) Let's say you're diving at 90ft with EAN36. Your equivalent air depth is about 67 ft. I understand that your no-deco time is then based on 67 ft, but is your nitrogen narcosis also going to be roughly equivalent to 67 ft?

2) What is the impact of altitude on Nitrox planning? The text we used didn't address it, but we want to dive a couple of lakes this summer (3000-5000 ft) and would like some reference for planning.

Thanks.

 

[chrpai]

It is generally accepted that Nitrox does not reduce narcosis due to the supsected narcotic effect of Oxygen. You might want to do a search on "Equivilant Narcotic Depth" ( END ) for some previous discussions on the subject.

 

[medical1]

Try this - a buddy wrote it and posted it on his site.

http://www.schmidt.as/NitroxPlan.htm

 

[DeepScuba]

UWS:

DO you know the controversy you just started

2 schools of thought.

1.) Oxygen isn't narcotic so EAD67 is 67ft of narcosis as well.

2.) Oxygen IS narcotic, so EAD of 67ft is still (your example) 90ft of narcosis.

What do I think?

Hell I don't know. I'm on the fence as I don't think it has been answered definitively yet. (Well to some it has, but I ain't touching that one!!!)

 

[chrpai]

Believe it or not I'll air on the side of DIR on this one and say that O2 is narcotic.

For me its a non issue because I don't experience narcosis in the 60-100' range that I prefer to dive in. I dive Nitrox for the added bottom time with no expectation of reduced narcosis.

 

[medical1]

UWS:

DO you know the controversy you just started

2 schools of thought.

1.) Oxygen isn't narcotic so EAD67 is 67ft of narcosis as well.

2.) Oxygen IS narcotic, so EAD of 67ft is still (your example) 90ft of narcosis.

What do I think?

Hell I don't know. I'm on the fence as I don't think it has been answered definitively yet. (Well to some it has, but I ain't touching that one!!!)

I'll take a buzz over a hit! :laser_sho:

 

[Genesis]

I personally do not believe O2 is narcotic.

Yeah, I know GUE thinks it is. But that would certainly be a clear violation of the lipid solubility theory. Of course that theory is typically used to predict anaesthetic properties of various gasses - not exactly what we're dealing with here.... well, ok, I hope not anyway!

In my personal experience a dive to 110' on AIR produces more (subjective) impairment than the same dive on 32%, right up against the MOD. Neither is debilitating (to me.) Indeed, 140' on Nitrox (26% typically) is "ok" from my perspective - but I know that I'm "buzzed".

Determining objective impairment is difficult at the depths at which Nitrox is diveable; as you go deep enough to get really narced, the swing between air and a permissible Nitrox mix (for tox avoidance reasons) becomes finer, and thus, the ability to differentiate becomes difficult.

The problem with claims of narcotic equivalents for metabolically-active gasses (this includes both Oxygen and CO2, which is converted to Carbonic Acid in the bloodstream) is that they fly in the face of the science to date on the matter.

The only "good news" is that the swing between Nitrox and air at depths where narcosis is likely to become a factor for virtually all divers (beyond 100' in depth) is small enough that the absolute answer on this isn't very material. When Narcosis becomes a real issue, in the 130-150' range, you're to the point that all you can really do is replace some of the nitrogen with something else - Helium, for instance.

 

[DepartureDiver]

I believe that oxygen is narcotic and I believe it has been shown to induce narcosis in mice ... granted it is at "higher" pressures. While there have been posts to treat oxygen as either not narcotic or as fully narcotic, there is actually a compromise approach. It would seem that only "free oxygen" (that dissolved in plasma and not bound to a red blood cell) could contribute to narcosis. In general, the vast majority of oxygen is bound to a red blood cell at ppO's of 1.2 to 1.3. Once the ppO's start getting higher, the proportion of oxygen in the plasma starts increasing. Therefore when diving at higher ppO's, oxygen could very well contribute to narcosis and it could be more narcotic than nitrogen. So you can come up with some different fudge factors here, such as treating oxygen as narcotic when diving at ppO's greater than 1.2, or treat the full ppO as half the narcosis of nitrogen, or take the difference between the ppO of your gas at the bottom (i.e. 1.4) and 1.2 and treat the difference as double narcotic such as a .4 increase in the ppN in this example. These are just some off the cuff examples of how to not completely discount oxygen as a narcotic. Of course, the simpliest way would be to just treat the whole exposure as narcotic.

 

[DepartureDiver]

What is the impact of altitude on Nitrox planning? The text we used didn't address it, but we want to dive a couple of lakes this summer (3000-5000 ft) and would like some reference for planning.

Sorry, I missed this part. Narcosis is pressure dependent and is based upon your actual (not altitude theoretical) depth. At altitude, since you are starting at less pressure, your ppN2 will be less for the same sea level depth and the same oxygen percent. While your altitude corrections will decrease you allowable time at depth, you can also use the less pressure to increase your oxygen percentage to get some back. For example, a 90' dive in the ocean on 35% will give you a ppO2 of 1.31 and a ppN2 of 2.43. But if you did a 90' actual depth dive at 5000' (approximate pressure 12.21 psi), on 35%, your ppO2 is now 1.25 and your ppN2 is 2.32. You could increase your oxygen to 37% and get the same ppO2 as the sea level dive and even further reduce your ppN2 (ppO2 1.32 and ppN2 2.24).

 

[UWSojourner]

Oops ... didn't mean to start trouble. I'm really just trying to keep myself and daughter safe.

Maybe this is throwing fuel on the fire, but ... I read the DIR-F book and the GUE Fundamentals of Technical Diving. The risks of Nitrox were given much broader explanation in the Tec book. Much of the explanation seemed to indicate that PO2 > 1.4 should be reserved while doing decompression, and that 1.4 should be considered upper limit for rec diving.

Are there documented cases of Oxy Tox for PO2 < 1.4? Just wondering since most of the data presented in the Tec book seems to be gathered from some poor group of guys who volunteered for the "Let's go breathe until we convulse" assignment.