DIR- Generic Why use GUE nitrox only

[Nick_Radov]

@Nick_Radov I see you "disagree" with me saying that pure oxygen isn't narcotic.

Do you have reasons or evidence that oxygen is narcotic?

Anyone?

There are a very large number of data points now to show that people breathing good pure 100% oxygen at 6 metres, a ppO2 of 1.6atm--the maximum--are not narced at all. That includes both open circuit and rebreather divers. This also includes military divers on oxygen-only rebreathers.

Regardless of whether oxygen is narcotic or not, the narcotic effects of oxygen and/or nitrogen mixes are negligible at 20ft / 6m. So, I don't understand what point you're trying to make. How does this even matter for real-world diving?

If oxygen is less narcotic than nitrogen (and the research so far isn't really conclusive on way or the other) then there could be a tiny reduction in total narcotic effect from breathing 32% instead of 21% at 100ft / 30m. But again, this is mostly irrelevant for real-world diving because the more significant risk is from hypercapnia: carbon dioxide is far more narcotic than oxygen or nitrogen, and CO2 causes a variety of other deleterious neurological effects. Hence the importance of keeping gas density within reasonable limits.

 

[justinthedeeps]

I guess the point is you also wouldn't find anyone beeing narced by vreathing air at those depth, this nitrogen aint narcotic?

Due to tox limits its not possible to measure narcotic when breathing pure O2, but that doesn't necessarily mean that O2 won't contribute to the narcotic effect as part of the breathing mix.

A test would be to try breathing air at 40 meters, and then swap to some Odd 10/11 trimix mix. Would ofc be horrible for deco/NDL purposes, but you'd keep the same amount of N2, halving O2, so if there is a narcotic effect it should be measurable.

Yeah I agree, it gets really weird trying to think up some kind of odd scenario in which pure oxygen itself somehow might be narcotic... if only we could get it up to 3 atm or whatever... at 40 metres... it's just a huge stretch with unrealistic or impossible mixes, with not much evidence to back it up.

Unless your oxygen came from a membrane or pressure swing system that concentrates other narcotic gases alongside oxygen?

I think modern field evidence points to that pure oxygen is basically not narcotic enough to matter in END calculations, or if it is, it will kill you from CNS convulsions before that (2+ atm)

 

[justinthedeeps]

Regardless of whether oxygen is narcotic or not, the narcotic effects of oxygen and/or nitrogen mixes are negligible at 20ft / 6m. So, I don't understand what point you're trying to make. How does this even matter for real-world diving?

If oxygen is less narcotic than nitrogen (and the research so far isn't really conclusive on way or the other) then there could be a tiny reduction in total narcotic effect from breathing 32% instead of 21% at 100ft / 30m. But again, this is mostly irrelevant for real-world diving because the more significant risk is from hypercapnia: carbon dioxide is far more narcotic than oxygen or nitrogen, and CO2 causes a variety of other deleterious neurological effects. Hence the importance of keeping gas density within reasonable limits.

I am very happy to agree with you that oxygen narcosis is not our biggest concern.

But I don't think depth is what matters, it is partial pressures that matter. Nitrogen theory is completely based on partial pressures--not depths--and this is completely accepted.

Why should oxygen be any different? A ppO2 of 1.6atm (e.g. 100% at 6m) should have the same effect on us, regardless of depth.

This is also the whole principle by which rebreathers work. It's why we happily do dives at say ~1.3 ppO2, regardless of depth, and the effect of that same partial pressure of oxygen on us is the same whether it is at 10 metres or 100 metres.

 

[justinthedeeps]

Well anyway to try to recover this thread, I think it's great that GUE prefers to use nitrox, the ppN2 reduction is fantastic, and the ppO2 increase is totally justifiable as something that is standing in for an "inert gas." (Within MOD, that is)

But then again, strangely refusing to accept that air is also fine to say ~20 metres is sooo GUE.

 

[Lorenzoid]

Well anyway to try to recover this thread ….

But then again, strangely refusing to accept that air is also fine to say ~20 metres is sooo GUE.

And further in the spirit of recovering this thread, the OP said they went to a “GUE shop” and was given a hard time about wanting an air fill. It is GUE’s standard gas for recreational depths, that’s all. The shop probably does receive customers who are not GUE trained and just want air, and the shop is probably okay with that. (The OP did not elaborate, but that’s my guess based on my local shop.)

 

[ginti]

To the OP @johnydive, sorry for your experience, it should not be like that. Yes, nitrox is more optimal than air, almost always (and when it isn't more optimal than air, air is anyway not the best option - trimix is). People explained why, although there is a lot more about gas standardization (mainly related to big exploration projects, something GUE pushes so much).

However, for obvious logistic and cost reasons, many divers with GUE training often use air.

I will tell you what I would do If that schooling was something arrogant and annoying, I would change shop. If it was just a casual chat while waiting for the tanks to be filled, I would take it for a casual chat and forget it.

Why should oxygen be any different? A ppO2 of 1.6atm (e.g. 100% at 6m) should have the same effect on us, regardless of depth.

I honestly do not manage to follow your reasoning, would you explain where I am wrong here?

At 30m (roughly 100ft), and assuming breathing air, the partial pressure of N2 is 0,79*4=3,16 bar, while the O2 one is 0,21*4=0,84 bar. Of course, the sum of the two is 4 bar.

Now there are two possibilities:
- O2 is not narcotic at all: in this case, breathing pure O2 at 6m would not cause any issue by definition; so decompression with pure O2 at 6m without narcotic effects is compatible with this solution.
- O2 and N2 are both narcotic: the pressure responsible for narcosis is the partial pressure of N2+O2, which in the case of both air and pure oxygen is the total pressure. Assuming we start seeing narcotic effects at 30m, the pressure to cause narcosis should be no less than 4 bar. Therefore, of course, with a partial pressure of 1.6, we see no narcotic effect. Decompression at 6m with pure oxygen is therefore compatible with this solution too.

Because decompression at 6m with pure oxygen is compatible with both options, it is irrelevant to demonstrate or negate any O2 narcotic effect. Am I missing something? Would you point out my mistakes, if any?

 

[justinthedeeps]

To the OP @johnydive, sorry for your experience, it should not be like that. Yes, nitrox is more optimal than air, almost always (and when it isn't more optimal than air, air is anyway not the best option - trimix is). People explained why, although there is a lot more about gas standardization (mainly related to big exploration projects, something GUE pushes so much).

However, for obvious logistic and cost reasons, many divers with GUE training often use air.

I will tell you what I would do If that schooling was something arrogant and annoying, I would change shop. If it was just a casual chat while waiting for the tanks to be filled, I would take it for a casual chat and forget it.



I honestly do not manage to follow your reasoning, would you explain where I am wrong here?

At 30m (roughly 100ft), and assuming breathing air, the partial pressure of N2 is 0,79*4=3,16 bar, while the O2 one is 0,21*4=0,84 bar. Of course, the sum of the two is 4 bar.

Now there are two possibilities:
- O2 is not narcotic at all: in this case, breathing pure O2 at 6m would not cause any issue by definition; so decompression with pure O2 at 6m without narcotic effects is compatible with this solution.
- O2 and N2 are both narcotic: the pressure responsible for narcosis is the partial pressure of N2+O2, which in the case of both air and pure oxygen is the total pressure. Assuming we start seeing narcotic effects at 30m, the pressure to cause narcosis should be no less than 4 bar. Therefore, of course, with a partial pressure of 1.6, we see no narcotic effect. Decompression at 6m with pure oxygen is therefore compatible with this solution too.

Because decompression at 6m with pure oxygen is compatible with both options, it is irrelevant to demonstrate or negate any O2 narcotic effect. Am I missing something? Would you point out my mistakes, if any?

This is excellent. Thank you for a counterpoint keeps us thinking! Sounds pretty convincing and compelling.

Is there a testable hypothesis?

The 21/35 seems like a great candidate for considering how much oxygen contributes to narcosis. If oxygen is not narcotic, then by ppN₂ alone, it shouldn't start to get really narcy until about 50 metres. If you do believe the oxygen is narcotic, then it gets narcy before 40 metres. The latter sounds a bit weird to me, 21/35 narcosis as shallow as 35 metres?

We could take a poll and probably get votes on each side, based on experience. YMMV...?

BUT I am also curious how that 21/35 was made. Was it partial pressure blended from pure sources, including ABO or better pure oxygen? Or was EAN32 pumped on top of some helium? How was that EAN32 made? Some membrane and pressure swing systems concentrate argon and CO2, both very narcotic gases themselves.

 

[ginti]

This is excellent. Thank you for a counterpoint keeps us thinking! Sounds pretty convincing and compelling.

Actually, I am not trying to convince anybody here - I do not have enough knowledge and not enough time to set up rigorous experiments.

My point was only about understanding your reasoning, nothing more, nothing else

 

[boulderjohn]

Do you have reasons or evidence that oxygen is narcotic?

It goes to the Meyer Overton hypothesis on anesthesia. If you do a Google search, you will find it thoroughly explained in detail on many sites. There are entire books written on it.

Here is a recent study showing that nitrox might have some benefit over air in terms of narcosis, suggesting that the previous belief that oxygen was just as narcotic as nitrogen might be exaggerating the effect. Here is the post from Dr. Simon Mitchell in which he introduces the study and in which he says the following:

On balance, I favour the argument that oxygen is less narcotic at the pressures we can safely breathe because there is a substantial gap between inspired and tissue PO2 due to metabolism in the tissues that matter for a narcotic effect. In contrast, the gap between inspired and tissue tensions of nitrogen in the brain is almost zero because the brain is a very fast tissue. Having said that the functional difference in narcotic effect is probably quite small. If we really want to avoid narcosis, then breathing helium is the key.​

I presume that you have in fact breathed 100% oxygen at 6 metres / 20 feet. Were you narced?

OF course not, because the PPO2 is not great enough by itself to create the effect. That does not mean it does not contribute to the total effect when combined with nitrogen. You cannot test to see if pure oxygen is narcotic by itself because getting to the necessary PPO2 will cause oxygen toxicity.

EDIT: I originally forgot to add the link to the study.

 

[justinthedeeps]

It goes to the Meyer Overton hypothesis on anesthesia. If you do a Google search, you will find it thoroughly explained in detail on many sites. There are entire books written on it.

Here is a recent study showing that nitrox might have some benefit over air in terms of narcosis, suggesting that the previous belief that oxygen was just as narcotic as nitrogen might be exaggerating the effect. Here is the post from Dr. Simon Mitchell in which he introduces the study and in which he says the following:

On balance, I favour the argument that oxygen is less narcotic at the pressures we can safely breathe because there is a substantial gap between inspired and tissue PO2 due to metabolism in the tissues that matter for a narcotic effect. In contrast, the gap between inspired and tissue tensions of nitrogen in the brain is almost zero because the brain is a very fast tissue. Having said that the functional difference in narcotic effect is probably quite small. If we really want to avoid narcosis, then breathing helium is the key.​

Great info, thanks for keeping this discussion interesting

OF course not, because the PPO2 is not great enough by itself to create the effect. That does not mean it does not contribute to the total effect when combined with nitrogen. You cannot test to see if pure oxygen is narcotic by itself because getting to the necessary PPO2 will cause oxygen toxicity.

So yes here I think this identifies where uncertainty comes up. Do the effects of ppO2 and ppN2 really just add up like that, to an easily explainable combined effect? A simple arithmetic, but what is the mechanism by which that actually works?

Other gas theory say that gases are operating independently with regard to partial pressure effects. And nitrogen reportedly behaves quite differently in the body versus oxygen.

Alcohol and diving clearly don't mix, for many reasons. I would be very willing to believe that the biological mechanism of alcohol on the brain is similar enough to nitrogen that their narcotic effects are directly additive. Synapses and membranes are being directly disrupted.

Does oxygen do this? What mechanisms are proposed to explain how oxygen results in narcosis? Is VENTID the same as inert gas narcosis? Do they actually just add up? Or is something else going on?

And is 21/35 really narcotic shallower than 50 metres, because of the oxygen in it? Not in my experience, but I honestly haven't experimented with this in enough conditions to say with certainty.