DIR- Generic Why use GUE nitrox only

[boulderjohn]

I really can't believe what I am reading about the possibility that oxygen might be narcotic. It used to be taken as gospel that oxygen was at least as narcotic as nitrogen, and possibly more so. GUE absolutely taught that. The problem always was that it was difficult to test without saturating subjects to the point of toxicity. It was believed to be narcotic because according to the Meyer-Overton hypothesis for the cause of
narcosis, oxygen should be more narcotic than nitrogen--but the result depended upon the degree to which it was metabolized.

It was only a couple years ago that new studies suggested that gas mixtures with higher oxygen levels (nitrox) might be somewhat less narcotic than air.

 

[grf88]

I really can't believe what I am reading about the possibility that oxygen might be narcotic. It used to be taken as gospel that oxygen was at least as narcotic as nitrogen, and possibly more so. GUE absolutely taught that. The problem always was that it was difficult to test without saturating subjects to the point of toxicity. It was believed to be narcotic because according to the Meyer-Overton hypothesis for the cause of
narcosis, oxygen should be more narcotic than nitrogen--but the result depended upon the degree to which it was metabolized.

It was only a couple years ago that new studies suggested that gas mixtures with higher oxygen levels (nitrox) might be somewhat less narcotic than air.

It appears to have come full circle.

 

[justinthedeeps]

I really can't believe what I am reading about the possibility that oxygen might be narcotic. It used to be taken as gospel that oxygen was at least as narcotic as nitrogen, and possibly more so. GUE absolutely taught that. The problem always was that it was difficult to test without saturating subjects to the point of toxicity. It was believed to be narcotic because according to the Meyer-Overton hypothesis for the cause of
narcosis, oxygen should be more narcotic than nitrogen--but the result depended upon the degree to which it was metabolized.

It was only a couple years ago that new studies suggested that gas mixtures with higher oxygen levels (nitrox) might be somewhat less narcotic than air.

Yeah I deeply respect careful curriculums, and initially believe both PADI and GUE on the oxygen narcotic thing. Stay safe and smart, right? It can't hurt. Especially if we're in who's knows where, breathing who knows "oxygen," or nitrox with twice the argon, CO2, and CO that air does (thank u, membrane concentrators...)

Unless puting in more helium to reduce "oxygen narcosis" is also bad.
But we're not actually sure whether that is true, either.....

No problems with keeping the "oxygen narcotic" in your gas planning. Conservatism still wins there probably.

 

[inquis]

Are you considering oxygen to be narcotic?
Subsurface doesn't agree with your numbers either, unless you check the "oxygen is narcotic" box--which I think is a myth, unless your oxygen isn't actually pure oxygen (argon impurities being the biggest culprit)

I considered the possibility you might have used nitrogen-only END, but considering oxygen+nitrogen to be narcotic was the closest answer to yours. At 57 m (187 ft), 21/35 has a PO2 of 1.4, a traditional END (O2+N2 narcotic) of 33.5 m (110 ft), and a nitrogen-only END of 19 m (64 ft). EDIT: I got this wrong. It is 27m.

END = (Depth + W) F_narc - W
where W is either 10 m or 33 ft to match the depth units and F_narc is the narcotic fraction: 1-FHe for traditional END, EDIT: (1-(FHe+FO2))/0.79 for nitrogen-only END.

 

[harvalen]

END = (Depth + W) F_narc - W
where W is either 10 m or 33 ft to match the depth units and F_narc is the narcotic fraction: 1-FHe for traditional END, 1-(FHe+FO2) for nitrogen-only END.

I think you want to divide the F_narc by .79 for nitrogen-only END. Otherwise you would end up with the END of AIR at 40 m being: (40+10) (1-.21) - 10 = 29.5 m

In that case you end up with: (57+19)(1-(.35+.21))/.79 - 10 = 27.3

 

[justinthedeeps]

END = (Depth + W) F_narc - W
where W is either 10 m or 33 ft to match the depth units and F_narc is the narcotic fraction: 1-FHe for traditional END, 1-(FHe+FO2) for nitrogen-only END.

Ok here is a verbal story problem format for the math I am going by:

Start with the partial pressure of the gas that you consider narcotic. This is how it affects us.

The ppN₂ on air at 30 metres is 4atm * 0.79, or 3.16atm of N₂.

At 20 metres on air, the ppN₂ is 3atm * 0.79, or 2.37atm of nitrogen.

Now consider what is the ppN₂ of your 21/35. The nitrogen fraction of this is 0.44 (1-0.35-0.21).

At 57 metres, the ppN₂ is 6.7atm * 0.44, or about 2.9 atmospheres. This is above the air equivalent at 20 metres, but below the air equivalent at 30 metres. This should quickly make sense, because the nitrogen has been reduced by almost half, and we are now almost twice as deep.

In fact, it equates to air at about 27 metres, because 2.9atm / 0.79 = 3.7 atm, or ~27 metres.

For an END of ~20m, just divide 2.37atm by the fraction of nitrogen in your mix, i.e. 0.44. 2.37atm / 0.44 is 5.4atm, or about 44 metres for 21/35 to have as much nitrogen pressure as air at 20 metres.

I'm not going to bother typesetting out more equations here, but they are not that bad. Easily derived by directly considering nitrogen partial pressures.

I can't take credit for this myself, in fact it has been included in courses and gas planning discussions from experienced Mod3 rebreather instructors.

 

[TravisD]

The price of oxygen is ridiculously variable. The first time I opened an account, I was charged $90 for a 300 cubic foot bottle. I immediately protested that I knew someone getting it for $60. The guy said, "OK, I can do that." As time went on and I became a regular customer, the same bottle would cost me about $20--from the same company.

I paid $80 for a T of ABO a couple months ago, my first time buying O2 for my new-to-me compressor/stick setup. Probably go Welding grade next time I need to bank Nitrox - I don't use a lot of it though at this point.

 

[inquis]

I think you want to divide the F_narc by .79 for nitrogen-only END.

Yes, thanks for that correction. I normally use the traditional version for conservatism, so the N2-only version isn't as ingrained. That gives the ~27m figure that @justinthedeeps gave. Sorry for the confusion.

 

[justinthedeeps]

@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.

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

Take it up to 2.0atm in a deco chamber. These patients aren't narced by it either.

What is the actual evidence that oxygen is narcotic?

Are we "disagreeing," but without any evidence?

 

[Alekseolsen]

@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.

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

Take it up to 2.0atm in a deco chamber. These patients aren't narced by it either.

What is the actual evidence that oxygen is narcotic?

Are we "disagreeing," but without any evidence?

I guess the point is you also wouldn't find anyone beeing narced by breathing 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.


Edit: the usual typos