Nitrox Not Helping With Narcosis... It's not making sense.

[gcarter]

If helium were convenient and cheap, it still wouldn't make a great supplement for extending NDLs on dives not subject to narcotic partial pressures of nitrogen.

What about for the range say 90' - 130'?

I know, I know, I should do some reading on trimix first. But if cost were not an issue, is there any reason why helium should not be more widely used at those recreational depths?

 

[Hetland]

What about for the range say 90' - 130'?

I know, I know, I should do some reading on trimix first. But if cost were not an issue, is there any reason why helium should not be more widely used at those recreational depths?

I'm certainly not an expert, but here's my limited understanding on the subject:

Helium is an inert gas, and it loads into your tissues just like nitrogen. It won't "block" nitrogen from loading into your tissues, but it could reduce the partial pressure of nitrogen, which would affect loading and offgassing. However now you're loading helium too, and if your ascent rate is too fast, you'll get helium bends. Since it's a "faster", lighter gas, helium, at the same partial pressure will super-saturate your tissues faster than an equivalent pp of nitrogen (though it offgasses faster too).

So you're going from two problematic gasses in your mix, to three.

Helium isn't used to extend NDL's, it's used to mitigate narcosis. It might change the math some, but at the cost of further complication. Some folks advocate helium mixes for anything deeper than 80ft. If cost were not an issue, I'd find that hard to argue against, but it shouldn't be done without an understanding of the trade you're making.

If you're worried about NDL's at recreational depths, dive an appropriate nitrox mix.

 

[gcarter]

I'm certainly not an expert, but here's my limited understanding on the subject:

Helium is an inert gas, and it loads into your tissues just like nitrogen. It won't "block" nitrogen from loading into your tissues, but it could reduce the partial pressure of nitrogen, which would affect loading and offgassing. However now you're loading helium too, and if your ascent rate is too fast, you'll get helium bends. Since it's a "faster", lighter gas, helium, at the same partial pressure will super-saturate your tissues faster than an equivalent pp of nitrogen (though it offgasses faster too).

So you're going from two problematic gasses in your mix, to three.

Helium isn't used to extend NDL's, it's used to mitigate narcosis. It might change the math some, but at the cost of further complication. Some folks advocate helium mixes for anything deeper than 80ft. If cost were not an issue, I'd find that hard to argue against, but it shouldn't be done without an understanding of the trade you're making.

If you're worried about NDL's at recreational depths, dive an appropriate nitrox mix.

LOL, if you saw my SAC you would know that NDLs are most certainly not an issue for me (although I do use Nitrox). Just curiosity. Thanks for the answer.

 

[ajduplessis]

I'm certainly not an expert, but here's my limited understanding on the subject:

Helium is an inert gas, and it loads into your tissues just like nitrogen. It won't "block" nitrogen from loading into your tissues, but it could reduce the partial pressure of nitrogen, which would affect loading and offgassing. However now you're loading helium too, and if your ascent rate is too fast, you'll get helium bends. Since it's a "faster", lighter gas, helium, at the same partial pressure will super-saturate your tissues faster than an equivalent pp of nitrogen (though it offgasses faster too).

So you're going from two problematic gasses in your mix, to three.

Helium isn't used to extend NDL's, it's used to mitigate narcosis. It might change the math some, but at the cost of further complication. Some folks advocate helium mixes for anything deeper than 80ft. If cost were not an issue, I'd find that hard to argue against, but it shouldn't be done without an understanding of the trade you're making.

If you're worried about NDL's at recreational depths, dive an appropriate nitrox mix.

Correction: Helium does not load faster than N2!! It does however off-gass faster than N2.

 

[Searcaigh]

Ne, what's that then Neon?

 

[Crowley]

And around and around and around we go....

Firstly I think it's important to remember that "Nitrogen Narcosis" is something of a misleading or out-dated term. For recreational diving, the gas we breathe is comprised mostly of nitrogen, whether that's air or 32/36 whatever percent nitrox.

The second thing is that whilst we all know that Nitrogen is the "bad gas" when it comes to decompression sickness, including the formation of microbubbles and so on, there is no correlation between the bends and narcosis - they are two completely different physiological phenomena, apart from the fact that they are both related to the absorption of gas under pressure.

In my limited medical understanding, narcosis is to do with the absorption of gas into the nerve cells which interferes with the transmission of electrical signals from the nerves across the chemical connection between them, axons and dendrons and whatnot, in the same way that this chemical reaction is interfered with through consumption of alcohol and/or recreational drugs. This is based on the solubility of the particular gas in the proteins which constitute our nervous systems. I was told that this is possibly due to the molecular weight of the gas involved, which seems to be roughly on the right track if you have a copy of the periodic table and a calculator to hand - Oxygen weighs slightly more than nitrogen, and much less than carbon dioxide or argon, so theories that oxygen might be more narcotic than nitrogen would bear out in that example, should it prove accurate.

It doesn't matter that oxygen is metabolised by the body or not, this goes back to decompression sickness, not narcosis, it's more a function of the gas being stuck somewhere it's not supposed to be, rather than whether or not it's useful to the human body or not. If I put petrol into my car's fuel tank, it will make it go, but if I stick it in the oil reservoir, it will have a much different effect.

As to whether or not oxygen can be proved to be narcotic or not underwater, I would suggest that it's an experiment that is impossible to undertake. Pure oxygen will cause you to have convulsions before you even reach a depth at which it becomes narcotic, and even if that could be suppressed by the application of anti-convulsants, the physiological effect of those drugs would be almost impossible to measure.

What we do know - from everyday diving, is that whether or not you dive on air or recreational nitrox, you will get narced at depth. I've seen it happen as shallow as 25 metres, and I feel it myself if I pass 30, which I do rarely. Helium is proven to be much less narcotic, and is therefore used by deeper technical divers to reduce the narcotic effect of the gas being breathed, unless you descend past 200 metres, when it causes HPNS (High Pressure Nervous Syndrome), but there are very few divers that ever go there, and those that do, sadly, don't always come back due to the effects of the other gases that are being absorbed into the body - primarily carbon dioxide at that depth.

Like decompression sickness, research into the phenomenon of narcosis has its limitations, because the only way to start proving things accurately would be to subject human beings to conditions that might cause them irreparable damage or death, and whilst diving is a popular sport, most funding bodies are concerned with giving money to organisations that study conditions that affect the entire human race - such as cancer - not recreational divers.

What I can tell you, as can most of my colleagues, quite categorically, is that - at least in terms of recreational diving - the difference between diving with air or nitrox is, in terms of susceptibility to narcosis - miniscule.

Cheers,

C.

 

[ajduplessis]

Ne, what's that then Neon?

Correct

 

[Hetland]

Correction: Helium does not load faster than Ne!! It does however off-gass faster than N2.

I'm not sure that's true. I understood that helium does load faster. Any perceived equality between the two could be chalked up our being saturated with a 79% nitrogen mix at one atmosphere. As we descend, we add a higher pp of helium, and a lower (hopefully) pp of nitrogen, but we're starting out with more nitrogen in the blood before we ever hit the water. As a result, there is an initial "faster" load of nitrogen that's quickly outpaced by the helium load rate.

I'm not trying to start an argument. My knowledge on the subject is incomplete at best. If I 'm incorrect, I hope to be corrected.

 

[Searcaigh]

Correct

I am confused then, where does Neon come into the equation, perhaps I missed a post, but I don't recall it being used as a diving gas

 

[Hetland]

I am confused then, where does Neon come into the equation, perhaps I missed a post, but I don't recall it being used as a diving gas

iirc, neon is less narcotic than helium, but many, many times more expensive. don't quote me on that though. most, if not all of the inert trace gasses have been tried as diving gasses, including hydrogen. I'm not confident that I'm correct on neon though, I may be mixing it up with xenon.

I'm guessing ajduplessis just mistyped.