Accelerated decompression on an argon mix?

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Rhone Man

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I was reading Kevin Gurr's book on tec diving last night, and in particular I was reading about "air breaks". The book was stressing that if you take your "air breaks" on a helium rich bottom mix then it doesn't really affect your overall decompression time because by the time you are at your 30' stop, all the helium has already been off-gassed, so you are only concerned about eliminating remaining nitrogen, and a helium rich bottom gas will be exerting a very low partial pressure of nitrogen so you will still be off-gassing efficiently.

This got me thinking: if that is right, then why do the final decompression stop on pure O2 at all? Why not do it on a blend of (say) 75% oxygen and 25% helium? It would be just as efficient at off-gassing nitrogen, but with a lower risk of oxygen toxicity.

Then I extrapolated the thought some more: helium is expensive, but why could you not use another gas for your 25% filler, such as argon? There would never be any dissolved argon in your tissues, so the same logic would apply - you would be breathing a ppN2 of 0.0 and a ppHe of 0.0 - you are off-gassing as efficiently as you possibly can, but with a much reduced oxygen toxicity risk. And argon is dirt cheap. The knock on argon has always been that it is highly narcotic, but if you were breathing a 25% argon mix at 30 feet, then you still only have an equivalent narcotic depth of 45 feet.

If you wanted to push the envelope, you could even make up a mix of 60% oxygen, 40% argon and start breathing a maximum efficiency off-gassing mix at about 50 feet, and your equivalent narcotic depth is still only around 90 feet.

I can't be the first person to have thought of off-gassing with other gases not already dissolved in the tissues. So does anyone know why this isn't this done?
 
See this: Exotic diving gases for your answer. In summary:
Argon is very narcotic gas (much more narcotic than nitrogen) and also very dense gas leading to breathing difficulties on very deep dives, but it does not cause the distortion of voice like helium or hydrogen does. In theory argon could be used as an decompression gas on shallow depths together with oxygen (argon + oxygen = "argox", argon+O2+N2 = "argonox") to reduce the inert gas absorbance into tissues on ~ 9-15 m decompression stops. Argox/argonox is not suitable for deeper dives due to the high narcotic effects.

Argox is still very rarely used and tested gas for breathing gas' inert component, and argon is mostly used pure as a dry suit inflation gas because of it's good thermal characteristics and relatively cheap price.
 
I won't even pretend to say that I know much about decompression science...

Two issues that do come to mind...

1) I know that the oxygen in my cylinders is appropriate for breathing (aviator/medical grade), and the air that is pumped in them has undergone quality testing, but I have no idea if compressed argon is subject to any testing as far as purity standards. I'd hate for the level of contaminants to be high enough as to present a problem (such as hydrocarbons/carbon monoxide can be an issue if inhaled at high partial pressures). One would have to do a bit of research on what the purity standards are for compressed argon.

2) There's no easy way to test for argon, in the same way one can analyze cylinders for oxygen content. You'd have to be exceedingly careful about blending.

My two cents (worth exactly what you paid for it :wink:)
 
argon's incredibly narcotic
 
I was reading Kevin Gurr's book on tec diving last night, and in particular I was reading about "air breaks". The book was stressing that if you take your "air breaks" on a helium rich bottom mix then it doesn't really affect your overall decompression time because by the time you are at your 30' stop, all the helium has already been off-gassed, so you are only concerned about eliminating remaining nitrogen, and a helium rich bottom gas will be exerting a very low partial pressure of nitrogen so you will still be off-gassing efficiently.

This got me thinking: if that is right, then why do the final decompression stop on pure O2 at all? Why not do it on a blend of (say) 75% oxygen and 25% helium? It would be just as efficient at off-gassing nitrogen, but with a lower risk of oxygen toxicity.

Then I extrapolated the thought some more: helium is expensive, but why could you not use another gas for your 25% filler, such as argon? There would never be any dissolved argon in your tissues, so the same logic would apply - you would be breathing a ppN2 of 0.0 and a ppHe of 0.0 - you are off-gassing as efficiently as you possibly can, but with a much reduced oxygen toxicity risk. And argon is dirt cheap. The knock on argon has always been that it is highly narcotic, but if you were breathing a 25% argon mix at 30 feet, then you still only have an equivalent narcotic depth of 45 feet.

If you wanted to push the envelope, you could even make up a mix of 60% oxygen, 40% argon and start breathing a maximum efficiency off-gassing mix at about 50 feet, and your equivalent narcotic depth is still only around 90 feet.

I can't be the first person to have thought of off-gassing with other gases not already dissolved in the tissues. So does anyone know why this isn't this done?

we know that the best gas differential is a vacuum relative to a partial pressure. 100% o2 has zero inert gas and creates a vacuum to drive gas out of solution. and the fact that it's metabolized only increases this effect (oxygen window)

even if argon was completely benign (and it's not) what benefit would there be over pure o2? the reasoning for trying this seems to be the same put forward by the proponents of using 80% o2. OMG I'M GONNA TOX! lol
if you can hold a stop you'll be fine. if you can't you shouldn't be diving with rich decompression gases.
IMO anyway...
 
Plus, 100% o2 is the best treatment for dcs. By having 100% as your final deco gas, you have the treatment for dcs with you no matter what.
 
It's an interesting proposition. Like one of the other posters, I wonder about purity standards for argon, as it generally isn't produced as a breathing gas. I also wonder about the narcosis . . . it would be interesting to make up a 60/40 O2/Argon mix and sit and breathe it at the surface, and see what it felt like.

As you say, you can't be the first person to have thought of this, which makes me think there is some reason why it doesn't work. But maybe not -- maybe it got naysayed without testing, using the objections already raised. Although I can hold a 20 foot stop without difficulties, I see no reason to object to a strategy that still maximizes offgassing efficiency, and lowers total body and central nervous system oxygen exposure.
 
Argon can easily be made to as high or higher standards than USP He and O2. Most of us aren't breathing "medical" He anyway, USP is actually a pretty poor grade compared to 5 nines industrial or UHP. Although for all practical purposes gas grade is just proportional to the paper trail anyway.

Argon is wicked soluble in addition to being narcotic as all getup. If you breath it any deeper than 20ft you will of course offgas the N2 but will latter need to eventually offgas the argon.
 
100% o2 is the best treatment for dcs
Well, is it -- and if so, Why is it? My understanding that the issue is that 100% O2 is good because it has no N2 or He -- well neither would the Ar mix. As long as there is no N2 or He you have maximized the gradient -- at least that is my understanding.

RhoneMan -- Interesting question and one that begs for thoughtful responses.
 
http://cavediveflorida.com/Rum_House.htm

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