Accelerated decompression on an argon mix?

[Cave Diver]

Interesting . . . the results of the space study certainly raise a suspicion in my mind that solubility may be more important than anything else. One of O2's qualities is that it is really very poorly soluble, and this is true of He as well. Hmm.

Are you referring to the lipid solubility and the links made between that and narcotic effects of a gas? (I haven't read the article yet)

 

[Blackwood]

Are you referring to the lipid solubility and the links made between that and narcotic effects of a gas? (I haven't read the article yet)

I believe she's talking about how solubility plays into gas loading as it relates to decompression, not narcosis.

 

[fppf]

I think the main property of a gas that makes it "good" or "bad" is how stable it is at supersaturation (solubility).

In the decompression models they call this the "M" values, or the pressure gradient that is allowed for a gas and a tissue where it wont come out of solution.

Argon maybe really slow to on gas and off gas. But if it comes out of solution with very low pressure gradients it will make a bad breathing gas.

Just my opinion, I don't have any facts behind that, your mileage may vary.

 

[rjack321]

I can't point to it now, but I do remember reading some tests where they bent patients on pure oxygen.

For EVAs in space this is plausible and has been done. Its not an issue no matter how long your scuba deco though.

 

[DA Aquamaster]

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.

This could catch on as a recreational drug.

I can envision people going around with little argon double sets like Steve Martin as the Dentist in "Little Shop of Horrors" with his NO2 doubles.

For EVAs in space this is plausible and has been done. Its not an issue no matter how long your scuba deco though.

Pilots in high altittude aircraft like the U2/TR-1, SR-71 and WB-57 also pre-breath 100% O2 prior to flight to reduce the potential for a DCS hit at high altitudes in the event of low cabin pressure differentials and cabin pressurization system failures. Pressure suits are worn, but they are also low pressure suits, as higher pressures greatly reduce mobility in a soft suit.

The same procedures were followed in projects Mercury, Gemini and Apollo as well as the Apollo/Soyuz and Skylab programs as the space craft used a reduced cabin pressure with 100% O2.

So...when you talk about bending someone on 100% O2, what needs to also be discussed is the precipitating event - the decompression from their normal 1 ATA environment where their tissues were already saturated with nitrogen for that pressure.

 

[Rhone Man]

Anyway, here is an article for research in space sciences. Most people don't know, but astronauts need to decompress from the shuttle atmosphere to make an EVA. The space suits only have about 4.5 PSIA of internal pressure while the shuttle is held at 14.7 PSIA or normal atmosphere. The procedures followed use oxygen currently. This study looked at using an Argon oxygen mix for there decompression to 3.5 PSIA for mars missions. They found a significant increase in DCS incidence when argon was used over pure oxygen.

Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures

I suspect that is the answer, although I note in the study they were looking at 38% oxygen, 62% argon; whereas I was contemplating something more in the line of 75% oxygen, 25% argon. No matter how rapidly argon dissolves into the body, I can't see a risk of getting bent on a 25% argon mix at 20 (or 30) feet.

The point about argon not having been purified for breathing is also well taken. Similarly I hadn't contemplated the denser gas being harder to breathe, although again, probably not really an issue with only a 25% argon content.

 

[texdiveguy]

The average cost for Argon is a bit over $1cf..

 

[fppf]

Some comments about argon in general.

Argon is pulled out of the air. So the cost is not that high, and it does not leave the planet like helium does. I don't have quotes that are current because I don't go through that much welding. But prices for argon vary by area and supplier but you can get a 300 CF cylinder for anywhere from $50 to $80. No where near what a dive shop charges people. Can you see how much money there making?? If your paying $1 per CF I would shop around.

As for purity, you can get argon in any purity you want. Industrial grade argon used for welding is pretty pure. You need to check the specs at your gas supplier but the purity is driven by the welders. Having impure gas will cause bad welds and cost big bucks $$$. Remember its fractional distilled from air, that process alone makes very pure gases.

 

[ianr33]

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,

I have a hard time believing that.

If it is true then you could use heliox (helium and oxygen) as a bottom mix with 50% nitrox and o2 for deco. If all the helium has gone by 30 feet,and the only nitrogen you have ongassed is from 70 feet up then deco would be almost nothing.
Sounds too much like a free lunch to me!

 

[Rhone Man]

I have a hard time believing that.

If it is true then you could use heliox (helium and oxygen) as a bottom mix with 50% nitrox and o2 for deco. If all the helium has gone by 30 feet,and the only nitrogen you have ongassed is from 70 feet up then deco would be almost nothing.
Sounds too much like a free lunch to me!

I am not a trimix diver - I am just quoting the man (see page 141).