Sorry to pop your bubble, Spike. But "less soluble" does not mean "negligible". See for instance
http://www.dciem.dnd.ca/DCIEM/research/facts/more/dive-tables.html
You can get the bends on oxy-helium; it's just harder.
IIRC, Argon and Xenon have already been experimented with by the military (Navy, I assume); I have heard rumors that
Sulfur Hexafluoride has been experimented with, as well; the molecule is so big it is alleged to not penetrate tissues
fast. I don't know how high they've taken the pressures.
I'm researching the high pressure noble gas toxicity issues. There is (also?) an effect called High Pressure Nervous
Syndrome that is at least somewhat documented. Details when I find something that looks adequately authoritative. This
might be hard, since the exotic mix work is/was probably classified.
Spike Jones wrote:
>
> I am endebted to Anders Sandberg for this idea.
>
> The air we breathe consists of about 0.2 atmospheres
> of oxygen and about 0.8 atmospheres nitrogen. Divers
> have shown that helium can be substituted for the nitrogen,
> since the body does not use either substance. Helium
> actually works better for high pressure applications, since it is
> a noble gas, and so does not react with or dissolve in the
> bloodstream like nitrogen will do under sufficient pressure.
> In a diving bell, oxygen can be held at .2 atmospheres and
> helium added with no apparent harm or discomfort to the
> divers.
>
> The noble gas xenon is chemically similar to helium,
> except for being nearly 33 times denser. If a person
> were to be placed in a pressure chamber with oxygen held at
> 0.2 atmospheres, then xenon added until the total pressure came
> up to about 190 atmospheres, the density of the gas mixture
> in the chamber would be about equal to that of water. The
> person would then float. It would simulate weightlessness
> better than being in water, since the xenonaut could breathe the
> medium in which she was floating.
>
> The partial pressure of oxygen would need to be increased
> somewhat to counteract the tendency of the oxygen to
> float to the top, however there is no reason to doubt that
> humans could swim in xenon. The experience would not
> be exactly the same as floating in your living room however,
> for the pitch of the voice varies as the inverse square root
> of the density of the medium. The xenon swimmer's voice
> would be lowered by nearly 4 octaves, causing her to talk
> like Lurch the butler.
>
> It would take no extraordinary engineering of pressure vessels
> to accommodate 190 atmospheres. In fact even a relatively
> thin walled container would do fine, if one could arrange to lower
> it into the sea as the pressure is raised. Alternately, the chamber
> could be placed at the bottom of a mile-deep shaft and water could
> be allowed to flow in as the pressure is raised, then drained
> as the pressure is lowered. Even if the pressure needed to be
> dropped quickly, this should not present a problem, since it has
> been pointed out that the solubility of xenon is negligible. The worst
> possible effect would be the expanding xenon would escape from
> the bodily orifices into which it has been forced during the
> pressurization, perhaps creating embarrassing noises.
>
> The one killer app for weightlessness that eeeeveryone wants
> to try might not work out either, since one likely could not
> breathe fast enough. The dense column of xenon would resist
> changing direction quickly, so the participants could scarcely
> get their breathing rate much above 1 Hz, insuffient for this
> kind of activity. Then there's the problem of sounding like
> Jabba the Hut and Mrs. Hut on their honeymoon, which might
> in itself spoil the mood. Other than that, one could put together
> a really cool sensory deprivation chamber. spike
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