OP
Perhaps it would be interesting to look at the ascent rates for different gases as they are being taught by the various technical agencies. Can you shed any light on this?
Helium the Perfect Diver's Gas
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Perhaps it would be interesting to look at the ascent rates for different gases as they are being taught by the various technical agencies. Can you shed any light on this?
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"Helium will bend you more than nitrogen" from a fast ascent is a bit of a myth.
Rubicon Research Repository: Item 123456789/6582
and
http://archive.rubicon-foundation.org/6496
even under rapid "explosive" (5 second) decompression from >200ft trimix diving guinea pigs had 1.6x more nitrogen in their arterial blood gases. I wish I knew the mixes being dove, but the bottom line is that helium isn't very soluble so there's not as many moles to offgas. Fewer moles of gas in smaller bubbles to begin with = lower DCS risk not more.
Rubicon Research Repository: Item 123456789/6582
and
http://archive.rubicon-foundation.org/6496
even under rapid "explosive" (5 second) decompression from >200ft trimix diving guinea pigs had 1.6x more nitrogen in their arterial blood gases. I wish I knew the mixes being dove, but the bottom line is that helium isn't very soluble so there's not as many moles to offgas. Fewer moles of gas in smaller bubbles to begin with = lower DCS risk not more.
OP
That's my understanding as well, but obviously there are those that believe this to be a problem. It's correct that Helium is diffused at a faster rate; it's solubility is something like 40% less (the exact figure eludes me at the moment) than Nitrogen.
I'm interested in what the technical organizations are teaching for ascent rates. All rates given by the certification agencies for air are to fast, as far as I'm concerned. I'm biased by my military and commercial background here and don't have the "technical agency answers."
This looks like a more complete report on this series of experiments
Rubicon Research Repository: Item 123456789/2613
Rubicon Research Repository: Item 123456789/2613
Cost is an issue.
But I also think liability is likely to be a severe retardant on Helium mixes going mainstream. Anyone remember the fuss over Nitrox?
But I also think liability is likely to be a severe retardant on Helium mixes going mainstream. Anyone remember the fuss over Nitrox?
The liability could be an issue. I recall one shop that made me wait until the cylinder cooled to room temperature and then sit there for 5 minutes as their O2 meter "stabilized" for the confirmation of the mix. I'd hate to think what they would do if it there was He in the mix.
Right.
Andrew Georgitis tells a tale of diving with a guy who did all the mixing for the group. If you have ever done a whole lot of tanks using helitrox or trimix, you know that things can get a little confusing if you are not paying strict attention. You have a whole bunch of tanks at different stages of the blending process, and you are often moving from one source tank to another repeatedly. In this case, when filling his own doubles, the blender added O2 instead of He at that point in the process, resulting in a double dose of O2 in the mix. He then failed to test the O2 levels.
He did manage to survive his bout with CNS toxicity, but it was very close to not being true--miraculous, IMO.
OP
Why do you think this Rhone man? Helium has a long diving history. If the purpose is to eliminate narcosis and decrease the incidence of DCS, how would this be seen legally as an unreasonable standard of care?
The dive industry is just super super cautious about new things. Nitrox was the voodoo gas for years. DEMA effectively tried to ban it in 1991 without any scientific basis. Still no agency will let kids use, again for no sane given reason. Giving helium mixes to the great unwashed masses... I just suspect they would freak.
OP
Ah the politics of recreational diving. Don't look at the medical benefits or the science. Ban things that we don't understand.
Excellent point. This leads into the part of my question about the misconceptions of Helium, which seems to be an obstacle to wider use.
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