Posted by Karl S. on July 09, 2003 at 09:01:05:
In Reply to: Re: Xeno gas posted by Bill Reals on July 08, 2003 at 15:00:59:
50-50 HeliAir, which is the equivalent of 11/50 Trimix, works to 260 fsw and is most applicable for an MOD range of 240 to 260 fsw.
For less than 240 fsw I would use 45% helium and 55% air as a HeliAir mix.
For deeper than 260 fsw I would use more helium in the mix and less air.
The main benefit of HeliAir, besides being easy to mix, and easy to test with just an oxygen analyzer, is that it contains lower partial pressures of oxygen than conventional trimixes do. That makes it "safer" than conventional trimixes.
Trimixes are more akin to helium blends of EANx, and you have all the oxygen toxicity considerations with them than you do with HeliAir.
HeliAir has however a higher content of "inert gas" in terms of helium and nitrogen, therefore slightly longer deco times can be expected than with more oxygen rich trimixes. THAT is the only difference between HeliAir mixes and other more conventional trimixes.
The next threshhold of gas mixes is HeliOx.
What do you put in your tanks? That is always question #One. For example: HeliAir, Trimix, or HeliOx? And what is the difference? Those are the initial questions every diver needs to ask, depending on the conditions expected during the dive.
Other than dogma and repeated B/S, no one has effectively given any intelligent reason not to mix HeliAir, and that is why it is still fairly popular today.
The future of mixed gas diving probably lies in the realm of Neon replacing Helium. But with Neon's high cost, that is still way in the future. The good news is that we will never run out of Neon, since it is a natural component of the atmosphere, like argon. The bad news is that it is a really low component, which makes it expensive and more work to distill it out of the air.
Post a Followup