Posted by bbc on August 21, 2001 at 08:32:27:
GI responded to someone also asking about heli-air on another list. Thought it might be of interest.
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"heli air " is a Sheck Exley saying. You make it by putting in only helium and air, and it comes out to about 10/50 - half helium and half air. Depending on pressure, for most mixes you need to add some oxygen. As you try to get higher ppo2,s the helium becomes uselessly minute in the mix.
Keep in mind that Exley was a big proponent of diving narcotic mixes, so any other mix with helium and air tended to be more narcotic. Exley used to say, "It is more natural", one of his bullshit sayings that Gavin and I talked him out of after he dove with us for a while.
You need to apply Rule Number One of diveshops, "Don't listen to anything they say".
-----Original Message-----
From: Paul M. Deniston [mailto:pdeniston@mediaone.net]
Sent: Monday, August 20, 2001 10:16 PM
To: trey@netdor.com
Subject: What's the difference between heli-air and trimix?
Trey:
I was talking w/ a shop owner about some advanced training and he mentioned heli-air. What the hecks the difference between heli-air and trimix other than the fact that heli-air is by definition less than 21% O2? He was discussing using it as a gas that could be used by those w/ adv. Nitrox and deco training prior to getting a tri-mix certification.
On the surface, his logic for using heli-air makes sense, lower partial pressures of both nitrogen and oxygen seems to solve a several problems at once. That's what bothers me about it. It seems to make sense, but I've never heard anyone else mentioning it. Am I missing something fundemental here, or is something wrong w/ his thinking? BTW, the mix was being discussed in context of Great Lakes wreck diving in the 140-200 ft range w/penetration, doubles and a single deco bottle.
Thanks for your time.
Paul