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post #21 of 25 Old 01-08-2007
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"The object of diving gas mixtures is to reduce the oxygen fraction"
The object of what mixtures for what purposes?
In sport diving, the object was to neither reduce nor enrich the percent of oxygen, but to use standard air.
But standard air "is" close to an 21% oxygen 78% nitrogen mix, and for some 20 years now sport divers have been using oxygen ENRICHED air mixes under some trade names like Nitrox(r). By enriching the oxygen content (raising the percent) you can easily decrease the nitrogen and associated problems of the bends, while still avoiding the problems of oxygen toxicity (and outright flammability) that start getting very much worse around 40% oxygen.
Thw two "standard" Nitrox mixes give you, roughly, one more group each in the decompression tables, or that much more safety if you use those mixes with the old air tables, because they have less nitrogen content and not enough oxygen to become dangerous.
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post #22 of 25 Old 01-08-2007
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hellosailor is obviously a diver as I am.
I do dive Nitrox and the point is that when you fill a nitrox tank you use 100% O2 to a partial pressure of say 1000 psi. the balance 2500 psi is then filled with air so you end up with a 02 content of say 32%. It's that initial partial fill of 100% that I wonder if the composite material will react to. As Hellosailer stated, o2 over 40 % and hydrocarbons react badly. The composite material is made from hydrocarbons. Is it inert in that state? I don't know. But thats besides the point almost all of the divers I know couldn't afford a compposit tank anyway.
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post #23 of 25 Old 01-08-2007
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Sorry about that, I misread the post. Pure O2 is still for aviators, though.
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post #24 of 25 Old 01-08-2007
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Easy to misread. Heck, the Nitrox folks would have you believe they bottle magic, as opposed to the folks who just call it "oxygen enriched air". Aviators got it easy, at normal air pressure oxygen is way less toxic.

How many Nooze Reports still talk about SCUBA divers and their "oxygen" tanks? And they've got staff to check on that kind of stuff. Me, I've got gills. I just take the tank down so I don't scare the locals.
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post #25 of 25 Old 01-09-2007
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I would suspect all of the concerns raised would be concentrated in one area of a composite dive tank; the FRP to regulator receiver coupling. At some point you have to put a discharge orifice on the tank and heat, high pressure, abuse, and intended use are all going to expose any inherent weaknesses in the design. BTW, the less symetrical the tank the weaker it is going to be. With propane tanks being nearly spherical and scuba tanks being quite elongated I'm sure there are issues with the higher pressures used in them.
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