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Re: Enriched Air (was Re: TEST YOUR KNOWLEDGE)

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Tue, 21 Sep 1999 10:28:42 -0400

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 ```Ed Graves wrote: > > Haven't taken the class yet, but it sounds like you > have a good point Art. > I got to thinking about what I wrote & how the other > diver used his pony on every safety stop. In this > case he uses a 19cf pony with a 40% mix. He does 5 > dives & 5 safety stops, of at least 3 minutes. You > can't get EAN on the island we were on so no chance of > re-filling the pony. We were doing fairly deep dives, > 80 - 100fsw, if he had had to use the pony in an > out-of-air situation, let's say at the beginning of > the 5th dive, chances are he wouldn't have had much to > work with. > Thoughts? > Ed   Let's do the math. 4 safety stops of 3 minutes each is 12 minutes total. He's at 15' (let's say 1.5 ATA for round numbers). If we use the round number of 1 cu ft/minute as his SAC then his rate at 1.5ATA is 1.5 cu ft/minute and he would have used up 18 cu ft on the pony - it's virtually empty (157 PSI left if it's a 3000 psi pony). But, if we use .75 cu ft/min as his SAC then he would only have used 13.5 cu ft as of the end of his 4th dive, leaving him with 5.5 cu ft (868 PSI). That's enough to get him out of a small jam, but as far as I'm concerned a 19 cu ft pony is the absolute SMALLEST pony that's usable. I much prefer a 30 (typically 33 cu ft) or 40 (which is what I have) cu ft pony.   If you want to use it as an O2 bottle, then an LP steel tank is better because O2 is typically only available around 2200 PSI. There are 45 cu ft LP steels available that are a nice tank for that purpose.   By the way, for the person who said they wouldn't use nitrox until they were trained for it... Air *IS* nitrox, by definition :^) What you should have said was that you wouldn't use EAN (enriched air nitrox) or, even a bit more sublte, non-normoxic nitrox (i.e. a nitrox mixture OTHER than 21/79) :^)   Carl ```