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>I have seen several references to "O2 spikes" and Nitrox (a situation >were a diver breaths a fraction of O2 greater than the sum of a given >mix). Is this a real concern with Nitrox? I got my TDI Nitrox >certification this year and have used Nitrox on about 50 dives since. >I ALWAYS analyize my mix before EVERY dive, but if O2 does "seperate", >the odds of an "O2 spike" are very real! > >I recently went into the local dive shop where I get my Nitrox fills and >they were rolling tanks back-and-forth across the floor, "mixing the gas" >after a fill. This concerned me because I get my tanks filled with >EAN 32 & 36 and may not actually dive the tanks for 1 or 2 weeks. Will >the gases "seperate"? Should I physically "mix" the gas (roll the tank >around) before each dive? Will O2 stay in gasious solution? > >Thanks in Advance >Harry Jones >haj@te*.ed* >Padi DM-91974 Harry, Despite what others have said, the problem is not with the gases "seperating" with time (other than the potential loss of some He), but with them not being mixed well to start at the shop which in turn can screw up the anaylsis. By way of example: I own my own compressor, O2, and He tanks and do fills of Nitrox and Trimix with some frequency. My lower content O2 Nitrox fills such as Nitrox 32 or 36 usually come out as close to the mark as one can get; however, if I try for an EAN 80 fill and try to anaylze the mix just after topping off with air, I usually find I can get a reading as low as 50% O2. If I wait for several days the same bottle will read correctly. If I turn the bottle upside down, then right side up etc. several times, I'll get the correct reading. My assumption is that the O2 is sitting at the bottom of the tank, the compressor only fills at 6 cu.ft. per min. so the gas doesn't get "stirred up" by the topping off process. I've also seen the same thing happen in a dive store with a larger compressor, but once again only on a high content O2 fill like EAN 80. Same result. In fact, in our trimix class we did our own mixing and preparing for dives as you would expect. I found that we "threw out" some EAN 80 fills until we figured out what had happened. From that point on we took up the practice of mixing the high O2 content fills before analyzing the gas. Harold H. Gartner III 6900 Via Alba Camarillo, California 93012 home: (805) 482-9743 home fax: (805) 987-6804 office: (213) 487-6240 E-Mail: hgartner@ra*.or* CompuServe 71470,1423
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