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Dear Arnie, It is quite easy to pump 100% oxygen to 3000 psi -- the dive shop needs to make the investment in a proper oxygen service rated Haskel Gas booster. Most any reputable dive center who is mixing gas for the consumer should have one, anyone that does not should step up pet the pony and buy one. 80% EAN was not created from a decompression standpoint it was justified by those who did not have a gas booster. Here's why. Oxygen gets delivered in 2400 psi bottles, (some major cities have gas suppliers who can supply at 3500 psi) however you can cascade into a 3000 psi rated cylinder about 2250 psi of oxygen top up to 3k with air and you have 80% oxygen content. Simple enough. However ....... 80% EAN limits you severely. 1. at 20 and 10 fsw its PPO2 is too low make it useful, at 40 fsw its too high for maximum exposure limits. 10 fsw 1.04 po2 too low 20 fsw 1.28 po2 too low 30 fsw 1.53 po2 borderline 40 fsw 1.77 po2 too high Where as 100% oxygen is 10 fsw 1.30 po2 20 fsw 1.61 po2 (with the 10 fsw stop normally being taken at 20 fsw Advocates of the EAN80 (a/k/a stroke mix) have come up with a variety of reasons to justify not using 100% oxygen --- one of the great ones is "its good for divers who have trouble holding buoyancy at 10 and 20 fsw" frankly if a technical diver cant hold a 20 fsw stop --- they should go bowling and get the hell out of the water. Most divers who are using accelerated decompression tables have standardized on their decompression mixes. (some are finding that hyperoxginated heliox mixes are working well too though that is beyond the scope of this email) EAN 36 from 110 fsw EAN 50 from 70 fsw 100% oxygen from 20 fsw Granted when you run one of the consumer dive profiling softwares you may see only a small decrease in decompression time -- maybe 5 minutes by using 100% over EAN80. and though you may belive that is not a significant enough advantage to make sure you have 100% oxygen here are a few more non-scientific reasons. From a mixing standpoint unless you are using exceptionally clean hyper filtrated air or air produced from an oil free compressor there is risk of explosion when mixing high pressure air on top of 100% oxygen. It probably has not happened yet --- but some day some goober will blow up a building doing it. Even if you are using a 30 cuber (small) just cascading 2400 psi oxygen in it will give you 24 cuft of oxygen -- for deco thats easily 40 minutes worth, which is a lot of gas. No need to goober around making EAN80 for the other 6 cuft, its just too much work for it and I am sure it costs a bit more, besides if you are doing a dive that requires much more than 40 minutes of oxygen decompression you would want a bigger tank. The fact that a tank has a pressure rating of 3000 does not mean you have to fill it to that level. I have an excellent tank chart for all currently available tanks in the US on our web site - go look at it. Next; most consumer available oxygen analyzers using electrochemical sensors can be off by as much as 2% in their readings, so is your 80% really 80 or is it 78? Whereas pure oxygen is upwards of 99% pure -- it's a known item. Arnie, as a techie in training you have an opportunity right in front of you. It's two roads ... the left road is filled with exploration, friendships, technology and long proven safety procedures. The right road is bumpy, full of mis answered questions, body bags, and strokified convolution. I get the feeling your want to take the high road and do it right. In Judaic studies we are taught to ask why not to follow blindly. So in this very long winding response (If I had more time it would have been shorter) the answer is .... EAN80 buys you 6 cuft more gas, but buys you nothing else. Take no shortcuts when it comes to technical diving. Good Luck At 10:21 PM 11/22/1998 -0800, you wrote: >Joel, > >Another question for you. It is prompted by your post on the bottle >marking issue. > >What is the advantage of 100% O2 compared to 80% O2. I've been using >the latter for deco. For one, it is somewhat easier to get at local >dive shops because it is harder to pump the 100% to 3,000 psi, but that >is merely convenience. More importantly, I can get on the 80% at 30ft >and have the advantage of breathing a higher gradient gas mix sooner >than waiting to the 20ft stop. The published tables I've seen give no >time advantage to doing deco on 100% over 80%. > >What is your view and why? TIA. > >Blow gentle bubbles, > >Arnie >Tech Diver in Training > Joel Silverstein Scuba Training + Travel Co. http://www.NitroxDiver.com -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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