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Arnie, Something Joel forgot to mention is that if you need O2 for a medical emergency, and you are using 100% O2 for deco, you already have the right gas there with you. Nanci At 10:14 AM 11/23/98 -0500, Joel Silverstein wrote: >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'. > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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