Mailing List Archive Mailing List Archive
yup -- wasnt that covered in you training program? At 09:42 PM 11/23/1998 -0000, you wrote: >Ok, so 100% oxygen is the way to go. What do you do about "airbrakes". > >When, i.e. after 20/25min? >for how long, i.e. 5/10 min? >And what gas do you use for "airbrakes" i.e your 50%, your 36% or your >bottommix? > >Mike > > > >-----Original Message----- >From: Joel Silverstein <joelsilverstein@wo*.at*.ne*> >To: gwaw@ix*.ne*.co* <gwaw@ix*.ne*.co*> >Cc: Techdiver@aquanaut.com <Techdiver@aquanaut.com> >Date: 23 November 1998 16:23 >Subject: 80% arrrgh!! was Re: On the left > > >>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'. >> >> > > > 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'.
Navigate by Author:
[Previous]
[Next]
[Author Search Index]
Navigate by Subject:
[Previous]
[Next]
[Subject Search Index]
[Send Reply] [Send Message with New Topic]
[Search Selection] [Mailing List Home] [Home]