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One of the arguments divers use to justify the use of 80/20 mix is that it is "safer" to use 80/20 because of buoyancy issues. As you know, 20' for 100% oxygen has a higher PO2 (1.6) than 80% (1.3) and because of this people are concerned loss of buoyancy can put the diver into high PO2 situations. The reply to this argument is that you need to be able to control your buoyancy in the water column. You need to practice your ascents and deco stops until you can nail your buoyancy anywhere in the water column. Using 80/20 as a deco gas for added safety is a poor substitute for good skills. Summary: From the arguments presented in these postings, it can be shown that the benefit of opening the O2 window as far as possible exceeds any perceived added safety obtained from using 80/20. Kurt > Hi All, > > in the politically incorrect "Deep Diving", Brett Gilliam recommends the > use of oxygen for exactly the same reasons. DIR agreeing with something > Brett said? Surely not. > > -----Original Message----- > From: mikey@ma*.co* > Sent: Thursday, March 23, 2000 10:30 AM > To: bem@be*.ne* > Cc: techdiver@aquanaut.com > Subject: Re: 80% vs 100% > > << File: ENVELOPE.TXT >> > -------------------------------------------------------------------------- > -- > At 10:12 AM 3/22/00 -0500, Brian McMillan wrote: > > Hello Brian, > > >In one of Max's rants over the past couple of days he made a comment > about > using multiple mixes for deco (including 80% O2 as opposed to 100%). I > understand from a physiology standpoint why deco is more effective on > 100% > O2 then 80% O2. What I don't understand is why most people are opposed to > using it. In models I have run deco on 80% works (mathematically) and in > general doesn't extend deco time too much. > > > >I have been taking it on faith that I should be using 100% at 20' and > above. Can anyone tell me the science behind it? > > There are a bunch of good reasons for using 100% O2 instead of > 80%. Here are a few I can think of off the top of my head: > > 1. The oxygen-window is as open as possible with 100% O2 especially > at the 20-foot stop. Now you're gonna ask what the heck is > an oxygen-window, right? It's not a complicated subject, but I > don't have time to do it justice now. I get asked this all the > time, so it's probably worthwhile to write something on it. I'll > do that in the next few days and email you a copy. For now, let's > just say that 100% O2 will allow you to off-gas faster then > straight Buhlmann (and intuition) says you should. In fairness, 80% > does too, but it's disproportionately less efficient and has other > important disadvantages. > > 2. If you have to bail out part-way through your decompression, > breathing 100% O2 on the surface may allow you to walk away > from it depending on how severely you violated your decompression > and how good a shape your body and lungs are in. On most 'bounce' > dives, you might skip your 30, 20, and 10-foot stops and still have a > fair chance to get away with it if you breathe 100% O2 on the surface. > Not so with 80%. Omitted stops can happen when diving in the ocean > when weather or other circumstances require it. > > 3. If you do get DCS while breathing 100% O2, you're *already* > administering the universally accepted treatment while awaiting > transportation to a chamber. The last thing you want in your > DCS treatment gas is 20% Nitrogen, the very gas that's hurting you! > > 4. While it's true that you won't get the full rated volume of your > deco bottle when you fill it from typical O2 supply pressure, > you actually end up saving money with 100% O2 because you'll never > have to dump a partially-full 80% bottle to remix a new batch; you > just top-off with O2 each time. Besides, there are better places > than your life-support system to save money! > > 5. If you always use 100% O2, you can permanently mark your bottles > and not have to wonder if the wrong analysis sticker got put on the > bottle. A side benefit is that you can standardize your gases. > > How's that for starters? > > -Mike Rodriguez > <mikey@ma*.co*> > Pn(x) = (1/(2^n)n!)[d/dx]^n(x^2 - 1)^n > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > __________________________________________________________________________ > ____ > __ > This message has been checked for all known viruses by the Star Screening > System > http://www.star.net.uk/stats.asp > > > > > > Visit our web site at www.scott-wilson.com > > Privilege and Confidentiality Notice. > This e-mail and any attachments to it are intended only for the party > to whom they are addressed. They may contain privileged and/or > confidential information. If you have received this transmission in > error, please notify the sender immediately and delete any digital > copies and destroy any paper copies. > Thank you. > > > Scott Wilson Scotland Ltd > Registered in Scotland No. 48951, > Registered Office: 6 Park Circus, Glasgow, G3 6AX. UK. > > ________________________________________________________________________________ > This message has been checked for all known viruses by the Star Screening System > http://www.star.net.uk/stats.asp > > -- > 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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