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Jim has hit one of the nails on the head here. Anyone doing their deco = on 80/20 from 30 feet as opposed to 100% from 20 feet is still going to be facing a similar PPO2 for similar times. They are going to need backgas breaks in the same way that those using 100% will need backgas breaks - = that is if their deco goes for long enough to need backgas breaks. So much = for that argument! =A0 Have I got it wrong, can anyone tell me why the 80/20 crowd will not = need backgas breaks? =A0 Regards Steve Bliim Still waiting for my trip to the NE! -----Original Message----- From: Jim Cobb [mailto:cobber@ci*.co*] Sent: Saturday, 2 September 2000 1:33 To: Guy Morin Cc: Tech Diver Subject: Re: 80/20 deco So what you are telling me that you will use whatever it gets you out = of the water quicker, damage to your body be damned, and whatever I say or = anybody else says will not make you change your mind. I don't know what it takes to get you guys to realize that the idea = with deco is to remove nitrogen from you body and you don't do this by = breathing more nitrogen. Nitrogen is what causes the damage. I also, IMHO, your thinking is flawed when you presume that using 80/20 obviates the need for air breaks. Seems to me if you are doing *any* = mix where you are spending extensive time at 1.5 PP02 or above you would = want to do air breaks to avoid long term damage to your lungs.=20 Oh, yeah, the only thing that matters is getting out of the water fast, = I forgot. =A0=A0Jim ------------------------------------------------------------------- Learn About Trimix at http://www.cisatlantic.com/trimix/ From: Guy Morin <xnet@vi*.ca*> Date: Fri, 01 Sep 2000 09:24:54 -0400 To: Jim Cobb <cobber@ci*.co*> Cc: Tech Diver <techdiver@aquanaut.com> Subject: Re: 80/20 deco Hi Jim,=20 Thank you Jim for confirming what was elucidated=20 in the post. For myself, you are quite right that I will=20 be using the theoretical model since it has a good=20 track record, and consistently estimates what I am=20 actually diving. Doesn't the WKPP have something=20 in regard to diving to what is planned? I would have=20 to guess not, since they never dive what they plan.=20 Only a fool would dive following the WKPP method=20 without knowing all the details of what they practice,=20 and that certainly isn't available on the net, on this list,=20 or through word of mouth.=20 As far as your practice versus theory, well that part=20 is going to be ignored the WKPP obviously hasn't=20 put in the same effort in 36/80 deco as it has in 50/100.=20 On another note, remember that it is someone who was=20 promulgating the WKPP method as being superior that=20 pointed out the tissue loading from the theoretical model,=20 not me. Let's keep that little detail in mind, shall we? He=20 who lives by the sword...=20 Finally, I will point out that from a logistical and consumables=20 perspective, 50/100 deco does make better use of resources.=20 If I was wanting to get hundreds of divers through the water=20 to stage a big push, that would be my choice too. The major=20 costs for a large operation is gas consumables. Using 36/80=20 deco requires a greater investment in blending, and gas=20 matching, and wastes a lot of gas. The reasons are obvious,=20 getting off back gas at around 100' prevents the back gas=20 from getting drained as would be the case in 50/100 deco.=20 Using back gas in deco allows it to be drained following more=20 liberal rules than thirds. In addition, since shallow deco allows=20 switching to back gas, that makes further use of back gas,=20 and economizes the O2. Using O2 is simple to blend, and=20 is insensitive to error. Since a lot of time is spent at the=20 shallow stops, not having to blend huge volumes of gas,=20 and the subsequent analysis required, and schedule tweaking,=20 it makes a lot of sense, especially on that scale.=20 So, from an operational standpoint, 50/100 is by far the best=20 choice. For the diver who doesn't have to worry about consuming=20 millions of cubic feet per year, and who wants accurate deco=20 estimation in a field environment that often does not afford=20 the luxury of a decompression chamber, something more "consistent"=20 makes a lot of sense.=20 --=20 Guy =A0 -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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