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John Dunk wrote: > > On Sun, 23 Nov 1997 16:50:04 +1000, you wrote: > > > 4) In this same interest you will find that when you graduate to real > >diving, as in caves, you will not want to accellerate your ppo2 at > >lower depths while still being faced with a long decompression at > >shallower depths, and making bizarre mixes to do this is a dangerous > >mistake (just like the fantasy of holding an accellerated ppo2 on a > >rebreather throughout a deco). I am anticipating the thinking that the > >80/20 crowd would then go to an additional oxygen in cave without > >accounting for total exposure, and subject themselves to the risk of tox > >in the final deco steps. Tox you do not get out of - bends you do. > > Would someone explain' the "fantasy" of holding an accelerated ppo2 > on a rebreather throughout a deco ' and why it's a fantasy?Are we > talking tox here or what?And how does 80/20 supposedly help divers > with poor buoyancy control? Hope I didn't come inb too late on this > one. Also, someone mind listing the claimed benefits of 80/2?. > Thanks > > John Dunk o > Tallahassee,Fl o > screwloose@el*.co* ____o_____ > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. To address the bouyancy issue soley, the gas choice does not affect bouyancy. The diver's lack of bouyancy skills forces them to use 80/20. A diver who has poor bouyancy control would find it easiest to do a O2 deco stop at 20 feet/6 meters rather than at 10 feet/3 meters. This diver will then want to use 80/20. This is a wrong reason to be using 80/20. The correct thing to do is learn and practice correct bouyancy control. The reason it is easier to do an 02 stop at 20ft is that there is less of a preasure differencial there than at 10ft. At 10ft if you inadvertantly move up a foot to 9ft you will be more positively bouyant (from the resulting expansion of your dry suit or BC) than if you moved up one foot from 20ft. to 19ft. This diver with poor control could find himself very quickly at 8ft. and unable to recover, ending up at the surface with omitted deco. The greater differential at 10ft. also means that changes in body orientation and attitude (prone to kneeling) will cause bouyancy changes, which may not manifest at 20ft. Thus, if the diver is at 20ft becuase they are not confident about their bouyancy control, they would not choose pure 02. 80/20 has a p02 of 1.28 at 20ft., giving the diver the margin of error needed to stay within limits. Divers doing deco at 10ft on pure 02 have 20ft margin of error, they can inadvertantly drift 20ft deeper before the p02 approaches anything worrisome. The diver doing deco at 20 wants the same margin of error. It neccesatates mixing to 80/20. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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