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Jess You will most likely be much safer using less than 1.6 ATA po 2 at deco. The reason IANTD in 1991 started encouragement of EAN 80 was to reduce the deco po2. We did not do this because we thought there may be a problem, we did it because several divers did have problems using o2 at 20 feet. As you know there have been o2 hits on o2 at 20 foot. To my knowlege no o2 hits have taken place on EAN 80. I do not know of anyone getting bent using EAN 80 and in my own plus my students and numerous other IANTD instructors and students dives alone we can document thousands of dives using EAN 80 for deco. In caves it is not as much of a problem as the 20 foot stop is usually stable. In open water divers tend to stay slightly deeper than 20 feet and if they are as deep as 23 it is 1.7 po2. On all models that I'm aware of there is little difference in deco time but a lot of difference in the o2 loading between EAN 80 and o2. I have no doubt that from a deco standpoint there are advantages to pure o2 and in mixing it certainly is much simplier, but do the advantages outweigh the risk. For me they do not. George once posted that he had started putting a little air on top of his o2 due to tox risk. I know in personal communication that this followed a dive where he experienced some symptoms of o2 tox. I do not know if he is still putting air on top of his o2 or not. From his response to you I guess he has gone back to pure o2. Tom Mount You wrote: > >Re.: Using 80% O2 for deco vs 100% O2 > >Apalogies if this has been covered already, but I was taught that on certain >profiles, e.g. those with a pretty good 30 foot stop, that there were often >advantages to using 80% vs 100% O2. The increased efficiency of 80% O2 @ 30 fsw >(versus air or 36% or 35%) makes up for the decrease in efficiency @ 20. Also, >as has been mentioned, the O2 tox count goes WAY down, more than you can >imagine, on 80% versus 100% @ 20 fsw. The software on which I have had access, >Abyss, ProPlanner, DrX and Decomp all bear this out. The deco will be longer >with 80% but usually by only about 1-3% of the total deco time (2 to 5 minutes >on a two hour deco) and the total %CNS can be reduced by as much as 1/2. >Frankly, I think 80% has many advantages and have not heard any real >physialogical disadvantages. I am sure someone out there will quickly correct >me if I'm wrong, however. > >When diving with a group, however, it is always better to have all the same >gasses all around. For example, when diving with WKPP or Key West Divers, where >support divers are watching the gas switches, there needs to be only one method. >Also, no tank mix-ups are possible. > >Comments? > >Jess > > >
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