BillyW,

Thanks for responding to that, you _did_ point out something I wasn't clear
about, but I have to respectfully disagree with you on another point.

1) Regarding CNS O2 toxicity

>>you got that ass-backwards<<
>>      2) In the water, if you run 1.6 for the whole dive, you
are more likely to take a CNS hit before you'll sustain pulmonary
damage.<<

No, but I did get it bass-ackwards <g>.

You are quite correct in that CNS 02 toxicity is _also_ time dependant. I
was extremely remiss in not noting that there is a CNS 02 'clock', and at a
pO2 of 1.6, the safe limit (NOAA) is considered to be 45 minutes. Anything
longer than that and the risk of CNS toxicity is unacceptably high. As you
even decrease the pO2 to even 1.5 or 1.4, your max exposure increases to 120
and 150 min, respectively.

>>in the chamber, where the likelihood of a CNS hit is lower, the
administration of a USN table 6 treatment, which includes a total
of 70 minutes at pp02 2.5 and a total of 2 hours at pp02 1.6
generally does NOT cause pulmonary oxygen toxicity. That's over
three hours at 2.5 to 1.6 WITHOUT 'burning' up your lungs.<<

Actually, it's 60 minutes (not counting ascent or descent time) at a pO2 of
2.8, and 2 hours at a pO2 of 1.9. I'm not counting the air breaks. Yes, the
likelihood of a CNS hit is lower, but more to the point, the consequences
are less severe - if a patient starts seizing, you just remove the mask and
have him go on air.

I would disagree with you on the statement that it generally does not cause
pulmonary O2 toxicity. A standard TT6 with no extensions will cause the
patient to accrue 642 UPTDs. This is above and beyond any UPTDs he may have
incurred through his dive (hopefully he kept his pO2 respectable). The USN
lists the max UPTDs per 24 hour period as 1425, but Rutkowski (Recompression
Life Support Chamber Manual, 1990) sources Lambertson and Wright as
suggesting a limit of 615, unless serious DCI is present.

I can only speak for USN chamber operations practices, and what Rutkowski
teaches, but they generally agree that two TT6s may be run in a 24 hour
period, but again, this approaching heroic measures. Again, the limiting
factor is the PULMONARY toxicity. .

 642 UPTDs correlates to a 2-3% decrease in Vital Capacity (basically lung
elasticity, which is used to guage the effects of pulmonary O2 tox), whereas
1425 is a 10% decrease. That's _alot_. Short term, mild doses, it is self-
correcting within a day or so. It _can_ lead to fibrosis of the lungs, and
permanent disability, though, with longer exposures. Perhaps this is what
you meant to say, instead of it doesn't cause it at all.

>>I think, if you are going to use these lists to think things
thru, you should clearly state that your ideas are just
speculation on your part. Otherwise, dangerous misconceptions
get started and spread around.<<

>> snip<<

>>Rich, if the consensus of smart people that you refer to ever
did exist, it would not argue against using 50 and 100%. And
it would not use the argument that "you are exposing your lungs
to high pressures of O2 with less of a benefit, since you still
have 50% N2 in the mix."<<

My apologies if you feel I was spreading disinformation. When I mentioned
"concensus of smart people", I was trying to say, in a humorous manner, that
while _I_ would not make a pronouncement on it, several other people have.
If you comb the archives, I think you will find a thread on this same
subject, that I read not too long ago. In it, people were labelled "strokes"
and "morons" for using 50/50 mixes to deco. I prefer to keep my discussions
professional, but I stand ready to be corrected if indeed, I am misinformed
about something.

>>50% is a useful decompression gas. Waiting till you are at 6
metres before applying a high pp02 (1.6) as you would have to
with 100% as your only deco gas, does not make good deco sense.
You should take advantage of the oxygen window right where your
decompression goes from being depth dependent to time dependent.
50% does it nicely.<<

OK, so you _are_ advocating using _both_ 50% and 100%? That seems to be at
odds with the other thread I mentioned, but like I said, I was attempting to
show that information as not being my own, but garnered from another
discussion. Are you using air or trimix? Perhaps my confusion stems from the
fact that the other thread was (I believe) in reference to deco after
trimix, where the diver may already have shifted to a gas richer in 02
content for his ascent. Or maybe it was felt that the logistics of requiring
an extra cylinder wasn't worth it. I will attempt to find that in the
archives again. Let me know if you want me to send the message numbers.

>>Rich, there are some very good texts on decompression theory
and practice which will help clear up a lot of your confusion.....
Also check the archives here. George Irvine has consistently provided a
stream of very useful information based on the WKPP's successful regimen for
decompressing from deep
exposures, long and short - the stuff that really works.<<

Already read them, in addition to some of Lambertson's stuff, and Bove. As
for the stuff Irvine has posted on the deco profiles of the WKPP, I have not
found that, but I _will_ go back and look, because it sounds like exactly
the type of info I'm interested in (for intellectual purposes only, I have
not done a deco dive in awhile).

Thanks again for pointing out my ommision from the previous post.

Rich L

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