Will - right on the money. Yes, we have noticed the oxygen nacosis, but
guess what - we were diving it too deep anyway. Good points in this
post.

Here is how we found it ( other than suspecting it for obvious reasons
in the first place): we have a dive that goes 3500 at 120, another 1700
at 150-179, drops to 240 for 600, and then 310 from there on. We are
diving two nitroxes to the dropoff, using them as deco on the way back,
with the 310 gas on our backs. The first bottle was ok, but the second
was only 24%, and we had nothing but trouble with it. One diver tried to
call a dive over a freeflow that was not happening, JJ and I dumped our
bottles in a crack, we had numerous clsuters at that bottle drop going
in, but we could see that coming the other way on gas back to them. We
had been using air for the second bottle and could tell a differnece
just between the air and the nitrox. We stopped doing that, and just
started adding helium to the gas - bingo.

We now go wtih a 1.4 ppo2 , 100 aed for that situation. This allows us
to pull the last bottle back over the dropoff and give it a 1.6 resting
set of stops before moving on. 

We are talking a bunch of tries at this to finally see the story, but as
you point out, we all know better now. Thanks for being a voice of
reason among a sea of blithering idiots.



William M. Smithers wrote:
> 
> I've gotten a couple (out of a couple hundred) emails from
> ZPlan users requesting that O2 be considered narcotic as
> an option in future versions.  I'll probably chuck it in,
> just because it's a trivial computation, but this got
> me thinking about the whole O2 narcosis issue, and I'd
> be interest to hear some informed opinions.
> 
> While I certainly realize that there's a fair amount of
> research that indicates O2 may very well be
> narcotic, my current thinking is that the whole issue is
> basically irrelevant anyway.  Here's why:
> 
> [1] O2 is theoretically about as narcotic as N2, so as
>     you dial down your PN2 in a Nitrox, the narcotic potential of O2
>     increases accordingly, so for Nitrox/Air it's a totally
>     moot point.
> 
> [2] Narcosis is not usually considered a problem by most
>     divers in the Nitrox (well, EANx) depth ranges.  So again,
>     it's a meaningless concern for Nitrox.
> 
> [3] In the Helium-addition depth ranges,
>     PO2 is fundamentally limited by toxicity concerns, and thus
>     any O2-enduced narcosis is constrained by the fact that your MOD
>     limits the FO2.
> 
> [4] In the trimix/heliox range, the selected PO2 is
>     likely to be the same, or less, than that selected
>     for the Nitrox range, so the O2 narcotic potential
>     is a relative constant, and amounts to only a small
>     fraction of your total END.
> 
> For example, let's say we're doing a trimix dive and wish
> to dial in our END and PO2, and fill the gap with Helium,
> and we want a max END of 130ft and a max PO2 of 1.4.
> 
> At 130fsw on air, your PO2 is about 1.0 and your PN2 is about 3.9,
> for a total "narcotic partial pressure" of 4.9 (assuming O2 is narcotic).
> Sticking with a max PO2 of 1.4, and a max PN2 of 3.9, the difference
> *at any depth* in narcotic potential for an END of 130fsw, if you assume
> O2 is narcotic, is .4 P(total narcotic gas), which is about 10 feet of
> Equivalent Air Depth.  And for 10ft of EAD, I'll bet most divers
> will opt for the deco advantage of the additional .4 PO2.
> 
> So basically, like I said, I think the whole O2 narcosis issue is
> irrelevant to actual diving, and best left for academia.  Sad part
> is, it's easier to put the "O2 is narcotic" switch into the software
> than to include this long-winded explanation as to why I didn't.
> 
> -Will
> 
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