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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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