Posted by Chuck Tribolet on June 03, 2005 at 20:25:13:
In Reply to: Oxygen below 100 feet posted by SoBay Jim on June 03, 2005 at 19:39:36:
The %O2 has two affects:
One is oxygen toxicity. One can debate whether the
max PPO2 should be 1.4 (187' on air) or 1.6 (218' on
air), but it's clearly deeper than recreational
limits (130') on air.
The other is narcosis and nitrogen loading, both of
which are determined by PPN2, which is determined by
F02 (everything that isn't O2 is N2, until you
start diving trimix and put He into the equation).
The math I posted showed that the PPN2 of air at
76' is the same as the PPN2 on Nitrox 35 at 100',
which Karl says is OK (I happen to agree that
the PPN2 is OK, I don't agree with his "best mix"
"you can dive all day on an 80" theory.)
So what's the right max PPN2? Dunno. It's a
religious argument -- there's little or now
scientific data. I know that photography gets
more difficult below 90' on Nitrox. But am I
unsafe? Or just wasting film? ;-)
There's also a long term O2 toxicity problem
because it doesn't seem to be a problem on
recreational Nitrox dives. You have to watch it,
but it never seems to actually get in the way, at
least for the profiles I do.
Chuck