o2pp 1.4ata+?

[Rick Murchison]

Regarding CNS vs pulmonary toxicity, I was under the impression that the oxygen exposure tables are for pulmonary toxicity, and that the way to avoid CNS toxicity is to not dive past the "limits". Does anyone have any concrete evidence about this?

Which table?
The "CNS Clock" table is designed to avoid a CNS hit.
The "Repex" table for tolerable exposures is designed to prevent pulmonary toxicity problems.
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There's an awful lot we don't understand about oxygen toxicity; if you dig around you'll find that there are divers violating just about every rule we have, routinely and successfully - but in very specific controlled ways.
For recreational Nitrox diving, the recommended limiting PO2 is 1.4 ATA; the maximum limiting PO2 is 1.6. Divers should plan the diving day to not exceed 80-90% of the CNS clock, and allow an hour between any two Nitrox dives.
Don't push it.
Rick

 

[Wijbrandus]

While I have no problems with a 1.6 ppO2, I will keep my 1.4 as a planned depth.

It's not that I think higher percentages are really that unsafe. I understand how the numbers keep dropping in response to knuckleheads doing kuckleheaded things. It's simply my supreme confidence in all the the negative karma I've accrued in my life coming back to haunt me at that one particular moment...

Basically, OxTox is so bad that I really don't want to risk it, and if 1.4 is where the risk is mitigated enough to be considered "safe", then that's my limit.

I certainly won't hesitate to use the 1.6 "contingency" limit, and in an emergency I will accept a 1.8, or even a 2.0, but it had better be a good reason. I won't tread that deep for anything short of a life or death matter. I'm not trained past 100' anyway, so I've got no business going there.

 

[MikeFerrara]

The CNS clock isn't all that predictive where time measurements go from what I've read and from my own experience. As PPO2 goes up so do the chances of a hit. the curve is not linear and somewhere at or below 1.6 hits almost never happen and somewhere above the curve rises steeply. At higher PPO2's divers in tests toxed at widely varrying times but tox they did. That's why I say that time isn't that great of a predictor.

If I recall there are some studies referenced in the IANTD "Technical Diver Encyclopedia" but I'll leave it to folks to look up studies because I have to go feed the horses. LOL

 

[matt_unique]

I plan all dives not to exceed 1.4 on the dive and deco up to 1.6 and I never exceed 75% of my O2 clock.

Ditto for me....

--Matt

 

[Don Burke]

Nitrox divers. Do you or will you ever exceed 1.4ata?]

I go to 1.6 for deco for short periods.

Would you bop down to 1.6 to get a picture?

no

Or 1.8 to get the light you dropped?]

no

Or maybe you don't have a problem planning dives to 1.5.

I do.

Would you dive 32% to 120'?

no

Why?

n/a

Why not?

Oxtox is rather unpredictable and I find the small additional risk unacceptable. If I need to do deco stops, I will do the deco stops. I will not jack the oxygen up on the working part of a dive to get out of a few minutes of deco.

 

[Land Locked]

This is an interesting article I found when I was getting my Nitrox certification,
http://www.sportdiverhq.com/po2s.pdf
I'm conservative and I'll leave the high P02's to the tec'ies of the world.

 

[Kim]

This is an interesting article I found when I was getting my Nitrox certification,
http://www.sportdiverhq.com/po2s.pdf
I'm conservative and I'll leave the high P02's to the tec'ies of the world.

That's a good article!

 

[Stone]

There are a number of wrecks in our "Wreck Alley" that vary in depth from 110 to 135 fsw. I mix 30% for this area. On the deeper wrecks, we hit 1.5 PPO2 for short periods when looking for fish and lobster under the stern and bow, but most of the time we are on the upper decks where the PPO2 is closer to 1.4.

 

[Uncle Pug]

Nitrox divers. Do you or will you ever exceed 1.4ata?]

I go to 1.6 for deco for short periods.

Would you bop down to 1.6 to get a picture?

Yes

Or 1.8 to get the light you dropped?]

Maybe... to get the light you dropped.

Or maybe you don't have a problem planning dives to 1.5.

I don't plan dives to exceed 1.4 but allow for it.

Would you dive 32% to 120'?

yes... but I would prefer 30/30

Why?

Because it isn't a problem for short exposures as far as I am concerned. 30/30 so I could remember what I saw there.

Why not?

There are precautions I take, like not staying long and not over exerting. If it were not possible to take those precautions then I wouldn't.

 

[StSomewhere]

According to my training (IANTD), its meaningless to talk about pPO2's without also talking about time. My training stressed the NOAA CNS limits of 1.6 for 45 minutes, 1.5 for 120 minutes, 1.4 for 180 minutes. This assumes ideal conditions (not cold, not a working dive, no real current, etc.). It should go without saying that I'm obviously responsible for determining/adjusting my own pPO2 based on actual conditions, times, etc. An ata of 1.4 is not a magic number.

Do you or will you ever exceed 1.4ata?

Would I *plan* a dive to 1.6, nope. Would I plan a dive that allowed for a *contigency* of 1.6, yes, sure, but that's my limit.

Would you bop down to 1.6 to get a picture?

Sure. For a few minutes if conditions were right.

Or 1.8 to get the light you dropped?

Just how much did I pay for that light? My guess is, probably not. I lost a not-yet-inflated safety sausage in a current last month and let that go rather than leave my buddy and the down line to chase after it.

Or maybe you don't have a problem planning dives to 1.5. Would you dive 32% to 120'?

I very well might, considering the conditions and how long I planned on being at that depth. At the risk of opening myself up to ridicule, I'd probably want to get my rec trimix cert and dive 30/30 or 25/28 for >100' but to be honest other training is currently taking priority.

***Warning. Only dive mixed gases based on the certifying agencies guidelines, not based on what people on Scubaboard say, or you will die "a horrible death.

I believe everything I read on the Internet, ever since Al Gore invented it.