O2 Toxicity in deco question

[Merida Cave Diver]

The other day I did a fairly long dive where my deco time was 96 min. My CNS was fine up until the very end when it went up to 102% for the last minute or two. In looking at my dive chart which made sense, it started really climbing when I switched to 50% NOX and then my 100% mix for obvious reasons. Knowing that the computer is working on an calculation vs gas analysis I confident that there's wiggle room in there, plus I added some air breaks but my question is this...

You have 5 min left in your deco stop according to your computer and you're at 3m. You're at 99% O2 Toxicity.... what do you do?

A. Continue deco on your O2
B. Continue deco but switch to air
C. Abort the dive and surface

Curious what thoughts and opinions are out there. Anyone have direct experience with this?

 

[davehicks]

D. Spend 96 minutes thinking about what CCR model you'll be getting to avoid such long deco times

 

[Jack Hammer]

Air breaks

 

[grantctobin]

D. Spend 96 minutes thinking about what CCR model you'll be getting to avoid such long deco times

That’s literally not how that works…

 

[rddvet]

You're at 99% O2 Toxicity.... what do you do?



Curious what thoughts and opinions are out there. Anyone have direct experience with this?

It's the oxygen window, not oxygen toxicity %. I can be triple that and not die. So there's a big difference in what those terms suggest. I would think being a ccr diver this should have been discussed in depth for you to get to this point, so I'm surprised by the question. My answer: I don't really care so the answer is A. The difference between 99% and 100% on the oxygen window means absolutely nothing. If I've been taking appropriate oxygen breaks (usually I just let my p02 degrade, then bump it back up), then I don't really care what % of the oxygen window I'm at. I honestly pay pretty much zero attention to it.

 

[DiveTucson]

I guess I’m lucky I’m still here after the diving I did this week…

 

[Akimbo]

My CNS was fine up until the very end when it went up to 102% for the last minute or two.

Having exceeded the current recommended limits for pulmonary OxTox MANY times when the limits were lower, I would not worry about a few minutes. IMO, not worth a gas switch.

 

[Alaskan Scuba Dude]

Switch to a lower O2 percentage.

 

[PfcAJ]

OTU, CNS %, and the “oxygen window” are 3 separate things.

OTU and CNS% describe oxygen exposure limits. OTU is related to pulmonary toxicity and CNS is related to nervous system effects.

The “oxygen window” refers to increased po2 for deco.

CNS% is a very poor indicator for oxygen exposure risk. Hitting 100% doesn’t mean you’ll tox. Divers have exceeded that limit and racked up thousands of percentage points and been fine. Conversely, you can tox below “100%”.

Things that work? Low po2 on the bottom, max po2 of 1.6 when resting on deco, gradual reduction of po2 as you ascend, and gas breaks when on high po2 gases.

 

[broncobowsher]

You finish the dive. Run past the 100%. Probably pass on the next dive of the day. go on with life.
Check your dive planning, adjust for next time.

100% doesn't mean that is as far as you can go. I still like the last helicoptor ride I took. The tachometer reads in percent, not RPM. Take off speed is something like 104%.