Air Breaks and CNS

ianr33 · Mar 3, 2013

I've only ever done a handful of dives that were pushing CNS limits, so this is a theoretical question.

Lets suppose I do some monster dive and end up needing a couple of hours at 20 feet. That's going to be way over 100% CNS.

Assuming I do normal air breaks (12 on 6 off, or thereabouts) will I (probably!) be O.K. ?

Presumably that's how the WKPP guys survive??

Superlyte27 · Mar 3, 2013

The air breaks have nothing to do with CNS. They have to do with burning your lungs.

ianr33 · Mar 3, 2013

So how do people blow away CNS limits and live?

nadwidny · Mar 4, 2013

Superlyte27:
The air breaks have nothing to do with CNS. They have to do with burning your lungs.

They have as much to do with CNS as they do pulmonary.

Dsix36 · Mar 4, 2013

It is a bit of a double edged sword. As Your CNS builds during deco, you might consider taking air breaks to lower your O2 intake. This will add to your overall deco time since you will not be offgassing as effectively. By the time that you are finally cleared to exit the water your CNS can still climb to very high levels.

As already stated it will make a big difference in how crispy your lungs get. There is also the very real concern of oxygen toxicity during long periods of O2 use.

Some of these decisions are going to have to be made by learning and understanding all of the risks involved. This really is not something to try to figure out from a forum.

nadwidny · Mar 5, 2013

Dsix36:
It is a bit of a double edged sword. As Your CNS builds during deco, you might consider taking air breaks to lower your O2 intake. This will add to your overall deco time since you will not be offgassing as effectively. .

Only if you are a slave to your computer.

PfcAJ · Mar 5, 2013

Breaks to backgas before every gas switch and a 12mins on o2/ 6 off routine when at 20ft. I don't add any extra time when doing this, including on reasonably sporty dives. Also consider a low-ish bottom ppo2 in the 1.0-1.2 neighborhood.

Gas breaks are definitely about CNS. OTUs become an issue too on long exposures, but that doesn't have the same risk as having a seizure at depth.

On dives like that, it's a good idea to have someone on the surface for support, and I'd consider some in water help to take tanks and give you some more options if things go tits up.

Doppler · Mar 5, 2013

Just to stoke the fire...

Air Breaks? what are they, and do people take them for the wrong reason? | Doppler's Tech Diving Blog

PfcAJ · Mar 5, 2013

Steve, I've read your article before, and it always leaves me with the same question; If gas breaks don't affect the CNS o2 'clock', how can we explain people going WELL over the 'limit' time and time again by employing gas break strategies? I'd be long gone if 100% (heck, even 300%) equaled a toxic event.

If the model doesn't match reality, then the model is wrong

I do agree that a component of the gas break is to maintain deco efficiency, which is why I don't count my off-oxygen time as additional deco time.

The one thing I think we all can agree on is that the entire thing is poorly understood and deserves a lot of respect.

Tigerman · Mar 5, 2013

Doppler:
Just to stoke the fire...

Air Breaks? what are they, and do people take them for the wrong reason? | Doppler's Tech Diving Blog

If you wanna stoke the fire, just turn on the 100% o2?

Air Breaks and CNS

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