Dsix36

OK, I am planning a rather big dive and am looking to be in the water for 6 hours or more. About 4 hours of this will be deco. I am wondering what others have been doing to manage high CNS with similar dives?

Please only respond if you have actually done a 6 hour dive with significant deco.

CaveDive1

Does a chamber count? 5 minute air break for every 20 minutes of pure O2

Dsix36

Details of a chamber ride won't work for me. Having an O2 seizure in the chamber won't cause you to drown.

CaveDive1

You're probably right, but the O2 procedures are the same. 30 minutes on, 5 minutes off. Unless wearing a helmet is also an issue.

I/We changed it to 20/5 because I was paranoid. Doubt it really mattered.

Hagberg

Keep PO2 low during the working/bottom phase of the dive, and then take low-PO2 breaks while on Oxygen during deco. Doing 12 minutes on Oxygen and breaking for 6 minutes seems to enable you to stay alive for a very long time. For the limited deco you are looking at you might get away with doing 15 on, 5 off as well. (Easier numbers than 12 and 6) Keeping Helium content high may be beneficial in limiting CO2-buildup and perhaps also risk of tox.
Antioxidants before and during a dive has likely not hurt anyone either. I like Propel in a Camelback pouch for long dives. :)

wizbang

Dsix36 you don't mention what your current longest dive is (deco wise) and the CNS percentages you are experienced with and happy to tolerate.

If you are a strict 80% man then there will be a lot more "air" breaks if you have a tendency to hit the 100 odd mark then there will be less need for breaks.

With the deco being 4hrs of 6hrs I am imagining it not to be too deep.
If this is the case I would suggest managing the CNS and therefore the need for air breaks with a lower setpoint for bottom time.

Hope the info helps.
Wiz

Davydive

What about some fitness routine and preparation?
I am sure Kim and Peter can attest to that on their big Cayman dive.

Cheers!

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donlabbruzzo

Please be more specific with the details of the dive, MOD, Dil. Bottom time, deco time and run time.

As was already mentioned, long dives such as this require lower PPOS set points, typically 1.0 throughout the dive and possbily 1.2 to 1.3 for some portion of the 40' - 20' stops.

Depending on the MOD, it's unlikely you'll have Air to use during the "Air" breaks. if you're carrying 50% as a bailout gas, that's what you'll have to use for the breaks off 100%.

It's almost impossible to have a reasonable deco time without exceeding the OTU's during a six hour dive. Your CNS willl be manageable if your set points are kept low during the bottom portion of the dive.

I've made several 5 hour dives and exited the water far pasted the allowable OTU's. Not too much you can do.

Don

Lancer4545

Wear a FFM and you'll stand a much better chance of surviving a CNS event also...........

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jkaterenchuk

Don't forget to take into account hyperthermia and the effect a lower body core temperature might have upon the efficiency of your off gassing as well as its a bitch to be shivering for the last 90 minutes of deco.

John