CNS not important anymore?

[Agro]

An experienced diver told me CNS has "no importance" anymore. You may make a dive which brings you out of water at 100 or 200 or 500% or whatever CNS. It simply does not matter anymore. Never heard about that, did you?

 

[rjack321]

An experienced diver told me CNS has "no importance" anymore. You may make a dive which brings you out water at 100 or 200 or 500% or whatever CNS. It simply does not matter anymore. Never heard about that, did you?

There are certainly plenty of folks exiting the water with over 100% CNS which is only 45mins of cumulative O2 time afterall, nevermind the CNS accumulated on the bottom and on other deco gases. Shrugs, does it matter sure, is the clock accurate? not at all

 

[Agro]

There are certainly plenty of folks exiting the water with over 100% CNS which is only 45mins of cumulative O2 time afterall, nevermind the CNS accumulated on the bottom and on other deco gases. Shrugs, does it matter sure, is the clock accurate? not at all

Does it matter? Sure.

Is the clock accurate? Not at all.

So does CNS% exist or does it not? Is 100% OK? Or 200%? Or 1'000%?

I do know lots of divers came out of water with 400%. Was this a calculated risk or no risk at all?

Does it have importance or not? That's the question.

 

[rjack321]

well people still tox and precisely why will probably never be known

 

[Underwater Tourist]

An experienced diver told me CNS has "no importance" anymore. You may make a dive which brings you out of water at 100 or 200 or 500% or whatever CNS. It simply does not matter anymore. Never heard about that, did you?

This might be of interest:

Thread 'Thread split: CNS toxicity limits'

Sep 3, 2023

It was explicitly part of my crossover in May 2018, including adding the shutoff to the stock MAV and "breathing down" a higher ppO2 (e.g like 1.35 down to 1.2).

No disrespect meant to yourself @rjack321, but I am simply stunned that folks would think (or now think / are taught) that 1.35 is a 'relatively high' po2, CCR or otherwise, unless one was doing very extensive long duration dives.

• Kay Dee
• Replies: 71
• Forum: Rebreather Diving

• 

 

[nadwidny]

So does CNS% exist or does it not? Is 100% OK? Or 200%? Or 1'000%?

Does it have importance or not? That's the question.

It has no relevance in the real world.

 

[Agro]

This might be of interest:

Thread 'Thread split: CNS toxicity limits'

Sep 3, 2023

It was explicitly part of my crossover in May 2018, including adding the shutoff to the stock MAV and "breathing down" a higher ppO2 (e.g like 1.35 down to 1.2).

No disrespect meant to yourself @rjack321, but I am simply stunned that folks would think (or now think / are taught) that 1.35 is a 'relatively high' po2, CCR or otherwise, unless one was doing very extensive long duration dives.

• Kay Dee
• Replies: 71
• Forum: Rebreather Diving

• 

This leeds to even more questions than answers. Most of the statments contain "it seems" or similar.

Is there no scientific approach to this topic? NOAA limits were fixed may years ago and they still seem to exist. Is it really in theory only?

 

[Agro]

It has no relevance in the real world.

Who sais so?

 

[JMarc]

This leeds to even more questions than answers. Most of the statments contain "it seems" or similar.

Is there no scientific approach to this topic? NOAA limits were fixed may years ago and they still seem to exist. Is it really in theory only?

Paul Bert effect is real.

Threshold is variable depending on pressure, time and other factors, including individual variability, stress, physical effort,... Being under water, you get it more quickly than in a dry hyperbaric chamber.

NOA limits are empirical and are probably quite conservative. Not a bad thing considering that consequence while under water is often fatal if you aren't wearing a Full Face Mask, but there are lot of anecdotes of divers pushing past them.

I'm not aware of tentatives to determine more precise limits. Considering the risks, trying to do so would probably need better justification to get a pass from the ethical committee than just "rec and tech divers would like to have them" and that's after you've the funding.

 

[crofrog]

It's interesting to look at the navy tables...

They do O2 at 30ft, and the CNS %s will be high...

Here is a dive to 90ft on air with the O2 deco schedule from the USN rev7