If you had to choose, 80% or 100% for deco gas and why.

[victorzamora]

I think the biggest issue is the differing views of how to treat OxTox. AJ isn't alone in his distrust of single-dive CNS Clock exposure limits....even if it seems so in this thread. There have been tons of dives performed exceeding the thousands of percent with no ill effect, and rarely has a single dive in the thousands of percent resulted in big issues. What has messed people up MUCH more frequently is oxygen buildup over multiple dives.....even if they consistently stay well under the CNS clock limits.

To everyone talking about B6 Vitamins and drunk driving: I don't think those are good analogies. I think the better analogy would be deco profiles. We all know that deco is a "science" (art) and that nobody actually really knows what's going on. Does this sound like CNS? It should. Deco algorithms are methods by which we can guess at how safe we'll be on a given dive. Their purpose is to keep us from getting bent, right?

Well, let's plan a dive that's "supposed" to get us bent to pieces. We'll say that that dive is like exceeding a single-dive CNS limit. If getting out of the water safely was common diving that profile, we would say that profile was inaccurate. Now, let's plan a long series of repetitive dives using the same algorithm. Despite staying within the planned limits, people are getting hit frequently. We would also say that algorithm was inaccurate. Saying that the algorithm used sucks is NOT the same as saying you don't believe in the chance of getting bent.....just that the paradigm under which you believe to understand that phenomenon is inaccurate.

I think this is what AJ is expressing, and it's a concern I've heard from a lot of highly trained divers and instructors. Accepting the something as gospel is part of what keeps further study from being accomplished properly.

 

[lowviz]

... What has messed people up MUCH more frequently is oxygen buildup over multiple dives.....even if they consistently stay well under the CNS clock limits. ...

I share this concern as it seems to be poorly tracked. There is evidence that long term exposure (whole body, lung irritation) also sensitizes one for a short-term high concentration hit. Yes, more work needs to be done.

 

[PfcAJ]

Lol this is nothing like vitamins.

 

[danvolker]

Lol this is nothing like vitamins.

Not to mention that 100% of an RDA is one of the most useless suggestions that has ever been created---with virtually no value in Nutritional planning. Optimal health typically requires vitamin levels 20 to 100 times the RDA for many vitamins or minerals....meaning you need to do your own research on many things that come from supposed "authorities"...certainly for an agency like the FDA that is really there to protect the Pharmeceutical Industry money, and routinely ignores what is good for the individual.....

 

[kr2y5]

But its not 100% of anything that's real.

How do you define "real"?

With BAC you can quite easily turn it into a "risk of accident" or describe symptoms at different BAC levels. With this % thing, you can't do any of that.

My understanding is that the exposure limits are based on data from experiments, in which people have experienced symptoms, such as this one, and probably others... that seems to contradict what you just stated.

My gripe is that its presented as a percentage of something.

Every number can be presented as a percentage of something... it's just a different unit, like going from pounds to kilograms. For example, if an average male is 6 feet tall and weights 200 lbs, I am about 100% tall and 97% heavy compared to an average male. This does not necessarily mean I will break in half if I grow an inch longer, or spontaneously implode under my own weight if I gain a few more pounds. I think that perhaps % of a limit in the case of CNS clock might be easier to rememember and keep track of than the raw number that represents cumulative exposure.

That "something" isn't meaningful. It doesn't help divers decide the risk they're taking on a dive, and being within "100%" doesn't always = safety.

A lot of phenomena in nature don't exhibit this sort of discrete transition, driving after drinking was one example. There is nothing magic as you exceed the limit, no singularity, just getting past some commonly used threshold of risk based on some limited past experiments. The same happens with NDL, no? Should one assume that the gradient factors are % of something meaningless as well, because I fail to see much of a difference between those, and the CNS clock, with respect to the way they are defined.

Future studies will probably revise the limits, but to say that it is not useful demands an explanation. How do you define "useful", and do you have any data to back this claim?

 

[PfcAJ]

How do you define "real"?



My understanding is that the exposure limits are based on data from experiments, in which people have experienced symptoms, such as this one, and probably others... that seems to contradict what you just stated.



Every number can be presented as a percentage of something... it's just a different unit, like going from pounds to kilograms. For example, if an average male is 6 feet tall and weights 200 lbs, I am about 100% tall and 97% heavy compared to an average male. This does not necessarily mean I will break in half if I grow an inch longer, or spontaneously implode under my own weight if I gain a few more pounds. I think that perhaps % of a limit in the case of CNS clock might be easier to rememember and keep track of than the raw number that represents cumulative exposure.



A lot of phenomena in nature don't exhibit this sort of discrete transition, driving after drinking was one example. There is nothing magic as you exceed the limit, no singularity, just getting past some commonly used threshold of risk based on some limited past experiments. The same happens with NDL, no? Should one assume that the gradient factors are % of something meaningless as well, because I fail to see much of a difference between those, and the CNS clock, with respect to the way they are defined.

Future studies will probably revise the limits, but to say that it is not useful demands an explanation. How do you define "useful", and do you have any data to back this claim?

Its not useful because you can tox without surpassing 100% and you can surpass 100% and not tox. So of what use is this "percentage" if its not predictive at all? This is the one thing no one can answer. If the purpose of tracking CNS% is to keep you safe by not surpassing "100%", how can you have ANY trust in it if people tox before 100% is reached? Similarly, if 100% does not equal a toxic event (hell, even 5000% doesn't equal a toxic event), of what use is tracking it?

I think this is the main thing that's being lost of some of you guys. The CNS Clock is NOT useful for describing your risk of an oxygen toxicity event.

Its a little funny how much folk cling to this concept despite numerous cases of it not holding water.

 

[LiteHedded]

Its not useful because you can tox without surpassing 100% and you can surpass 100% and not tox. So of what use is this "percentage" if its not predictive at all? This is the one thing no one can answer. If the purpose of tracking CNS% is to keep you safe by not surpassing "100%", how can you have ANY trust in it if people tox before 100% is reached? Similarly, if 100% does not equal a toxic event (hell, even 5000% doesn't equal a toxic event), of what use is tracking it?

I think this is the main thing that's being lost of some of you guys. The CNS Clock is NOT useful for describing your risk of an oxygen toxicity event.

Its a little funny how much folk cling to this concept despite numerous cases of it not holding water.

you were closer to 7000% than 5000.

wait that can't be right. you're not dead...

 

[PfcAJ]

Note to everyone:

Surpassing the "limits" is kind of uncharted territory. You might get it wrong and drown. Don't do it.

 

[kr2y5]

Its not useful because you can tox without surpassing 100% and you can surpass 100% and not tox. So of what use is this "percentage" if its not predictive at all? This is the one thing no one can answer. If the purpose of tracking CNS% is to keep you safe by not surpassing "100%", how can you have ANY trust in it if people tox before 100% is reached? Similarly, if 100% does not equal a toxic event (hell, even 5000% doesn't equal a toxic event), of what use is tracking it?

I think this is the main thing that's being lost of some of you guys. The CNS Clock is NOT useful for describing your risk of an oxygen toxicity event.

Its a little funny how much folk cling to this concept despite numerous cases of it not holding water.

Your definition of "predictive", requiring that you never tox before exceeding 100%, and always tox after exceeding 100%, seems absurdly restrictive... in the sense you propose to use the term "predictive", almost nothing in life is predictive, but that's hardly a commonly accepted meaning of the term. What you are referring to would better be described using the term "deterministic". I do not think anybody here claims that reaching 100% of the CNS clock deterministically, inevitably leads to immediate convulsions.

 

[PfcAJ]

Hence my argument that it's a poor tool. It doesn't work on the low end or the high end. The failure of it working on the low end is the biggest issue, I think. People can think they're in the clear because its "less than 100%", but they aren't.