Thread split: CNS toxicity limits

[stuartv]

Regardless of where the data came from, it’s not a useful tool.

“100%” of the limit doesn’t really mean anything. Also, being below the limit doesn’t mean anything either. Passing 100% doesn’t mean anything. It doesn’t give you and information of value as to your risk of experiencing a CNS toxicity episode.

So, you just dive 100% O2 at all times, in all depths?

Have you ever had a CNS hit?

 

[PfcAJ]

So, you just dive 100% O2 at all times, in all depths?

Have you ever had a CNS hit?

Obviously I do not dive 100% oxygen at all times at all depth. It is known that high po2s are bad. What is not known with ANY certainty is the relationship between higher po2 and time. The NOAA CNS% attempts to quantify it but it does such a horrible job that the tool is useless.

Hitting 100% of the NOAA CNS exposure doesn’t mean you’re going to have a toxic event. We don’t even know what the probability of having an event is at that “limit”. So what’s it 100% of, exactly?

I’ve been at like 3500%. No toxic events ever. Over 30x the “limit”. So I guess the limit isn’t the limit? See how this is a bad tool?

Edit: removed an extra 0. Point still stands.

 

[stuartv]

Obviously I do not dive 100% oxygen at all times at all depth. It is known that high po2s are bad. What is not known with ANY certainty is the relationship between higher po2 and time. The NOAA CNS% attempts to quantify it but it does such a horrible job that the tool is useless.

Hitting 100% of the NOAA CNS exposure doesn’t mean you’re going to have a toxic event. We don’t even know what the probability of having an event is at that “limit”. So what’s it 100% of, exactly?

I’ve been at like 3500%. No toxic events ever. Over 300x the “limit”. So I guess the limit isn’t the limit? See how this is a bad tool?

You don't dive 100% and you (presumably) have not had a CNS hit.

So, how did you figure out what to do for your own exposure limits?

 

[PfcAJ]

You don't dive 100% and you (presumably) have not had a CNS hit.

So, how did you figure out what to do for your own exposure limits?

I dive 100% oxygen when it’s appropriate.

In absence of an even halfway decent tool for measuring and tracking exposure and risk, I simply don’t. I do know what works, evidenced by a ton of dives by a bunch of people: Low po2 (1.0-1.2) on the bottom, max 1.6 resting for deco, frequent breaks to a low po2 gas during deco.

My whole point here is to highlight that the NOAA CNS exposure limits are not a good tool and you can’t put too much (if any) stock in their accuracy or effectiveness.

 

[stuartv]

I dive 100% oxygen when it’s appropriate.

In absence of an even halfway decent tool for measuring and tracking exposure and risk, I simply don’t. I do know what works, evidenced by a ton of dives by a bunch of people: Low po2 (1.0-1.2) on the bottom, max 1.6 resting for deco, frequent breaks to a low po2 gas during deco.

My whole point here is to highlight that the NOAA CNS exposure limits are not a good tool and you can’t put too much (if any) stock in their accuracy or effectiveness.

I understand your point. That's why I'm trying to understand where you learned how to plan your own exposure limits.

It seems that you are saying you learned "what works" by asking a bunch of people who've done a ton of dives. So, where did they learn what works?

 

[PfcAJ]

I understand your point. That's why I'm trying to understand where you learned how to plan your own exposure limits.

It seems that you are saying you learned "what works" by asking a bunch of people who've done a ton of dives. So, where did they learn what works?

In the early days of tech diving, there was a lot of trial and error.

And you know how error goes when underwater.

The NOAA limits weren’t even published till the late 70s. The Navy had something similar in the early 70s. Tech guys had been (and continue to) push every limit and boundary out there.

 

[Underwater Tourist]

@PfcAJ how often do you take breaks to lower pO2 during deco and for how long?

 

[Capt Jim Wyatt]

The NOAA CNS% attempts to quantify it but it does such a horrible job that the tool is useless.

Please cite your reference to these data being useless.

 

[grantctobin]

Please cite your reference to these data being useless.

Do you think it is possible to cite a reference showing the data is useful? Anecdotally, I have not found it to be remotely accurate in predicting tox.

 

[PfcAJ]

Please cite your reference to these data being useless.

Just look at it with your eyes.

It is evident that 100% isn’t 100% of anything. If it was, you me and all our friends would be toast because we’ve all passed 100% many many times.