Oxygen toxicity studies

[Lastdive]

I am the “them” you are referencing. I do not think the NOAA tables reflect reality.

“100%” doesn’t mean anything as if been shown for decades now that people can repeatedly expose themselves to 10-30x (or more) of the “maximum” and not suffer ill effects. This calls into serious question the validity of the NOAA oxygen toxicity guidelines.

For these individuals that exceeded 10-30 times the maximum exposure, are they exceptions to the guidelines or an indication that the rule is bunk? Are the guidelines good for anyone? Are these guys just diving hundreds of times per year and have developed a tolerance to CNS toxicity?

Is Johnny Just-started-diving-yesterday going get a seizure for doubling 100%? What if he's a little thick around the middle and in bad shape? How does your general health play into breaking the rule? Have there been individuals that developed oxygen toxicity below 100%?

What should the guidelines be? Should they just be different for elite divers in your opinion? What is safe and what is pushing your luck?

 

[Capt Jim Wyatt]

I am the “them” you are referencing. I do not think the NOAA tables reflect reality.

I recall that U R the "THEM" now....haha. I tend to agree with your sentiment on this subject. Even though we have zero empirical evidence to support the hypothesis.

 

[PfcAJ]

For these individuals that exceeded 10-30 times the maximum exposure, are they exceptions to the guidelines or an indication that the rule is bunk? Are the guidelines good for anyone? Are these guys just diving hundreds of times per year and have developed a tolerance to CNS toxicity?

Is Johnny Just-started-diving-yesterday going get a seizure for doubling 100%? What if he's a little thick around the middle and in bad shape? How does your general health play into breaking the rule? Have there been individuals that developed oxygen toxicity below 100%?

What should the guidelines be? Should they just be different for elite divers in your opinion? What is safe and what is pushing your luck?

Lots of unknowns there. I don’t have those answers, but it’s clear that the current guidelines aren’t reflective of reality.

 

[nadwidny]

I've talked to Sawatzky and Pollock. Both say the CNS clock is a crock.

 

[rjack321]

What should the guidelines be? Should they just be different for elite divers in your opinion? What is safe and what is pushing your luck?

Let us know when you figure it out. Nobody knows and it's a difficult study to even ethically design. And more importantly generally not needed by the folks who might want to fund this work (the Navy and commercial companies use chambers for deco not in-water).

The NOAA CNS limits are reliably safe, but your dives will be constrained.

 

[Diver-Drex]

The NOAA guidelines were set up to keep risk very low. As the variability between divers is great, you’ll have a few that can’t tolerate the limits and some that can go way over with no problems. Then there is variability dive to dive. So yes, there will be exceptions but exceptions don’t invalidate the rule.

A great example is two hour 20’ dives on O2 rebreathers. This is a tactical dive profile. The CNS exposure is well off the charts but the divers all do fine. They are in excellent physical condition, the selection and training process eliminates individuals who can not tolerate it and the acceptable injury rate is far higher than is acceptable in recreational diving. The same is true with anything coming out of NEDU. Those individuals are exceptions to the rules and what they can and are willing to tolerate can not be applied to the general diving population.

 

[tursiops]

I have understood that those NOAA limits are not meant to be averages, or for special people, or for even average people, but rather they are provided in the spirit of the "minimums" for time-before flying; most will be OK using them, very few will need more time before flying. So when it says 45 mins for a max exposure time, you are on pretty solid ground. Individual variability may mean you get more time than that, but it is not like you will need less.
The big takeaway from the early work (see, for example, "Oxygen and the Diver" by Kenneth Donald) and discussed much in all the more recent work (see attachments for example), the individual-to-individual variability is huge, and the within-individual variability is also large.

 

[ofg-1]

Hi, is me, Them.

If you are "them", does that mean that you are not one of "us"?