Nitrox Question

[PfcAJ]

So many diver deaths are called "drowning" or "medical issue" that its almost impossible to know the real cause. Why walk the razor's edge?

The CNS % thing is BS, imo. It doesn't work at the low end (people have can symptoms way below 100%) and it doesn't work at the high end (people can have way above 100% and not have symptoms). The data on it is so sketchy, to say "well, according to the NOAA table, you have 45mins at 1.6, so everything is great" it optimistic at best.

 

[diverdoug1]

Van Isle, I was one of the physicians at the 2000 DAN workshop, and what you say is correct BUT that perfect record no longer stands. I have also had patients seize at less than 1.6 ppO2 in the chamber. I would agree that the relative risk of diving a profile that exposes a subject to a ppO2 of 1.6 is low. Having said this, I still think that said risk is high enough to warrant reevaluation of 1.6 ppO2 as an acceptable recreational diving limit of Maximum ppO2. I also think that the last couple of posters are mixing apples and oranges. We are talking about oxygen induced seizures and maximum operating depths, not accumulated oxygen toxicity units.

 

[TSandM]

Well, what it comes down to is this: The benefit of pushing a richer mix into deeper depths is to try to cadge a little more bottom time from the decompression gods. The risk is drowning.

I'll go with Mike Ferrara, and say that such dives should be planned and executed as proper staged decompression dives, using mixes which are appropriate for the depth, and doing the decompression penalty you incur.

 

[Puffer Fish]

Van Isle, I was one of the physicians at the 2000 DAN workshop, and what you say is correct BUT that perfect record no longer stands. I have also had patients seize at less than 1.6 ppO2 in the chamber. I would agree that the relative risk of diving a profile that exposes a subject to a ppO2 of 1.6 is low. Having said this, I still think that said risk is high enough to warrant reevaluation of 1.6 ppO2 as an acceptable recreational diving limit of Maximum ppO2. I also think that the last couple of posters are mixing apples and oranges. We are talking about oxygen induced seizures and maximum operating depths, not accumulated oxygen toxicity units.

Doug, thanks for posting.

The confusion between the two would seem to be understandable. Do you happen to know if longer exposure to high O2 increases your chances... or your chance stays constant, just that you are exposed longer?

Not sure that made any sense...put another way.. does your chance of having an event remain constant...with the only risk factor being more time.. or does the risk increase at a faster rate than just time?

I would assume that anyone in a chamber would most likely have a pretty high accumulation level (that may be wrong)...so is this compounded from that or independent?

 

[diverdoug1]

Puffer, it would seem to make sense that a longer time exposed to the high ppO2 would increase the risk of seizure BECAUSE divers that have had oxygen tension induced seizures don't always seize immediately upon exposure.
In response to your question about chamber personel, when in the chamber they are breathing the ambient air, not O2 through a mask.

 

[Puffer Fish]

It would be nice if, when one makes an educated choice regarding O2 exposure that we knew more than we did...

It may be that 1.6 at 80 and 1.6 at 120 ft are actually not exactly the same thing, but we don't seem to really know.

Given that we don't, one would seem to be advised to error on the side of caution.

 

[ianr33]

It may be that 1.6 at 80 and 1.6 at 120 ft are actually not exactly the same thing, but we don't seem to really know.

They are not quite the same thing. Gas is denser at 120 ,harder to remove CO2 so more chance of it building up. High CO2 and high O2 is a bad combination.

I would have no problem bouncing to 130 on 32% nitrox in good conditions,though I would certainly not plan a dive that way.

Swimming hard into a current at 218 feet on air (also1.6) would be a real bad idea due to CO2 buildup. (not to mention the narcosis)