EAN32 diver below you at 40-odd meters?

[PfcAJ]

http://www.rubicon-foundation.org:8080/dspace/bitstream/123456789/3991/1/15233161.pdf

Page 5 (67) has a little chart labeled "Day to day variations in time duration until onset of CNS oxygen toxicity symptoms of a single diver. From Donald, 1947 (16)." Interesting (and a little scary) to say the least.

This paper is a good overview of oxygen toxicity and the sources can take you deeper into the research.

 

[Slamfire]

(I know where I have the table from the papers on this, and if I have time, I'll find it.)

I'd appreciate it if you would. I'm not trying to be argumentative nor am I looking to pick a fight, but I've heard this before and never came across the evidence. I find it hard to take anecdotal references and place them above formally established guidelines by a serious, well-recognized organization. Maybe I should also start digging on how the NOAA table was developed, for that matter.

 

[Rainer]

<snip>

If you're interested in doing some reading, I'd suggest the following:

Oxygen and the Diver K. Donald (must read)

Oxygen Poisoning in Man K. Donald (ditto)

Rubicon Research Repository: Item 123456789/4855

Rubicon Research Repository: Item 123456789/3991

Modeling pulmonary and CNS O2 toxicity and estimation of parameters for humans -- Arieli et al. 92 (1): 248 -- Journal of Applied Physiology

For the story about Halbach (toxed at 1.4): The Deco Stop

Some nice "summary" threads:

The Deco Stop

http://www.scubaboard.com/forums/258723-post31.html

The Deco Stop

 

[NAM001]

OK, so:

You're diving EAN32 on a vertical wall with great viz. Everyone else is also diving EAN32. You see a diver (also diving EAN32 -- it's clearly marked on his cylinder) dropping deeper and deeper, faster and faster ... until you're at about 32 m (that's 105 fsw; near your MOD) and he's at least 10 m below you (138 fsw) and going deeper quickly.

What do you do?

I chose to exceed my MOD and swim down fast, grab him and tap him on the shoulder, and point to the depth on his gauge. He adjusted his buoyancy and then we both ascended quickly to above our MOD; no problem. But by the time I got down there and tapped him on the shoulder, we were at about 45 msw (148 fsw) or deeper. That's a PP02 of > 1.6; a CNS 02-tox risk.

Divers learn in our rescue courses not to put ourselves at too much risk when trying to rescue others -- 2 deaths are worse than 1; 2 lost or injured divers divide the rescue resources in half; etc. etc. But I still think I made the right choice. Countless divers have exceeded PP02s of >1.6 on air and EAN32 for short periods of time and had no problems, whereas a diver who's narced and keeps plummeting down a wall to 55 m or 65 m or deeper on nitrox is at a great degree of risk.

I'm receptive to those who can explain persuasively why I made the wrong choice, as well as those who can persuasively back me up. I think there's more to it than just PP02 because divers on air and EANx seem to tolerate greater PP02s than divers on trimix (in theory because the narcotic effect of N2 counteracts the neuroexcitatory effect of 02 toxicity, but helium doesn't). Any empirical data on what % of divers tend to tox at what depth, on what gas mix?





P.S. As I learned later, he's a scuba instructor qualified to teach nitrox courses. :depressed:

i cant tell you the numbers you ask for however i firmly believe you did the right thing. worse case you would get him from behind and bring him up to above 100. or get him on top of the wall. bravo ..... you can only hope that someone would do the same for you if needed.

 

[peterbj7]

I watched a friend, a highly experienced Red Sea dive guide who was using EANx 36, drop to around 50 mtr to recover two idiots who had chosen to ignore the dive briefing about a down current. She got away with it (the two idiots had just had their last dive of their holiday).

I've dived to a pO2 of 2.7 in warm water without incident. A friend has several times dived to 109 mtr on air in bitterly cold water (Dorothea Quarry in North Wales) and lived to tell the tale. Oxtox truly is unpredictable.

 

[lamont]

Um, you had a diver tox and die at 1.4 in FL last year... (there have been other deaths at 1.4).

On a long enough timeline with enough divers, someone will convulse and die with a ppO2 of 0.21 and then what do you do?

 

[NAM001]

i have read a lot of guff about this in many threads. perhaps i am wrong but i read limits as the "in normal conditions" situations. this is not a normal sitiation. this is an emergency
the short duration at the higher ppo's should not be considered in a save a life situation as a lind drawn in the stand and written in stone because of blind trust and lack of understanding. one day the gospel will be 1.2 and there will be those who will say we will all die if we hit 1.3 .....
teh physics doesnt change only the inbread fear of the unknown.

when i took my first class the levels were ppo 3.0 death, 2.0 onset of ox tox or anoxia as used. dont push 1.8 because you may be one of those who is more sensitive to o2.
ppo of 1.8 went to 1.6 went to 1.4.

at what level will divers completely ignore levels all together.
how long will it be untill a realistic level in some other area be ignored as being assumed to be over conservitive as is the ever lowering ppo's and then hurt someone.

ie so my puter says deco, no biggy it surely has been programmed to be over precautions so i probably really have an extra 10 minutes.

30 ft ascent rate heck use to be 60 so surely 90 is safe.

 

[dumpsterDiver]

i cant tell you the numbers you ask for however i firmly believe you did the right thing. worse case you would get him from behind and bring him up to above 100. or get him on top of the wall. bravo ..... you can only hope that someone would do the same for you if needed.

Worst case is you tox out and die?

 

[Rainer]

Sure, maybe, but can you cite a single documented death at 1.2 or 1.3 as of yet? It's ALL just a risk tolerance game. If notching slightly lower on the PPO2 scale gets me back to a zone with ZERO known fatalities at the cost of just a few minutes of extra deco, I'm willing to play (for bigger dives).

On a long enough timeline with enough divers, someone will convulse and die with a ppO2 of 0.21 and then what do you do?

 

[lamont]

Sure, maybe, but can you cite a single documented death at 1.2 or 1.3 as of yet? It's ALL just a risk tolerance game. If notching slightly lower on the PPO2 scale gets me back to a zone with ZERO known fatalities at the cost of just a few minutes of extra deco, I'm willing to play (for bigger dives).

Thing is that you're assuming that the convulsions at 1.4 were primarily caused by O2 tox.

Once you hit a convulsion at 0.21 ppO2 then you're quite certain that the convulsion had nothing to do with O2 tox and was just an underlying undiagnosed seizure disorder.

At 0.22 you can be pretty damn certain O2 tox wasn't the culprit, same with 0.23, 0.24, etc. At some point it starts to fuzzily become more likely that O2 tox either was the cause or a contributing factor, but there's always going to be a non-zero chance at any ppO2 of seeing the symptoms of a convulsion. At what point does the incidence of convulsions become low enough that its like worrying about a billion other low-risk things that we do every day that might kill us? Absolute zero risk isn't possible.