Myth or not? Deep air/oxtox

[gcbryan]

I've read that in days past when deep air diving was more prevalent that very few divers actually experienced oxtox. Supposedly exceeding EAN MOD's has resulted in more hits.

Is this true?

The logic (truth or myth?) is that using air at oxtox depths resulted in such high nitrogen levels that the resulting narcosis somehow delayed the oxtox onset. When EAN MOD's were exceeded the nitrogen levels were lower and weren't enough to offset oxtox symptoms.

Is there or was there ever any truth to this?

 

[Darin]

Wow, good question.

But I'm left with the question in the back of my mind, "Why?" There are some other alternatives that I think are better than risking it.

I hope someone has an answer, I'd like to know as well!

Darin

 

[H2Andy]

more than likely the truth is that the "dangerous" depth for air is much deeper than the "dangerous" depth for nitrox, so fewer divers were diving to those depths, so fewer divers were getting hit with oxtox

i haven't seen anything that suggests that narcosis is an alleviator of oxtox

 

[DandyDon]

Actually, I have never seen any confirmed case of OxTox described with specifics....?

 

[gcbryan]

I've never personally read of a case of oxtox in a diver using air but I haven't really looked very hard either.

 

[Charlie99]

i haven't seen anything that suggests that narcosis is an alleviator of oxtox

I have seen some anectdotal reports that suggest such. And adding a bit of N2 into a mix for very deep dives has been shown to reduce HPNS, another nervous system problem, so it wouldn't surprise me if high ppN2 tends to make CNS oxtox less likely.

IMO, it's kind of a like mixing some downers (N2) and some uppers and seeing what ya get. A very risky business.

 

[Charlie99]

Actually, I have never seen any confirmed case of OxTox described with specifics....?

I've seen a few. I'll add links if I can find them, but the ones that I recall include things like

breathing a deco bottle while on the bottom.

Toxing while on 100% at 20' or so. Somewhere I've seen a report of this happening to a diver at the Andra Doria.

Oxtox incident in a GUE Tech 1 class due to backgas not being analyzyed. There was a very detailed report from AG posted by MHK on rec.scuba. IIRC, what should have been a low FO2 backgas was a 50% O2 mix, and oxtox was after something like 20 minutes at 2.3ata ppO2.

 

[TSandM]

Well, I went and puttered about in the Rubicon Foundation's research archive, and to my surprise, the papers I found (although they were work done in rats) suggest that increasing inert gas concentration -- regardless of what inert gas it is -- INCREASES susceptibility to oxygen toxicity, at least measured by time to seeing abnormal electrical activity in the brain, up to a certain point, and beyond that, the susceptibility returns to what it is on pure O2.

I have read the suggestion before that high ppN2s might be protective, but I didn't find anything there to support that.

 

[Rick Inman]

Don't ya just love it. We're all just a bunch of diving lab rats...

 

[ianr33]

I've read that in days past when deep air diving was more prevalent that very few divers actually experienced oxtox. Supposedly exceeding EAN MOD's has resulted in more hits.

Is this true?

The logic (truth or myth?) is that using air at oxtox depths resulted in such high nitrogen levels that the resulting narcosis somehow delayed the oxtox onset. When EAN MOD's were exceeded the nitrogen levels were lower and weren't enough to offset oxtox symptoms.

Is there or was there ever any truth to this?

I certainly believe this to be true.(Although I have no intention of finding out !)
It is not so much the narcotic affect of nitrogen so much as its sedating affect (which might be the same thing)
There was a very moving thread on The DecoStop recently where a young lady died,apparently due to oxygen toxicity http://thedecostop.com/forums/showthread.php?t=26017
She was diving a PO2 of 1.4,which she had done many times on nitrox,but on her last dive was diving trimix. The supposition was that she was unususally susceptible to oxygen but this had always been masked in the past the nitrogen.