O2 toxicity liklihood below pp 1.4

[boulderjohn]

That is the exact opposite of what I have experienced in the commercial diving arena. We routinely ran O2 at 1.8 to 2.0 ATA in the water (umbilical for gas & communications to a hat or FFM) and 2.8 in the chamber. I have never seen or spoken with a diving supervisor who had a confirmed OxTox hit on the job. However, divers O2 levels were quickly reduced at the least hint of a symptom — switch gases and tell the diver to purge their umbilical or just remove the O2 mask in the chamber.

So tell me how that works with an open circuit diver feeling the symptoms at 150 feet.

 

[dumpsterDiver]

So tell me how that works with an open circuit diver feeling the symptoms at 150 feet.

Switch to the pony filled with air and hit the up button?

 

[boulderjohn]

Switch to the pony filled with air and hit the up button?

Oddly enough, just such a situation happened last summer.

In February I buddied with a diver, a physician, whose best friend had had a CNS event at 150 feet last summer. The diver had filled his tanks in preparation for a dive some time before, and then suffered an injury that kept him out of scuba for a while. When he was ready to return, he joined a deep air dive, using the tanks he had filled months before. He remembered putting air in them, but his memory was faulty. It was EANx 36, which is not a good thing to be breathing at 150 feet. The best guess is that he did feel one of the VENTID symptoms and realized what was happening, because he did hit the up button.

The official cause of death was apparently an embolism.

 

[Akimbo]

So tell me how that works with an open circuit diver feeling the symptoms at 150 feet.

Switch to the pony filled with air and hit the up button?

Yep, or even just go up. OxTox symptoms subside very rapidly on the few hits I have read about. Around half the time these commercial divers reported their suspicion of symptoms to the supervisors.

Diver awareness is critical and many times greater on Scuba — open or closed circuit. Leave bottom and/or go to a lean mix when in doubt. Always have a leaner mix to use on multi-gas decompression schedules and contingency tables to back them up… assuming survival is part of your dive plan.

 

[dumpsterDiver]

Oddly enough, just such a situation happened last summer.

In February I buddied with a diver, a physician, whose best friend had had a CNS event at 150 feet last summer. The diver had filled his tanks in preparation for a dive some time before, and then suffered an injury that kept him out of scuba for a while. When he was ready to return, he joined a deep air dive, using the tanks he had filled months before. He remembered putting air in them, but his memory was faulty. It was EANx 36, which is not a good thing to be breathing at 150 feet. The best guess is that he did feel one of the VENTID symptoms and realized what was happening, because he did hit the up button.

The official cause of death was apparently an embolism.

so he switched to an air filled pony or not? There was a local instructor who died last summer from an O2 hit I think it was...

 

[boulderjohn]

so he switched to an air filled pony or not? There was a local instructor who died last summer from an O2 hit I think it was...

No--I suspect we are talking about the same guy.

 

[Duke Dive Medicine]

Re-stating for emphasis:

Carbon dioxide is a vasodilator and may lower your ox-tox threshold by increasing perfusion of neural tissues.

Arterial pCO2 increases with exertion, depth/gas density, and external breathing resistance, and increased paCO2 definitely increases the risk for CNS O2 toxicity.

Predictors of increased PaCO2 during immersed... [J Appl Physiol. 2009] - PubMed - NCBI
CNS oxygen toxicity in closed-circui... [Aviat Space Environ Med. 2006] - PubMed - NCBI

 

[IWantToBeAFish]

Thanks for the information everyone. A few good papers to read there. Could you go as far as to say that within recreational 40m, single tank, air-only diving that an ox-tox hit was almost impossible?

I suppose I'm wondering whether the omission of ox tox mention from the non-nitrox training literature is completely justified or whether it is still something to be aware of, albeit extreme under conditions? It would the addition of such just frighten people unnecessarily?

Thanks.
Adam

 

[boulderjohn]

Thanks for the information everyone. A few good papers to read there. Could you go as far as to say that within recreational 40m, single tank, air-only diving that an ox-tox hit was almost impossible?

It all depends upon the size of the single tank. Guessing what you meant, though, I would say you are very close to accurate.

If you are talking about an AL 80 tank, I will venture to say it is highly unlikely for any blend of recreational nitrox as well.

 

[Duke Dive Medicine]

Thanks for the information everyone. A few good papers to read there. Could you go as far as to say that within recreational 40m, single tank, air-only diving that an ox-tox hit was almost impossible?

I suppose I'm wondering whether the omission of ox tox mention from the non-nitrox training literature is completely justified or whether it is still something to be aware of, albeit extreme under conditions? It would the addition of such just frighten people unnecessarily?

Thanks.
Adam

Adam,

The extreme conditions you're talking about would be beyond the training of a recreational air diver. The pO2 in compressed air doesn't even get to 1.0 until 124 feet, and CNS oxygen toxicity is not an issue below 1 ATA. I think it's very reasonable that it's not mentioned at that level of training.

Best regards,
DDM