ppO2 for nitrox, why so low?

[rjack321]

"Most"
People do tox at 1.6, especially when combined with exercise and CO2. They almost always lose their regulator and drown. In the military a 0.1% death rate might be considered mission acceptable risk. Recreationally its not ok to have 1/1000 divers die. So the recreational limits are set at 1.4, where virtually no one convulses (but it has still happened just exceptionally rare)

You dont really get that much NDL value out of a small amount of extra O2. If you want to stay longer you can do staged deco

 

[KenGordon]

That 3-6 hoursvat 2.0 ppo2 is talking about pulmonary oxygen toxicity. Later in the article is says this -

“In general, people can tolerate more oxygen in a dry chamber than in the water. In fact, most divers can tolerate two hours of oxygen at 3.0 ATA (66 fsw or 20 msw) in a chamber with few difficulties. While exercising in the water however, several divers have had convulsions at pO2s as low as 1.6 ATA. ”

And elsewhere why that maters for Nitrox diving.

 

[GJC]

diverite.com, the article is for divers but id guess the data is from hyperbaric treatment studies

Oxygen Toxicity - Signs and Symptoms | Dive Rite

The graph has no citation for where it came from and the article does not describe the criteria used to create the cutoff line. I suspect it's from quite some time in the past and may have been created as a guide for hyperbaric therapy.

The article says a number of people get cns tox at 1.6

 

[Bowers]

after reading over it again (and the quotes here), i see where i skimmed too quickly over the in the water as compared to dry chamber. Thank you all for the imputs!

 

[rongoodman]

btw what does YMMV mean?

Your mileage may vary.

 

[caruso]

If we are talking nondecompression single tank diving on Nitrox that is under 40% then yes, the 1.6 limit is ultra conservative. I have never heard of a single documented case of an 02 toxicity hit on such a diver under those circumstances.

I too use P02 of 1.6 and if I could I'd set it higher.

 

[Landlocked123]

1.4 on mine and no higher.

 

[oldschoolto]

You can and I will dive 2.0 but no hard work.. just slow moving and no trying to remove a brass porthole ... I feel going up to 1.8 is a good number for most dives.. ymmv...

Jim..

 

[KevinNM]

I’ve read a report of someone drowning after CNS toxicity hit at 1.3 ata, but no real details other that it was a highly fit female cave diver.

Don’t screw around with CNS oxygen toxicity limits. Pulmonary toxicity is a lot more forgiving, but a CNS hit is not usually survivable.

 

[Gareth J]

I’ve read a report of someone drowning after CNS toxicity hit at 1.3 ata, but no real details other that it was a highly fit female cave diver.

Don’t screw around with CNS oxygen toxicity limits. Pulmonary toxicity is a lot more forgiving, but a CNS hit is not usually survivable.

I think Kevin puts it very well, don't screw with CNC toxicity limits, they are not forgiving.

While it is some time since I looked at this in any depth. The most relevant point is that the body reacts significantly different in a dry environment compared with an immersed environment.

A number of the graphs I have seen in the past have been medical information, rather than specifically diving. Which don't account for the different ways the body reacts to a wet/dry environments.

Another point to remember, is a fitting diver in a chamber during treatment is manageable. A fitting diver in water has a very high risk of turning into a fatality!