Likelihood of getting oxygen toxicity at 1.4 PPO

[2airishuman]

Link to proceedings:

https://www.diversalertnetwork.org/files/Tech_Proceedings_Feb2010.pdf

Interesting stuff.

 

[JohnnyC]

Likely to tox at 1.4? Not very. It would seem as though there were other factors involved in the cases where a diver tox'd at 1.3 or 1.4.

Now, there are other reasons where you might want to limit your PO2 exposure, as an example I rarely dive higher than a 0.8 to a 1.0 in a cave, but those are typically exposures of many hours. It also saves my O2 clock so that I can spend more time at higher PO2's on deco where it is more efficient, and you are doing essentially nothing but breathing, mitigating some of the risks of higher PO2.

Doing an open water recreational dive, I would have absolutely zero qualms about diving a 1.4 and dipping down even higher. I also deco out at 6m at a 1.6 because 1) it's practical on a rebreather, and 2) it is marginally more efficient.

The agencies need some limit. 1.4 with a 1.6 contingency is a reasonable limit to hold divers to who don't have the experience or knowledge to utilize with higher PO2's properly, especially since the diving they are doing really doesn't require that level of understanding.

 

[J_Rod]

My .02.....If PADI and other international certifying agencies use a PO2 of 1.4 with a contingency of 1.6 max as their limits, and claim this is safe for recreational diving, then the conservatism is already built into their guidelines. Certainly there may be extenuating circumstances such as physical condition, medications/drugs, and exertion that may affect this (which we are also taught, but is the obvious caveat to reduce their liability) . Since ystrout has less than 50 dives, I'm assuming deco stops are not in his dive plans, other than a standard safety stop...and besides.........What Wookie said......

 

[BertStevens]

I once had to take a chamber ride for some slight numbness in my hand. It was 60 feet on 100% O2. Of course I was flat on my back, resting and took 15 minute air breaks for every 30 minutes of 100% O2.

It was implied and I always thought OxTox was instant if you went above 1.6. But it’s more time and workload dependent.

 

[Wookie]

I once had to take a chamber ride for some slight numbness in my hand. It was 60 feet on 100% O2. Of course I was flat on my back, resting and took 15 minute air breaks for every 30 minutes of 100% O2.

It was implied and I always thought OxTox was instant if you went above 1.6. But it’s more time and workload dependent.

My wife suffers from PPO2 levels above about 1.8. The buzzing in her ears is very loud just before she passes out.

I OTOH, am happy at 2.0.

 

[Storker]

if 1.6 was "very" likely, then there would be a mountain of bent tech divers every time we do deco....

I seem to remember - maybe from my nitrox class, IDK - that the probability of toxing increases with physical activity. Last time I checked, there's a certain difference between the physical activity of a tech diver hanging in deco, and the physical activity of most divers during bottom time. I have no problems squaring "max 1.4 pPO2 during bottom time" with "max 1.6 pPO2 during deco"

we found several reasonably convincing cases occurring at 1.3 and 1.4.

The question is, of course, out of how many dives? Yes, I know. That's a question to which there is no answer due to insufficient data.

But I guess your point was that there's almost always a certain risk of toxing. The question is just how big that risk is and at which pPO2 that risk is acceptable - or negligible.

The key to 1.6 being safe for deco is that no work is being done. Personally I always use 1.2 at depth as my max PO2.

Thanks. You've just added another anecdote to support my assumptions.

 

[Lorenzoid]

Is it known what causes the inverse relationship between PP02 level tolerance and what we're referring to as "physical activity." Is it CO2 retention? Or something else, such as blood perfusion? Or a combination of factors?

 

[ystrout]

All, thanks for the replies. They were very interesting to read and informative.

Like Jrod said, I'm not doing deco. Just using nitrox to increase my bottom time for deeper/consecutive dives without long surface intervals and was curious to learn whether going past 1.4 or 1.6 would hit you like a rock, or whether that was just an estimate for safe diving like the recreational dive algorithms/tables.

 

[PfcAJ]

The thing with pushing po2 is the consequence of a toxic episode. Unlikely to survive, even though it is an unlikely event.

The consequence of a lower po2 is a slightly reduced dive time. Like a few minutes.

To me it’s not worth pushing it at all.

 

[Wookie]

The thing with pushing po2 is the consequence of a toxic episode. Unlikely to survive, even though it is an unlikely event.

The consequence of a lower po2 is a slightly reduced dive time. Like a few minutes.

To me it’s not worth pushing it at all.

But what do you consider pushing?