Any reported cases of Ox Tox between 1.4 and 1.6?

[crofrog]

The logical conclusion you came to based on an "overall risk level" is extremely misguided.

Example:

Chance of death in car crash: Low - most car crashes are minor and don't involve significant injuries.
Chance of death in an airplane crash: High - airplanes tend to crash at high speed and kill everyone.

Conclusion: Traveling my Car is safer than by Plane.

Reality: Airplanes crashes are vanishingly rare, and car crashes kill ~10,000 times more people than airplane crashes each year.

Oxygen toxicity events in Scuba diving are vanishing rare. DCS occurs far more frequently resulting in hundreds or thousands of injuries every year. Even finding documented examples of OxTox in Scuba are difficult as highlighted by this thread.

It's not the odd's but the stakes... oxtox events kill people all the time in scuba. Certainty in the top 5 for technical divers.

The car vs. airplane analogy is misleading and oversimplified when applied to CNS oxygen toxicity and DCS. Unlike choosing a mode of transport, diving involves managing both CNS toxicity and DCS risks simultaneously, rather than choosing one or the other.

The risk of DSC can be managed by diving more conservative exposures. The risk of oxygen toxicity is less understood, and the prudent thing to do would be to dive less aggressive exposures in both the cases.

 

[tursiops]

That's basically exactly what I said, no reason to dive higher than a 1.2 for single tank recreational diving, because the gas is the limiting factor.

In managing partial pressures of oxygen (ppO2) during dives, there’s a balancing act between minimizing decompression sickness (DCS) risk by maintaining a higher ppO2 and reducing the probability of central nervous system (CNS) oxygen toxicity by running a lower ppO2. To evaluate these choices, it’s helpful to remember that risk is defined by both probability and impact.

Running a lower ppO2 increases the probability of DCS due to greater nitrogen loading, since a lower oxygen fraction means a higher nitrogen fraction in the breathing gas. This elevated nitrogen fraction leads to additional inert gas uptake in tissues, increasing the risk of DCS. The impact of DCS varies widely, ranging from minor symptoms that resolve with surface oxygen to more severe cases that require recompression treatment, drowning from DCS is not common.

By comparison, CNS oxygen toxicity events are low-probability occurrences within recommended ppO2 limits (such as 1.2 atm during working phases and up to 1.6 atm in decompression). However, the impact of a CNS oxygen toxicity event is likely catastrophic if it occurs underwater, as a seizure would likely incapacitate the diver, leading to a high risk of drowning before assistance can be provided.

Given the much higher impact of CNS oxygen toxicity (possible drowning) versus DCS (generally treatable) diving practices should emphasize conservative ppO2 limits. This approach accepts a slight increase in DCS probability due to higher nitrogen tissue loading in favor of reducing the chance of a low-probability, high-impact CNS oxygen toxicity event.

Risk Type	Condition	Probability	Impact	Overall Risk Level
DCS	Lower ppO₂ (e.g., 1.2 ATA)	Moderate	Moderate - Variable symptoms; may require recompression but rarely life-threatening	Moderate
	Higher ppO₂ (e.g., 1.4-1.6 ATA)	Low	Moderate - Reduced inert gas loading, lowering probability of DCS	Low to Moderate
CNS Oxygen Toxicity	Lower ppO₂ (e.g., 1.2 ATA)	Very Low	Catastrophic - Seizure can result in drowning	Low
	Higher ppO₂ (e.g., >1.2 ATA)	Low	Catastrophic - Greater ppO₂ increases seizure risk, leading to drowning if it occurs	High

Nice analysis, but I know all that. I think we agree, but apparently you'd rather argue.

 

[flymolo]

Nice analysis, but I know all that. I think we agree, but apparently you'd rather argue.

It's funny you should say that because i recall how earlier you wanted to argue that people don't dive nitrox for longer bottom times

 

[tursiops]

It's funny you should say that because i recall how earlier you wanted to argue that people don't dive nitrox for longer bottom times

They don't; they dive it to accumulate less N2.
Do the same (allowable) dive on air and Nitrox; on Nitrox you on-gas less N2. My point is that you often can't dive to the increased NDL of Nitrox because you haven't got enough gas to do that.

 

[crofrog]

Nice analysis, but I know all that. I think we agree, but apparently you'd rather argue.

We do agree. I don't think we're arguing in this case, but you always seem to think so.

 

[flymolo]

They don't

Then why is it all over the PADI materials for Nitrox?

 

[davehicks]

It's not the odd's but the stakes... oxtox events kill people all the time in scuba. Certainty in the top 5 for technical divers.

Technical Divers. A small subset of the diving community, of which I am one. These divers have a lot more training and knowledge to manage these issues, but also knowingly take on more risk. Even so, OxTox is a rare event.

Recreational scuba divers really don't need to spend time being concerned about OxTox. It's just not a real-world issue that will impact them.

 

[rjack321]

Are you referring to the 14 July 2007 incident or something else? Based on the limited public information available it seems unclear whether she actually toxed, or seized for some other reason.

https://caves.org/wp-content/uploads/2021/10/February_10_ACA0708.pdf

2007-07-14 Incident – IUCRR

iucrr.org

There is no way to affirmatively determine if ppO2 was why she toxed post-mortem. From day 1, her husband and one of the buddies on the dive has said it was O2 related however.

 

[boulderjohn]

The original question:

I know of a woman who toxed and died at 1.4 here in cave country.

Can you provide details?

 

[tursiops]

Then why is it all over the PADI materials for Nitrox?

You'll have to ask PADI that.
I suspect it is because it is the easiest thing to describe, and also is what means less N2 uptake if you don't make your dive longer. But PADI -- and the other agencies -- don 't like to talk about complicated things like N2 uptake...it is so much easier to just say "longer times." It is a true statement, after all.