Accumulated 02 following a large number of repetitive Nitrox dives over 3 days.

[Astran]

In light of this question, I don’t think that @kmarks question is irrelevant at all. Setting the computer max PO2 to 1.4 or 1.6 does not impact the running of the CNS clock. Perhaps a refresher is in order?

Yes so going forward, know that I am quite familiar with the principles of Nitrox and the CNS clock and the ramifications for absorbing too much 02 in your tissues. My thread is really about how significant a factor it was on this particular trip as compared to literally dozens more that were similar but did not cause this issue and why it may have happened on this particular trip and not the others in hundreds of EAN dives.

if you're going to tell me that I need more training, or I should already know this, or otherwise suggest that I'm a moron for not knowing basic Nitrox principals or whatever, you won't be getting a response.

 

[rhwestfall]

I've always wondered how much and what kind of diving would be necessary for this to happen..... Never imagined it possible....

and now I know....

 

[Manatee Diver]

If you round up you probably went over. If you went to the exact numbers you probably were on the borderline of max exposure.

 

[Astran]

It is not the computer setting that determines the 24 hour O2 exposure limit, it is your dive profiles.

Ok that's what I thought but it seemed like there was one or two posts that were specifically addressing the P02 setting on the computer. Got it.

 

[Astran]

You came close, but you probably didn't go over if you factor in your surface intervals.

My computer might disagree with you, at least for the 20 remaining minutes of that dive which was flashing a full 02 bar and zero DTR.

 

[JackD342]

You came close, but you probably didn't go over if you factor in your surface intervals.

Really? OP said at least 3 different computers across two divers all ran out of time, and they kept on diving. That is the very definition of "go over" the limit.

 

[rjack321]

Oxygen causes two kinds of problems.

1) If the partial pressure of oxygen is too high, it can lead to colvulsions and consciouslessness.
These typically lead to drowning.
1.4 ATM of oxygen is considered to be reasonably safe for ordinary diving (and 1.6 ATM at rest during decompression).

2) Oxygen irritates lungs. It is oxidicing, which means it burns things. In the long run it also damages and scars your lungs. This is called "pulmonary oxygen toxicity". Too much oxygen over a prolonged period of time damages lungs. Permanently. I do know a person who had to quit diving as he had been breathing high concentrations of oxygen for prolonged amounts of time (albeit not enought to cause convulsions and death).

I would assume that your computer warned of this irritation/damage to the lungs.

I'm guessing the oceanic ran up against the CNS limits as @tbone1004 posted since the surface intervals were short and the PPo2s were high.

Pulmonary limits are usually more permissive / less controlling until you get up into the 8-12hrs exposure range.
See figures 1 and 2
https://www.shearwater.com/wp-content/uploads/2012/08/Oxygen_Toxicity_Calculations.pdf

or here they are on the same graph but hard to read
Oxygen Toxicity - Signs and Symptoms | Dive Rite

Both forms of toxicity should have been covered in your nitrox course @Astran

 

[Manatee Diver]

Really? OP said at least 3 different computers across two divers all ran out of time, and they kept on diving. That is the very definition of "go over" the limit.

Using the NOAA charts I came up around 90% for the first day. And 112% for the second day, but I am rounding up. I have no idea about the third day because we don't have times.

 

[Subcooled]

Ignoring warnings is dangerous. The odds are small that you are that superhuman who can take more abuse than others.

If the dive computer says no, it's a no.
Period.

 

[kmarks]

Don't really need these sorts of comments thank you.

It wasn't meant to be accusatory, just curious. I don't know anything about the other agencies, but I can just about quote it from the SSI EANx manuals for you.

Yes so going forward, know that I am quite familiar with the principles of Nitrox and the CNS clock and the ramifications for absorbing too much 02 in your tissues. My thread is really about how significant a factor it was on this particular trip as compared to literally dozens more that were similar but did not cause this issue and why it may have happened on this particular trip and not the others in hundreds of EAN dives.

if you're going to tell me that I need more training, or I should already know this, or otherwise suggest that I'm a moron for not knowing basic Nitrox principals or whatever, you won't be getting a response.

You came here looking for an answer to a question and you got several thorough, well-thought answers. Nobody has called you a moron, or said anything disparaging, only suggested that if you are unfamiliar with a key concept of the EANx training, you may want to review or take a refresher on it.