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

[BRT]

What certification agency did you use for your EANx training? I'm only familiar with SSI because that's what I do, but I'm pretty sure that the CNS clock time is pretty similarly taught across all agencies. It's in Section 4 of the SSI EANx digital manual.

SSI even has a CNS Clock Exposure Time Table that is a little different from what JackD342 said above. At ppO2 of 1.4, you are limited to 180 minutes of total time in 24 hours and 150 minutes on a single dive. At 1.6 like you were, you are limited to 150 minutes in 24 hours and 45 minutes in a single dive.

What happened is probably that after your long day on Saturday, with an especially heavy morning load, you were saturated on your clock time during your Sunday morning dives, but by the time you did the third and fourth dives, a sufficient amount of time had passed to regain some clock time.

Whatever happened, you were already pushing limits by using 1.6 as your acceptable ppO2 level. I wouldn't have pushed the clock time limit and ignored my computer's warnings. But, that's my decision.

They were not at 1.6 PPO2. They were a little over 1.0.

 

[Astran]

@scubadada is diving with two different computers, programmed with two different rule sets. Neither one is right or wrong, they are just different. He has made a personal decision to follow the more liberal rule set for O2 exposure. He has NOT decided to completely ignore all limits and warnings, the way that you did on that dive in question. I don’t think anyone is telling you to just ignore any and all O2 exposure limits and warnings. If you want to choose to follow a different, more liberal rule set, then go buy that other computer.

Hopefully @scubadada can weigh in on this, but I'm going to wager a guess that his other computer, the less conservative one, tells him to end his dive due to reaching 02 limits.. probably never.

That's quite different from using 2 computers with different algorithms to determine a favorable NDL bottom time.

 

[scubadada]

Correct, neither my Nitek Q or, now, my Teric, has ever gotten close to daily O2 exposure.

The Oceanic computers display the lowest of the values between NDL, O2 exposure, or air time remaining, if air integrated, as the dive time remaining on the main screen. These carry labels, Air, NDL, O2, to let you know which one is controlling the dive. When you exceed the O2 limit, the dive time will register 0, as it did for @Astran . The NDL and/or air time remaining can still be found on alternate screens and/or bar graphs. It is easily possible to continue diving safely, within NDL, after reaching the O2 limit. It sounds to me, that is what Astran and buddy did.

 

[rhwestfall]

It is easily possible to continue diving safely, within NDL, after reaching the O2 limit. It sounds to me, that is what Astran and buddy did.

Not convinced that you should be using that word (red/bold above).... Though not something immediately apparent like convulsion, the potential injury is real (and seems to be unpredictable)... Again, always pushing to the limits is a questionable practice.

Although, this is just my opinion.


YMMV

 

[LiteWeight]

The PO2 setting on your computer is only for the MOD alarm setpoint. It has nothing at all to do with any calculations or CNS calculations.

That being said, if you're going to ignore your computer, why carry it?

You don't need a computer. I've performed many dives to 200' with no computer.

 

[tursiops]

You don't need a computer. I've performed many dives to 200' with no computer.

Hey, tell the rest if the story! Air? Single tank?

 

[kmarks]

They were not at 1.6 PPO2. They were a little over 1.0.

We don't know exactly what ppO2 he was at throughout the dive because even a square profile isn't actually square, but you're right, he was never actually at the ppO2 1.6 that he was allowing himself to reach. I only mentioned that as an example because he said that he had accepted the risk of setting his computer's alarms to go off at ppO2 of 1.6 and I was pointing out that whatever ppO2 you are currently experiencing, it makes a difference on your CNS clock time, and if you were to dive the clock time tables (as opposed to using a computer), you have to assume a square profile, just like diving on the more familiar NDL tables.

 

[dmaziuk]

I don’t know if this counts as O2 toxicity that you are referring to, but my basic computer (Cressi Leonardo) allows me to change the pO2 setting anywhere between 1.2 to 1.6.

PO2 is only relevant if you're riding the limit all the time. What Leo manual doesn't say is whether it's using the "rolling window" or "half time" method to draw that little O2 toxicity bar graph. In fact I'd say its manual is actively misleading on the subject.

 

[Astran]

That being said, if you're going to ignore your computer, why carry it?

Because, well you know, I sometimes use it for other stuff that I think is more important [than ultraconservative max 02 settings that can be safely ignored], such as NDL limits, gas supply remaining, elapsed dive time, depth, ascent rate, that sort of thing.

Why did I ignore my computers 02 alarms given that both of my computers and my buddies computer all indicated violations?

Because it just didn't seem right. Because we were at about 60' at the time. Because I didn't think our dive profiles were all that much different than dives I've done 100s of times before. That's all I got..

Although it was a somewhat impulsive decision it appears to have been the correct one given the information provided on this thread primarily by @scubadada.

 

[rjack321]

They were not at 1.6 PPO2. They were a little over 1.0.

Huh?
They weren't at 1.6 but almost all the dives were over 1.2 and closer to 1.4
109ft on EAN32 is ppO2 1.37
96ft on EAN36 is ppO2 1.4