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

[tursiops]

Here is another attempt to explain the "limit" issue.
There are TWO different limits with oxygen: (1) maximum depth, usually controlled by allowing for PPO2 of 1.4 or 1.6; and (2) maximum exposure time, the "oxygen clock" that has been referred to. This is the one that the OP appears to have violated. The maximum allowable exposure time to PPO2=1.4 in a 24h period is 150 minutes, but at a PPO2=1.6 is only 45 mins. By setting his computer for 1.6, he shortens his allowable exposure time.

If he sticks with 32%, the PPO2 is less, usually les than 1.4, and he is less likely to violate any limits.
If he insists on high % Nitrox, he'd be well advised to avoid too much oxygen exposure; he could help himself a lot by changing his max PPO2 to 1.4, and get more time.

 

[dmaziuk]

I went and looked: it turns out my computer's manual calls it "CNS toxicity" display and claims the will stop flashing if the diver ascends to < .6 PPO2. Oceanic manuals are way better at describing what it actually tracks.

 

[Jcp2]

I don't know of any computer that allows a diver to change the O2 toxicity settings.
Shearwater allows you to change the percent CNS that triggers a warning. But the actual limit is the same.

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.

 

[Manatee Diver]

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.

That just changes the MOD that it starts to beep at you.

Some computers, like Suunto, even increase your entered percentage by 1 for O2 calculations.

 

[BackAfter30]

Here is another attempt to explain the "limit" issue.
There are TWO different limits with oxygen: (1) maximum depth, usually controlled by allowing for PPO2 of 1.4 or 1.6; and (2) maximum exposure time, the "oxygen clock" that has been referred to. This is the one that the OP appears to have violated. The maximum allowable exposure time to PPO2=1.4 in a 24h period is 150 minutes, but at a PPO2=1.6 is only 45 mins. By setting his computer for 1.6, he shortens his allowable exposure time.

If he sticks with 32%, the PPO2 is less, usually les than 1.4, and he is less likely to violate any limits.
If he insists on high % Nitrox, he'd be well advised to avoid too much oxygen exposure; he could help himself a lot by changing his max PPO2 to 1.4, and get more time.

I think you missed here. The settings in a Shearwater (I won’t speak to any others, but I’ll be surprised if this isn’t universal) for PPO2 are used to determine MOD and set trigger levels for warnings. It should have nothing to do with the CNS clock.

The CNS clock might be better named a counter as a clock is a constant rate counter. The CNS clock in your computer are tallying your actual PPO2 exposure and “counting” up at a rate proportional to the PPO2 level at any given moment in your dive. Shearwater displays not a time, but a percentage of accepted allowable exposure.

Not related to settings; related to dive profile, as mentioned above.

 

[pauldw]

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.

Could it be that you've been riding the limit frequently, and finally edged over? Nitrox isn't for deep diving, it's for mid level diving.

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.

I don't think anyone here cares whether they get a response from you. I'm guessing most everyone here cares that you learn you shouldn't ignore your dive computer (especially multiple dive computers saying the same thing), even if you believe you're smarter than the computer.

 

[rjack321]

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.

That is the MOD setting - there's no time function in the MOD

The max single exposure CNS time limits shown in this table don't change
Shearwater and the CNS Oxygen Clock - Shearwater Research

the OTUs (aka whole body or pulmonary toxicity) from NOAA and reiterated in Bennet and Elliot don't change
OTU's. Where do the limits come from?

 

[BlueTrin]

That is the MOD setting - there's no time function in the MOD

The max single exposure CNS time limits shown in this table don't change
Shearwater and the CNS Oxygen Clock - Shearwater Research

the OTUs (aka whole body or pulmonary toxicity) from NOAA and reiterated in Bennet and Elliot don't change
OTU's. Where do the limits come from?

Thanks the table for the CNS on Shearwater is interesting.

 

[tursiops]

I think you missed here. The settings in a Shearwater (I won’t speak to any others, but I’ll be surprised if this isn’t universal) for PPO2 are used to determine MOD and set trigger levels for warnings. It should have nothing to do with the CNS clock.

The CNS clock might be better named a counter as a clock is a constant rate counter. The CNS clock in your computer are tallying your actual PPO2 exposure and “counting” up at a rate proportional to the PPO2 level at any given moment in your dive. Shearwater displays not a time, but a percentage of accepted allowable exposure.

Not related to settings; related to dive profile, as mentioned above.

The max single exposure CNS time limits shown in this table don't change
Shearwater and the CNS Oxygen Clock - Shearwater Research

I'll try and make my point again.
Look at the Shearwater link; it is as good as any. You get 150 mins (in a 24h period) at PPO2=1.4. If I've set my PPO2 max at 1.4, then presumably I'll get 150mins that day. But from the Shearwater table I only get 45 mins at PPO2=1.6. So if I've set my PPO2max at 1.6, and dive to that limit, I only get 45 mins allowable exposure.
So it isn't that setting your PPO2 max changes the allowable clock exposure, but it DOES change what that number is that is the one you need for your diving.

 

[Astran]

I have no idea about the third day because we don't have times.

Thanks for pointing that out- first post is updated to show ̶d̶i̶v̶e̶ bottom times for the last 4 dives.