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

[dmaziuk]

 

[Astran]

Oh dear. You seemed to have picked up on the posts you like and ignored the ones you don't. The issue is simple: at the time you ignored what the computers were telling you, you did not yet know you were diving a conservative computer. That was a mistake, but you were lucky.

I suspected the computer was providing erroneous information and it turns out I was correct.

 

[scubadada]

I suspected the computer was providing erroneous information and it turns out I was correct.

Go back and read the posts. The Oceanic computers were not supplying erroneous information, they use one of the two common ways to track O2 exposure. It happens that this mechanism is more conservative than the alternative mechanism. The data to support the 90 minute half life for O2 elimination is hard to come by. Personally, I believe there is an O2 elimination half life versus the cliff credit given for the NOAA tables, but I have no confidence that 90 minutes is correct. If anyone has information to shed light on this issue, I would be glad to see it.

 

[Astran]

Ok erroneous might be a bit of an exaggeration but certainly the data supplied by the Oceanic in regard to 02 exposure can be taken with the proverbial grain of sea salt, especially given that under the same diving conditions your less conservative computer has never issued an 02 warning.

I carry enough gear as it is, I don't need to be carrying around a paperweight.

 

[GJC]

After reading this entire thread 3 times and reading all of the info on the links mentioned, you need to remember how NOAA came up with the oxygen limits.

The NOAA 24 hour limits are actually the max time for your dive if you have to do table 6 chamber treatment after your dive. So if you do not have to take a chamber ride, you are way below an oxygen exposure that would cause any CNS or pulmonary symptoms when your computer says you are at max.

 

[yle]

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 the instructor and the student that matters, not the agency. You're very likely correct, that long term O2 exposure is a standard in any entry level nitrox course. Whether or not the instructor covers it and the student remembers is the issue.

I can't speak for other agencies or instructors, but I know it's a standard in the PADI course. When I teach the class my students have the table (provided in the PADI materials) that allows them to calculate each dive's contribution to the total O2 exposure. We do these calculations as part of the dive planning for the class, and I advise them to consult their computer, when in nitrox mode, after every dive to develop an instinct for how much their typical dives contribute.

 

[ScubaRob0311]

Ok erroneous might be a bit of an exaggeration but certainly the data supplied by the Oceanic in regard to 02 exposure can be taken with the proverbial grain of sea salt, especially given that under the same diving conditions your less conservative computer has never issued an 02 warning.

I carry enough gear as it is, I don't need to be carrying around a paperweight.

I haven't kept up on this topic but I remember reading that your primary and back up computers both said to go up and your dive buddies computer said to go up and you still decided to stay down for 20+ more minutes?

I'm not trying to pick on you or anything but that seems very unsafe. Not only did you put yourself in potential danger but your dive buddy as well.

I'm glad everything worked out but just think about how you would feel if your dive buddy has a serious issue during that dive? Could you still justify taking that risk of ignoring 3 computers and not feel guilty?

 

[yle]

I suspected the computer was providing erroneous information and it turns out I was correct.

Hmmmm... interesting conclusion.

But... even if you thought the computer was wrong, wouldn't it be a better practice to end the dive and investigate the computer when you're out of the water? I mean, just due the remote possibility that the computer was... right?

 

[KenGordon]

Ok erroneous might be a bit of an exaggeration but certainly the data supplied by the Oceanic in regard to 02 exposure can be taken with the proverbial grain of sea salt, especially given that under the same diving conditions your less conservative computer has never issued an 02 warning.

I carry enough gear as it is, I don't need to be carrying around a paperweight.

Don’t bother arguing. The only thing more sacred than a Shearwater UI round here is the limits imposed by an Oceanic dive computer, especially their NDLs.

Personally I think you did the right thing but maybe for the wrong reasons, but now you know that these computers are stupid in this respect so can ignore them. If you do the numbers properly it is really hard to get limited by CNS toxicity doing no stop dives.

What I have learned is there is a whole universe of people taught to do this in a simplistic way.

 

[scubadada]

After reading this entire thread 3 times and reading all of the info on the links mentioned, you need to remember how NOAA came up with the oxygen limits.

The NOAA 24 hour limits are actually the max time for your dive if you have to do table 6 chamber treatment after your dive. So if you do not have to take a chamber ride, you are way below an oxygen exposure that would cause any CNS or pulmonary symptoms when your computer says you are at max.

I have never heard this, I will have to read the NOAA dive manual