Oceanic Veo 3.0 - O2 Sat Incorrect

[DiverInSF]

Hoping to get some input on a dive computer problem.

I have an Oceanic Veo 3.0 that's been with me for 200 dives and that's generally in good condition. I just came back from a LOB trip, where we were doing 4-5 dives/day on Nitrox 32. About half way through the trip, my computer started sounding the O2Sat alarm. By the end of dive 2 for that day, I was at 80%. This baffled me and the dive crew b/c I absolutely wasn't pushing the limit on depth or NDL and the EAN setting was confirmed (and reconfirmed) correct. Checked against computers of my dive buddies (similar profile, same Nitrox mix) and their O2 sat was in the 10-15% range. The general consensus is that my computer had gone a bit strange.

Anyone else have this experience? And any thoughts on what to do next? I don't want to toss a perfectly good computer, if the problem can be rectified, but I also want to be able to trust my computer on an extended dive trip.

 

[scubadada]

Hi @DiverInSF

I have been diving an Oceanic VT3 for 11 years, I have exceeded 100% exposure many times. How could this happen? Oceanic uses the NOAA exposure limits with a 24 hour rolling time period. This is actually how the tables were designed to work. If you do 4 dives a day, there will be 5 dives in the 24 hour period before you get credit for O2 elimination. Many dive computers use a 90 min O2 elimination half life, as does my Shearwater Teric. On my Teric, I have never been above a CNS O2 exposure of 44%. I have always disregarded the O2 warning on my VT3. The only nuisance has been having to go to alternate screens or the graphic to follow my NDL

See this old thread for a discussion of the topic, includes many references Theory behind the half-life of CNS toxicity? I have not learned much since then.

The more you dive, the more you learn

 

[scubadada]

Take a look at the NOAA oxygen exposure table:

Applying the NOAA limits, in SE Florida I often do 4 dives per day with 36% nitrox. If I did those 4 dives at a depth of 60 feet, for 1 hour, I would be at 80% exposure after my 1st day. My dives often have a deeper portion and/or are over an hour, so my exposure might be a bit higher. On the 1st dive of the next day, I would still be in the 24 hour window before getting any credit for oxygen elimination. I would be flirting with or exceeded 100% exposure until I got credit for a dive, and would then drop back down to around 80%. I would then be alternating between 80 and 100% until I took a break from my 4 dives per day schedule.

Using the 90 minute oxygen exposure half life, each dive would have the same exposure, but I would get credit for all the time I spend above a pO2 of 0.5. Again in SE Florida, the average surface interval between dives 1&2 and 3&4 is about 45 min. The lunch break is usually around 2 hours. As I posted earlier, the highest O2 exposure I've had at the end of 4 dives is 44%. I always start the next day at zero.

Remarkably large difference between the two methods. How should CNS O2 exposure be monitored? I don't really know. As a physician/scientist, it make intuitive sense to me that there should be an O2 elimination half life. Is 90 minutes the elimination half life? I don't know that either. It does not make sense to me that there should be abrupt O2 elimination credit at the end of a 24 hour window.

 

[DiverInSF]

Hi @scubadada

Thank you! This is extremely informative (both threads) and sheds a lot of light on the situation. Knowing what I know now, I'm surprised I haven't run into this sooner.

 

[scubadada]

Hi @scubadada

Thank you! This is extremely informative (both threads) and sheds a lot of light on the situation. Knowing what I know now, I'm surprised I haven't run into this sooner.

It still takes 4 or 5 dives with at least one dive the next day to get to 80 or 100%. I have rarely dived 36% outside of SE Florida, where it is commonly banked, along with 32%. Most banked nitrox is 32%. In my 60 foot depth example, 36% gives you a pO2 of 1.0 and 32% gives you a pO2 of 0.9. So, with 32%, you get 60 more minutes per 24 hour period, significantly more.

It is not unusual for me to hit 80 or 100% diving 36%. I hit 80% when diving 32% occasionally, not sure if I've ever hit 100%, that would take 6 hour dives within the 24 hour window in my example of 60 foot dives