My first CO2 hit?

[acxc]

I also just had my first c02 hit a few weeks ago. I was not working any harder than usual and my scrubber was well within manufacturer limits so I'm guessing it was some other breakthrough issue. My biggest takeaway was that it was that when it actually hit, it was so much worse than what friends who've experienced one have described to me. Though i was able to bailout out (I don't actually remember deciding to, so I guess I did it on instinct), it was still basically impossible to get under control. In hindsight I ignored some of the early symptoms (confusion/anxiety/paranoia) thinking I was a little seasick and if I was ever in that situation again I would not hesitate to bailout or flush early. I never want to feel that bad underwater again. The only other interesting thing is that until it actually hit I never felt my breathing change and at no point did I get headache.

 

[Akimbo]

Not sure if the same could be said for hypercapnea.

Symptom recognition is the objective as opposed to developing tolerance. IMO, real world habituation with hypercapnia is invaluable for symptom recognition, though I'm not highly confident that breathing premixes in a classroom would accomplish the same goal.

Because of heavy work and less than ideal oral-nasal seals, hypercapnia is a common issue in commercial and military surface supplied diving. It was an almost daily experience climbing a ladder in heavy gear.

 

[Tassi Devil Diver]

Sounds like a classic case of over exertion.

 

[scubaozy]

What gas were you breathing? With ean32 @ 4ATA you will have 5-5.5 g/l gas density. You are actually vey close to recommended limits even without exertion. Add a little work on top, elevated co2 is probably expected.

 

[Brad_Horn]

I dive a JJ CCR, international edition (no dil MAV or ADV shutoff). Bailout is a single AL80 with EAN 28. Axial scrubber, rated for 180 minutes (4 degrees C and heavy workload). I have been diving the JJ for about 6 years, with a bit over 250 dives / 200 hours on the unit.

I’m very compulsive about scrubber packing and mushroom valve checks. Doesn’t mean that a CO2 hit is impossible, of course.

This was a NYC area wreck dive, second one of the day, first dive with a minor amount of deco. It was a working dive doing shipwreck photogrammetry. This involved me basically being an underwater tripod, taking thousands of photos at fixed depths and distances, while slowly circling the wreck. I was at 80 feet, about 20 minutes into the second dive, with 80 minutes on the scrubber. The temperature was 50 degrees F (10 degrees C).

There was one point on the wreck where there was a very strong localized current, and it was VERY difficult to hold position in that area, especially within the project requirement window. I worked for a while holding the camera stable and kicking hard against the current, finally gave up and swam to the wreck to get out of the current and stabilize. I felt winded, but I was able to continue on to other parts of the dive after resting.

About 5 minutes after that, I started to get a little headache, which became worse after surfacing and then over the rest of the day. By the time I got home, it was pretty severe, with no other symptoms of illness. It resolved over a few hours.

I figure I was overbreathing the scrubber. I have heard that CO2 headache can last for quite a while after you have blown your CO2 levels back down to normal, due to changes in cerebral blood flow.

I don’t think that I had a breakthrough of the scrubber or a failure of the mushroom valves. This was a shallow dive, so gas density wasn’t a likely issue. In retrospect, there wasn’t a time when I felt the need to bail out or even do a dil flush, the headache came on after I was already feeling and breathing normally again.

What do you think? Should I have bailed out? Any other insights?

Mike, those headaches hurt don't they!

You don't clarify if you're diving with a JJ-DSV, or BOV. If BOV whose?
Why is this important... If you've substituted the JJ-DSV for a Shrimp BOV for example then you've probably increased your loop WOB and likely decreased the scrubber endurance from that tested. And if you bailed off onto it your condition might not have improved much due to known high WOB irrespective of gas density!

What granular absorbent were you diving: manufacturer, type and date.
Different absorbents give VERY different results...
Were you diving something that gives less of a duration than that tested?

Rebreathers variation in performance at depth might or might not differ; see Ireland | John Clarke Online

You've already self-identified that you've overbreathed the scrubber, exceeded its safe diving envelope and had a breakthrough due to your high workload on a working dive with 100min on the scrubber at depth...

A commercial working dive with heavy camera equipment, where current and jobsite time pressures are a risk, gives a very different pre-dive planning risk assessment than a fun recreational dive.

I note you mention that the JJ-CCR has a 180min duration... But does it for your specific circumstance?
Noting that 180min is based off 3 odd scrubber tests at 40m on VERY importantly for your circumstance a PROFILE dive. And not a constant 40m BT!
The measurement (in this case) is also taken from upstream of the DSV and not from the divers mouth; so you have to take into account the DSV/BOV deadspace in your figuring and the reduction this causes.

Looking at that profile scrubber duration it was tested for only 40min at 40m, then 5min at 15m and remaining time at 9m.....
Your dive I understand was 80min mostly at 25m with a little deco and then 20min again at 25m.
So you spent 40min at 15m less than the published scrubber duration testing by JJ @QinetiQ but also roughly a further 50min odd working at 16m greater than the 180min dive profile JJ tested for.....

Controversial but based off the test data available to you and the details you've given, it looks like you can only plan on a known safe 40min BT at 25m (80ft) off each fresh scrubber fill, where a period of high workload is a consideration...

Diving at 10'C gives a benefit but how much over 4'C on your unit is pure guess work and it might not be that much of a buffer on your safety!

 

[doctormike]

What gas were you breathing? With ean32 @ 4ATA you will have 5-5.5 g/l gas density. You are actually vey close to recommended limits even without exertion. Add a little work on top, elevated co2 is probably expected.

PPO2 of 1.3

 

[doctormike]

Mike, those headaches hurt don't they!

You don't clarify if you're diving with a JJ-DSV, or BOV. If BOV whose?
Why is this important... If you've substituted the JJ-DSV for a Shrimp BOV for example then you've probably increased your loop WOB and likely decreased the scrubber endurance from that tested. And if you bailed off onto it your condition might not have improved much due to known high WOB irrespective of gas density!

What granular absorbent were you diving: manufacturer, type and date.
Different absorbents give VERY different results...
Were you diving something that gives less of a duration than that tested?

Rebreathers variation in performance at depth might or might not differ; see Ireland | John Clarke Online

You've already self-identified that you've overbreathed the scrubber, exceeded its safe diving envelope and had a breakthrough due to your high workload on a working dive with 100min on the scrubber at depth...

A commercial working dive with heavy camera equipment, where current and jobsite time pressures are a risk, gives a very different pre-dive planning risk assessment than a fun recreational dive.

I note you mention that the JJ-CCR has a 180min duration... But does it for your specific circumstance?
Noting that 180min is based off 3 odd scrubber tests at 40m on VERY importantly for your circumstance a PROFILE dive. And not a constant 40m BT!
The measurement (in this case) is also taken from upstream of the DSV and not from the divers mouth; so you have to take into account the DSV/BOV deadspace in your figuring and the reduction this causes.

Looking at that profile scrubber duration it was tested for only 40min at 40m, then 5min at 15m and remaining time at 9m.....
Your dive I understand was 80min mostly at 25m with a little deco and then 20min again at 25m.
So you spent 40min at 15m less than the published scrubber duration testing by JJ @QinetiQ but also roughly a further 50min odd working at 16m greater than the 180min dive profile JJ tested for.....

Controversial but based off the test data available to you and the details you've given, it looks like you can only plan on a known safe 40min BT at 25m (80ft) off each fresh scrubber fill, where a period of high workload is a consideration...

Diving at 10'C gives a benefit but how much over 4'C on your unit is pure guess work and it might not be that much of a buffer on your safety!

Good points, and thanks, Brad...

Stock JJ DSV.
Sofnolime 797, well within the date wiindow (expires 2025).

We had done these photogrammetry dives a number of times for our project, the increased workload due to the localized current was very much unanticipated. Never had an issue like that before, in retrospect the right thing to do on a working dive like this might have been to just skip that portion and get those images another day.

Here are the profiles. The event happened on the second (non-deco) dive.

 

[scubaozy]

PPO2 of 1.3

Ok that makes it around 4.6 g/l for 80ft/25m, it is still in the green zone. I somehow thought I read 100ft..