My first CO2 hit?

[doctormike]

I recently had what I believe was a hypercapnic episode on a rebreather dive, and I’m interested in your thoughts.

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?

 

[kaylee_ann]

Seems like it could've been, due to the increased workload you had. From my pretty basic understanding, that can cause a CO2 buildup. Since you felt winded afterwards for a little, it definitely seems like it was a bit intense. Now- here's one part I definitely am unsure about but it's my theory- maybe the increased CO2 level you had from heavy breathing overwhelmed the scrubber for a minute. You have a much greater knowledge of rebreather mechanics, I'm sure, so take that last one with a grain of salt.
And sure, that's a relatively shallow dive, but still a bit over 3 ATA.
Here's an article I found- carbon-dioxide-narcosis-and-diving
"The primary cause for CO2 elevation during diving, then, is exertion coupled with increased gas density. Stress increases the metabolic rate and can contribute to increased CO2 production. Rebreathing expired gas containing CO2 will also elevate PCO2." "Rebreathers can also elevate CO2 due to malfunction of the one-way valves or exhaustion of the CO2 absorbent."
If anyone has a more in-depth understanding, and I'm way off- please correct me.

 

[sprockjohnson]

Sounds like the scrubber was overbreathed. I haven't experienced that on any of my rebreathers but am always trying to be conscious of workload. DPVs reduce finning workload tremendously. I have, on the other hand, had similar symptoms while overexerting myself on open circuit as I was trying to move my boat anchor at about 80' to get it better secured. Same type of headache after huffing and puffing for a few minutes at depth but it went away soon after I stopped and resumed normal breathing. Again, this was on open circuit. I attributed it to CO2 but it could have been something else entirely.

 

[davehicks]

I think we had a nearly identical thread on this topic just a few weeks ago, but that involved deeper dives. Heavy workload on a rebreather is to be avoided for just this reason. It is very possible to push more gas through the scrubber than can be absorbed and that can result in a co2 hit.

Bailout is not needed if the cause of so clear cut. Better preventative steps during heavy work are what is called for. If you do find yourself breathing hard for a minute while on the loop, do a preventative flush to avoid any excess CO2 buildup.

 

[doctormike]

I think we had a nearly identical thread on this topic just a few weeks ago, but that involved deeper dives. Heavy workload on a rebreather is to be avoided for just this reason. It is very possible to push more gas through the scrubber than can be absorbed and that can result in a co2 hit.

Bailout is not needed if the cause of so clear cut. Better preventative steps during heavy work are what is called for. If you do find yourself breathing hard for a minute while on the loop, do a preventative flush to avoid any excess CO2 buildup.

Yes, and my post was adapted from that thread. I had said I was going to post it so that people could critique my actions in a separate thread... Sorry to silt up the forum!

That's good advice. In restospect, in addition to resting, I should have flushed the loop.

Thanks!

 

[davehicks]

I am not too familiar with the JJ, and i am curious how big the counter lungs are?

 

[doctormike]

I am not too familiar with the JJ, and i am curious how big the counter lungs are?

8 liters, back mounted.

 

[rddvet]

When I took a hit my headache came on like a freight train or a baseball bat to the head. It hit me fast and hard. I also had severe anxiety that was very hard to break, then my sac went up. I was able to bail out and fix the issue after about 10 mins of breathing oxygen on the surface

 

[Akimbo]

I recently had what I believe was a hypercapnic episode on a rebreather dive, and I’m interested in your thoughts.

A commercial diving school instructor told students to under-ventilate their hats in order to become familiar with CO2 buildup symptoms. This was not a bad training procedure because the instructor was in constant voice communications and standby divers could follow their umbilical to intervene.

I often thought that rebreather training should include breathing various pre-mixes with CO2 in a classroom setting. You can describe symptoms all day but there is nothing like experiencing them.

 

[doctormike]

A commercial diving school instructor told students to under-ventilate their hats in order to become familiar with CO2 buildup symptoms. This was not a bad training procedure because the instructor was in constant voice communications and standby divers could follow their umbilical to intervene.

I often thought that rebreather training should include breathing various pre-mixes with CO2 in a classroom setting. You can describe symptoms all day but there is nothing like experiencing them.

Simon Mitchell looked into that idea for hypoxia training a few years ago (like in aviation), and concluded that prior experience didn't help. And of course there are some serious risks of hypoxia, even on land.

Not sure if the same could be said for hypercapnea. Maybe people who are predisposed to arrhythmias or something? Maybe OK to do that with CO2 in a very controlled setting.