CO2 Breakthrough

[hornetplt]

Is it possible to get an early CO2 breakthrough with high VO2(high CO2 generation) using a standard baseline radial scrubber and fresh sorb. I realize that there are many variables associated with scrubber design, type of sorb, length of use, water temp, depth, etc. The reason I am asking is that I recently had a CO2 hit after 5 hr of use with my Azimuth(rated for 6hr warm water, 8-12 grade, diving within recommended depth limits) and the symptoms I experienced were exactly the same as my first training dive with the unit. Those were an extreme headache, aching kidneys(I think) and an uncontrolable urge to breathe through my nose(I had to literally hold my nose closed to prevent breathing through nose). During that initial training dive, my instructor and I experienced a pretty decent current and fought it for most of the dive. My breathing rate was very high and accordingly VO2 and CO2 production must have been way up there. I experienced the same symptoms as the dive with 5hr old sofnolime.
I have been following a number of scubaboard posts on scrubber duration and have learned more than I ever learned during my rebreather instruction. I don't want this thread to turn into a discussion about specific rigs or scrubbers, but an assessment of CO2 breakthrough as a result of high diver workload(increased CO2 production).
My Azimuth is a manually controlled CCR and have been diving with it for about a year. Thanks in advance for the help/recommendations!

 

[pipedope]

You can easily get a CO2 breakthrough situation in 5 hours working hard on a 6 hour scrubber.

You can also get into hypercapnia working hard even if the scrubber is still good or you are diving open circuit. In commercial work the dive sup will sometimes tell us to slow down if we are pushing too hard.

Prevention is better than cure.

 

[caveseeker7]

That is one hell of an intresting post, and I'm quite curious about the responses it will elicit. As I just posted the other day, my knowledge in regards to scrubber design isn't close to where I would like it to be.

But here are a few thoughts that come to mind:
The subject of involuntary breathing through the nose was recently discussed at Dive-Oz , appearantly several people experienced it on their rebreathers with backmounted counterlungs when in a head down position.
None however head- or kidneyaches (the latter by the way are new to me).
So depending on you position during the dive(s) the aches and breathing issue may not be related.

The scrubber rating given for OMG rebreathers here in the US always struck me as pretty optimistic considering the amount of absorbant and general design of the scrubber. While OMG without a doubt has some of the better designs, 6 hrs seems rather liberal.

In Germany the Azimuth is rated to 3hrs., and they tend to be pretty anal when it comes to exact numbers. Therefor I for one wouldn't push my scrubber as far as you do. While different in design, the Dolphin has the same rating, which was ammended by Dräger for warmer temps and lower (more realistic) RMV to 4 hrs.

While I would check back with one or two of the people I know that understand these issues better than I do before applying these numbers to the Azimuth, they seem to be quite reasonable.

Finally, do you have an O2 monitor in the loop and did you note your pO2?
Gases tend to interact with the body not just by itself, but also as the mix. A lower than ideal pO2 may well have increased your susceptibility for CO2, and the two (lower pO2 and higher pCO2) usually go hand in hand when exhausting yourself.

Stefan

 

[MikeR]

Sounds like you overbreathed the unit. I've had co2 issues with a new scrubber when working extremely hard. Generally just slowing down resolves the issue. From your description I would say the co2 was a result of your respiration rates, not the scrubber duration.

On a side note, I have a friend who when working hard underwater almost always began to nose-breathe. He always thought it was a bye-product of the workload and heavy breathing. He also suffered from sleep apnea. When doing a sleep study they found a sinus issue that was corrected surgicly. He has reported no further urge to nose-breathe. Something to think about.

 

[BigJetDriver]

---They found a sinus issue that was corrected surgically. He has reported no further urge to nose-breathe. Something to think about.

So, Mike, you're saying that surgery changed your friend from a snooty nose-breather to a knuckle-dragging mouth-breather like the rest of us? :11:

Rob

 

[hornetplt]

Caveseeker,
I have 2 ppO2 gauges p-ported into my Azi and run a ppO2 between 1.2-1.4, depending upon how much time I invest in monitoring my ppO2.
With regards to the nose breathing business, I have NEVER experienced this urge EXCEPT for these 2 instances. During my CO2 burnthrough, I was diving with very little workload & not in the facedown position. A very strange feeling that I can only attribute to excessive CO2. Never felt this way before during any of my 400+ dives.
Oh, by the way, i'm probably getting a PRISM next year. A very complete unit for the price that suites my diving needs perfectly. Maybe you could float me anything you would like to share about your personal experience with the unit.
Thanks for the responses on this topic! If I have learned anything from my first year with the Azimuth(& previous 15 years open circuit) is that the knowledge base required for being a safe and successful rebreather diver is stagering. So much of what goes on is just not covered in the basic training. Even after prepping myself by reading Jeff Bozanics book and other pertinent publications months before my initial training, following procedures to the letter and doing nothing unsafe.......there is so much more to know! I have gained so much from the topics presented here, and I certainly appreciate the time and effort to address these concerns! I hate scaring the SH_T out of myself!

 

[padiscubapro]

Caveseeker,
I have 2 ppO2 gauges p-ported into my Azi and run a ppO2 between 1.2-1.4, depending upon how much time I invest in monitoring my ppO2.
With regards to the nose breathing business, I have NEVER experienced this urge EXCEPT for these 2 instances. During my CO2 burnthrough, I was diving with very little workload & not in the facedown position. A very strange feeling that I can only attribute to excessive CO2. Never felt this way before during any of my 400+ dives.
Oh, by the way, i'm probably getting a PRISM next year. A very complete unit for the price that suites my diving needs perfectly. Maybe you could float me anything you would like to share about your personal experience with the unit.
Thanks for the responses on this topic! If I have learned anything from my first year with the Azimuth(& previous 15 years open circuit) is that the knowledge base required for being a safe and successful rebreather diver is stagering. So much of what goes on is just not covered in the basic training. Even after prepping myself by reading Jeff Bozanics book and other pertinent publications months before my initial training, following procedures to the letter and doing nothing unsafe.......there is so much more to know! I have gained so much from the topics presented here, and I certainly appreciate the time and effort to address these concerns! I hate scaring the SH_T out of myself!

Training is the key not every instructor conevys the same information to his/her students. Not all instructors are created equal so they can only convery what they know and experienced..

There are too many quickie classes out there...