Disclaimer : this "article" is the fruit of my one imagination and as such cannot be treated as good advice.
It is merely a summing-up of a topic which I considered still underrated in the field of CCR diving.
In the same order of idea I am French so please have some tolerance with my English... thanks in advance.


Is CO2 the culprit?

I wondered for a long time about the influence of CO2 in diving accident and more specifically on CCR diving accident.
OK, everyone knows about hypercapnia and how difficult it is to completely avoid it but let me rephrase the usual (good) advices:
-proper check of check-valves on your mouth piece.
-proper storage of your new sorb.
-proper check of the sorb (duration of use if already used, proper packing)
-depending on the rebreather, proper installation of the cartridge.
-in general following a check-list for preparing the machine and pre-dive checks are good ideas since if the WOB is affected it will negatively influence the presence of CO2 in the loop.
-pre-breathing is a good idea but reports exist that CO2 issues might not be easily detected at this stage.
-efforts at depth are not a good idea, if you have to do them you should carefully monitor your breathing rhythm in order to avoid to go too far with your hyperventilation... Ok easier said than done.
-for the same reason, helium is good in the perspective of CO2 intoxication (because of its low density) it provide a lower WOB than the equivalent N2 mix.

I might forget some but that seems to be a good start.

I will not treat how to react a CO2 crisis since it has been very much debated in the past so beside the usual "if you feel uneasy bail-out". The way you do it is opinion-school-instructor-equipment dependent so... You are on your own here...

Here I will try to put together a few thoughts about the other suspected influences of CO2 intoxication.
Some of my thoughts are personal, and are not demonstrated or published or whatever. They are just a product of my own (common) sense and as such not everybody may agree... no problem.

First of all the obvious. CO2 intoxication will impair you not only physically but also mentally. The obvious conclusion here is any bailout procedure or other action you might want to take cannot be convoluted. In other words if you intend to do anything even remotely complicated while CO2 intoxicated, you are not going to make it.

Here I start with a piece a personal wisdom(?) that you never find in any manual (that I know of). If you are the victim of CO2 onset keep in mind that you put yourself also at risk with you decompression. It seems logical to me that your table or decompression computer you are using does not account on the excess of CO2 you are loaded with.
It could be for me one of the possible explanations of why a deco schedule works every time for you but one day...
In scientific words it could explain the variability of individual off-gassing variability.

Something else that everybody admit is hypercapnia is very detrimental to O2 toxicity. It can be one of the explanation of some diver convulsing underwater without exceeding the recommended pO2 or CNS clock.

CO2 is very narcotic (that is an accepted by everyone) so hypercapnia is obviously not favourable in term of narcosis.

I imagine some of the effects of CO2 intoxication are still eluding me but I see that as a decent start for any beginning rebreather diver.

Do not hesitate to post positive criticism so everybody can benefit fom it !

Dive safe