As I mentioned in a post yesterday, I had what I'm now presuming is a CO2 breathrough on my unit last weekend. I'll state up-front that the scrubber fill was well within it's recommended lifetime.
I was diving the Everleigh, which is in about 45m and was was running towards the end of the planned bottom time, around 35 to 38 minutes into the dive, when I started to feel very out of breath. This progressed to the point where it was almost impossible to breath, with the rapid breathing being almost uncontrolable. As a result I got very stressed, and despite having 18/40 as a diluent gas felt distinctly narked (confused, slow to react).
I desperately wanted to go up, right away, and the thought of the oncoming ascent and decompression filled me with a sense of despare. I managed, barely, to control my panic and deployed a delayed SMB and started up with the assitance of my buddy.
Although some of the cannoical symptoms such as headache or drowsiness were not present, everything about the incident fits with a CO2 breathrough, especially the fact that I felt better during the ascent, where the gas being dumped from the loop and the extra O2 being added by the unit would reduced the percentage of CO2 present.
During our time on the bottom the weather had deteriorate quite severely and I had to work hard to get back onto the boat in force 7 conditions, this resulted in another incident on the lift where again it was impossible for me to get a breath. This time however I violently spat the mouthpiece out and preceeded to take great gulping breaths, I had to be assisted onto the boat and took some time to recover.
During the incident, I can honestly say I didn't recognise it as hypercapnia, I was feeling confused, paniced, and paranoid. The thought of bailing out to OC, even if possible due to my rapid breathing, never even occured to me in the circumstances. If it wasn't for my buddy who babied my through my decompression I probably wouldn't have managed the ascent, I didn't feel "well" until the 6m stop.
I've now broken down the unit down. Looking at the cannister O-ring the O2 grease I'd applied to to it had gone, well "lumpy" is the best way to describe it, "sticky" also springs to mind. Not really what you'd expect from grease, I'll stick to silicone grease in the future, if at all. I've ordered new O-rings, and some scrims just in case, from Ambient Pressure which should arive for the weekend when I'll be getting back in the water to dive the Salsette.