They want to show that a partially failing scrubber does not cause direct problems, but later maybe yes.
With more than 1000 hours on ccr, yesterday I had my first strange feeling what must be a CO2 problem on a really shallow dive with my ccr. I was diving my ccr with new cells, the scubber has a CE limit of 3 hours and only 45-60 minutes were done on this scrubber a week before. Why do I write 45-60 minutes? That has to do with a teaching dive, we practised some skills like bo, descends, etc, so went up for a couple of times, down again, flushes, etc. So I did not feel anything strange during that dive, where the in wate time was 65 minutes, but the time under water some less. So if there was something wrong with this scrubber, I would probably not feel it because of breathing normal air between excersizes. Max depth was 15m.
So yesterday I took my ccr again with the idea of doing 2 shallow dives, or 1 longer one on ccr and the second on oc. This was a fun dive, and after half an hour we split up because I wanted to take some pictures of small snails. I also checked the celles as they were new, if they lookedTo take these pictures, I was diving in strange positions, but really shallow, between 5 and 8m depth. I felt some headache starting, but not that serious. I also had to pee. After about 75minutes I had to decided that I had to go out due to my peeing need. I swam back to the entrance point, a little bit faster than normal because I was not looking anymore for small critters. But it was not a hurry swim. Only at a depth of 4m. I only felt that I was a little bit out of breath, something that is not normal, even not with this a little bit faster swimming. But I still could hold my breath. I tested this because I was thinking that this could be CO2. Yes, I could swim back at surface, yes, I could do a bo, but then was already back to the entrance before I had to take action. When taking off my fins, I was still a little bit out of breath. For sure not normal. Back at the car I had only a slight headache left. Drank some water, and for the second dive I took my oc twinset.
All signs are there for a small CO2 breakthrough, nothing that you will see with a prebreathe, nothing that I felt within the first hour of the dive, it started around 75 minutes, when I was getting a little bit cold also. I checked all at home again, no orings broken, all orings in place, no leaks in the mouthpiece (I also had checked this before assembling), so I know my unit must be ok.
The tempstick still did show 5 out of 6 stripes.
If I was deeper or had been further away from the entance point I had to do a bo or swim back at surface. I don't have a CO2 sensor, but have tempstick, but haven ever seen a breakthrough on the tempstick (have seen this with another diver). On the dive with the twinset, I did not feel anything strange and also no headache appeared again.
So everything is checked, even a prebreathe, but nothing was wrong then. But if you want to test if people feel a partially failing scrubber, the test mentioned above is a good one. You see that most people won't feel it then. If a scrubber only filters out 99% of the CO2, it will take a while before you feel it as a diver. This is what this test shows. If the prebreathe would have taken 30 minutes, more would have gone from the loop with a partially failing scrubber.
So this week I will dive my unit again before going to trimix depths next week.
But I won't say a prebreathe is useless and a waiste of time. There are failures that can be found then. But not all.
