Hi again Johnny,
Just for completeness, if you read my long earlier post there may be a perfectly good reason for this. These events may have been due to CO2 retention. Remember that this can happen in the complete absence of any CO2 rebreathing, and so you would not expect any warning from the RMS or temp stick. You might ask why bailing out would help in that setting. Well, the divers probably bailed out onto a lower work of breathing system which would definitely help in a retention situation, and the fact that they bailed out indicated that they were well aware they had a problem and would have been consciously responding to their perceived need to breathe more (rather than sub-consciously not responding which is what leads to retention). I am not saying you are wrong, but rather I'm reminding you that there is a perfectly plausible explanation why a diver could have a CO2 hit with no warning from a temp stick or the RMS.
I mentioned in the last paragraph of the quoted post that CO2 retention is exactly why some of these systems would give zero indication of a CO2 issue, despite the diver experiencing symptoms. It's a pretty insidious failure mode. And, it's one of my arguments against "reliance" on current methods of CO2 monitoring.
This must have been with one of the infra-red CO2 monitors because a temp stick would not do this and the rationalisation you illustrate here exemplifies one of the problem with these CO2 monitors. If the diver is not going to believe the monitor, then there is not much point in having it. If this occurred in an inspo (for example) it could mean that the diver left the o ring and spacer out of the centre section during the assembly leading to bypass. If, however, the diver tells himself that the scrubber is new so the monitor must be wrong, then the point of having it is completely lost. Such rationalisations are all the more likely if there is a known incidence of false positives, which make it easier for the diver to dismiss alarms.
Yep, exactly my point. Again, the reliance on a single system to indicate a failure is dangerous. A single system with no redundancy is even more so. Because there are several potential failure modes that can occur that do not cause the system to indicate a failure state, then the reliance on it as an indication is compromised.
