Yep what WFO said. Always know your Po2. The electronics , kit etc are just there to assist you in decision making not make the decision for you. It’s a slight shift of mind. So Paul H talked about one incident where 2 cells were current limited , cell 1 went sky high the diver suffered hyperoxia. The unit would’ve been using voting logic and injecting o2 based on the 2 cell readings that were limited , so pissing in o2 based on 2 cells that could never read that high.
So our manual defence to that is clearly having prepped the unit and checked it before entering the water , then in the water injecting a small amount of o2 into the loop to push the po2 above set point. Linear response across the cells then flush back down. No harm in doing this a few times through a dive , particularly as cell failure , I understand, can be more common when the scrubber stack is up to temperature, for the inspo that’s about 20 mins and humidity is increasing.
This was one of the examples where hyperoxia brought unconsciousness followed by drowning.