Diagnosis and prognosis of scrubber faults for underwater rebreathers based on stochastic event models

Imperfect CO2 removal mechanisms of CO2 scrubbers often lead to the existence of CO2 in gas inhaled by a diver from underwater rebreathers. This may cause CO2 related rebreather faults and subsequently would increase the risk of human injuries. We introduce a stochastic model for three CO2 related rebreather faults: CO2 bypass, scrubber exhaustion, and scrubber breakthrough. We establish the concept of CO2 channeling that describes the cause of the faults and present a CO2 channeling model based on a stochastic process driven by a Poisson counter. This helps us to investigate how CO2 flow inside the rebreather is affected by CO2 related faults. Fault diagnosis/prognosis algorithms are developed based on the stochastic model and are tested in simulation.