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.