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

Imperfect CO<inf>2</inf> removal mechanisms of CO<inf>2</inf> scrubbers often lead to the existence of CO<inf>2</inf> in gas inhaled by a diver from underwater rebreathers. This may cause CO<inf>2</inf> related rebreather faults and subsequently would increase the risk of human injuries. We introduce a stochastic model for three CO<inf>2</inf> related rebreather faults: CO<inf>2</inf> bypass, scrubber exhaustion, and scrubber breakthrough. We establish the concept of CO<inf>2</inf> channeling that describes the cause of the faults and present a CO<inf>2</inf> channeling model based on a stochastic process driven by a Poisson counter. This helps us to investigate how CO<inf>2</inf> flow inside the rebreather is affected by CO<inf>2</inf> related faults. Fault diagnosis/prognosis algorithms are developed based on the stochastic model and are tested in simulation.

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