I have a question about the decompression algorithm that we rebreather divers use. My understanding is that these algorithms were designed for OC where the exact gas contents are know.
When we are using our computers the only thing we know is the ppO2 in the loop because we have the O2 sensor to measure this directly. But how does the computer know the ppN2 or the ppHe in the loop? these are used for the decompression algorithm. The O2 gets metabolized and the other gasses dissolve in our tissue at different rates. For example when we decent to say 100ft the ADV kicks in to maintain our lung vol. lets say the dill tank is filled with 18/50. and for simplicity lets imagine the initial loop contents is close to 18/50 (freshly flushed with dill). So then our solenoid kick in (eCCR) to bring the ppO2 to a setpoint (say 1.3). Of course while the solenoid is kicking in we may need to vent some gas from the loop to maintain our neutral buoyancy at the same time we are breathing and both He and the N2 are getting diffuse into our tissue but at different rates. You can see that keeping track of the exact fraction of each gas other gas in the loop would be challenging. so unless the computer knows the loop/lung vol and the rate of diffusion of each gas at each depth, how does it know the exact N2 or He fraction in the loop? it doesn't, does it? but how does the estimate the FN2 and FHe. does it just base on the dil fraction 0.32 for N2 and 0.5 for He? I know it might not be very important in the grand scheme of things specially when we are dealing with models that are imperial /theoretical and not exact science. But one manufacturer of rebreathers claims to be able to estimate the ppO2 in the loop using a He sensor. Is this possible? It seems interesting
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Originally Posted by Capt Morgan
