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Thread: Surface offgassing into an O2 breather

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    RBW Member Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan is just really nice Padowan's Avatar
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    Surface offgassing into an O2 breather

    OK, here's the scenario - you're sitting at home wherever, not been diving lately, and breathing air - your body is in equilibrium with the atmosphere, ie. 0.79bar PPN2, and 0.21bar PPO2. You start breathing an O2 CCR, it'll take a few flushes to get the loop (your lungs and the breather) all containing 100% O2. But once you have reached this point, you now have a loop at 1bar PPO2, Zero PPN2, and your body at 0.79bar PPN2, so theoretically you would start offgassing the surface Nitrogen into the loop.

    My questions are these:
    1. Does anyone see anything fundamentally wrong with this as a principle?
    2. If this offgassing does take place, and the nitrogen you have in your body starts to enter the loop, the PPO2 will drop. Therefore as you metabolose O2, offgas N2 and the CO2 gets scrubbed, what will happen to the loop volume, I'm assuming it will drop, (ie, Metabolism + Scrubbed CO2 is greater than the offgassed N2)?
    3. Finally if the PPO2 continues to drop as the N2 enters the loop, the loop *could* go hypoxic - so does all this happen within the sort of timeframe that people are advised to flush and prebreathe an O2 breather?

  2. #2
    The 4th King Skeletor will become famous soon enough Skeletor will become famous soon enough Skeletor will become famous soon enough Skeletor will become famous soon enough Skeletor's Avatar
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    You have far too much spare time on your hands :D ;) :D

  3. #3
    Quote Originally Posted by Padowan
    My questions are these:
    1. Does anyone see anything fundamentally wrong with this as a principle?
    2. If this offgassing does take place, and the nitrogen you have in your body starts to enter the loop, the PPO2 will drop. Therefore as you metabolose O2, offgas N2 and the CO2 gets scrubbed, what will happen to the loop volume, I'm assuming it will drop, (ie, Metabolism + Scrubbed CO2 is greater than the offgassed N2)?
    3. Finally if the PPO2 continues to drop as the N2 enters the loop, the loop *could* go hypoxic - so does all this happen within the sort of timeframe that people are advised to flush and prebreathe an O2 breather?
    1. Nothing wrong except that offgassing is very slow as the pressure differential is low. Same goes for prebreathing O2 before a dive - you have to be on it for a long time to have an deco advantage. You are better off taking a aeroplane trip to dump N2.

    2. The ppO2 will drop so will loop volume.

    3. Your body doesn't contain enough dissolved nitrogen to replace the tidal volume of O2. You'd bottom out the CL before the loop went hypoxic. If you started out with an empty CL and a lungfull of air you'd pretty soon go hypoxic but provided you emptied your lungs first and breathed in from a full O2 RB then you won't die. I've done this loads of time for real.

    I wish I had a more interesting job then I spend less time here answering questions to people who are just as bored as I am.

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