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At 06:27 AM 4/21/01 -0700, you wrote: >Hans, > >Does this mean the following senario would be bad: >1. You're on deco from a trimix dive on 50/50. >2. "Something" happens and you can't use 50/50 so you >switch to your back gas (trimix). > >Would that be "bad"? > >-ben In theory it might be but all practice has shown it's no problem. As I said, counter diffusion problems are rare. The steady state problems take place if you're in a chamber heliox atmosphere and breathe a heavier gas (neon or nitrogen) and keep this imbalance up for a long time. The manifestation is a kind of skin bends. Argon for suit inflation is the opposite -- the "slow" gas surrounds you while you breathe the "fast" one. Backgas switching to helium during deco evidently works fine and I do it myself. However, in theory this is the kind of switch that will raise the tension of inert gas for a moment. Since the general trend during deco is to move up towards less helium and more oxygen this transient surge of helium probably doesn't matter. Moreover, if you've been on 50/50 for some minutes, not to say oxygen, your blood is depleted of inert gas and there's "room for" that transient influx of helium. The steady state imbalance is the one you won't get away from since this imbalance is aggravated with time rather than evening out. The only practical concern is that occupants of a hyperbaric chamber should be in the same kind of atmosphere as the gas they're breathing, as inert gases are concerned. You can always breathe a higher FO2 gas. Hans -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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