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At 11:53 AM 2/4/00 -0500, Robert Wood wrote: >Steve Schultz wrote: > > > > I think I know where this absolute bullshit is coming from. > > During my TDI Basic Nitrox course, they actually recommended carrying > > EAN39 as a bailout gas for MOD 130. "you'll only be breathing the mix for > > a few seconds until you can get to the proper depth". Actually, this may be correct -- the risk of a hit is low if you get up from 1.9 ASAP. However, the benefit of breathing a high PO2 for a few minutes is negligible as well. The good doctor seems to believe he gains a worthwhile deco benefit from spiking his bail-out. If so, we'd be in a real risk versus benefit situation. However (that's a fancy "but" again), a pony is way too small to provide enough gas for enough time to make the gradient work. A pony is good for getting out without inhaling water -- it's not good for deco. Now, if you carry a stage rather than a pony you'll get enough gas for a proper deco but then you won't have to spike the PO2 to get out on a rec or light tech dive in the first place. The idea of spiking the PO2 to make a pony suffice for deco doesn't work since you need time (blood turnover) as well as absence of inert gas to accelerate your deco. There's really no way to accelerate a deco within the capacity of a pony cylinder, in other words, a moot or a mute point :-) BTW, George is absolutely correct on the immersion effect -- don't you ever believe you can take a high PO2 underwater since you can take it in a dry chamber. The brain auto-regulates oxygen up to a PO2 of about 2.0 all right -- in the absence of CO2 stress and the presence of a normal gravitational pull on the blood circulation. Once submerged, the brain's auto-regulation is severely limited. Blood normally pooling in the legs is being "freed" and the ensuing hypervolemia will counter cerebral vasoconstriction. In plain English, the brain tries to choke down the blood supply while the high blood volume forces the arteries open. Result: far more oxygen than the brain wants! Conclusion: I wouldn't worry too much about 1.9 for 5 seconds but it won't do anything for my deco anyway so why risk it? regards, 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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