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On Tue, 18 Apr 1995 DeepTek@ao*.co* wrote: > Richard's right about O2 tolerance. Due to the dynamic physiology of oxygen > toxicity what may work for you on one day may not work for you on another. It > may be possible to breathe Nitrox50 at 150feet (46 m) and survive 5 out of 6 > times (ppO2 2.7ATA). I don't plan on finding out, however. I do know of a > diver, though, that convulsed at 280fsw (86 m) breathing air (ppO2 1.9ATA). I > also know, thanks to Boyles Law, that the gas in my lungs will expand as I > ascend -- making controlled ESEs possible. And even if I don't quite make it > all the way to the 70 ft. (22 m) depth necessary to safely breath EANx50 > before I have to take a breath, A controlled-ESE (non-breath-hold) will at > least minimize the chances for an O2 hit by getting me closer to the mark. Err... What's an "ESE"? From the context I understand the meaning, but I can't figure out what the "ESE" stands for. Perhaps I'm not especially skilled at performing controlled ascents while venting gas out of my lungs, but whenever I've tried this in real emergencies, it never seems to work as well as well as they told me it would in dive school. An alternative that can buy you a few extra seconds on an ascent is to rebreathe off of your BC. I'd be dead now if I hadn't done this one one particular occassion. It's not as useful as most people might think - only about 4 or 5 breaths before the hypercapnia symptoms kick in. If you've got a fair volume of gas in the BC already, I'd recommend you perform an ESE as long as you can (inevitably you will vent gas off faster than Boyle's law expands it), exhale from your lungs all the way, then inhale from the BC. This allows you to dump a lot of CO2 that would cause problems if you were to simply ehale straing into the BC. I suppose you could also rebreathe off your drysuit in a life-or-death situation, unless you use argon...or don't have an off-board dumping system for "expendables". > Neither drowning, convulsing, nor embolizing sounds like good contingency > planning to me, though. More thought about what could cause a deep, > out-of-air emergency and how to prevent it or plan for it is a better > solution than either ESEs or bailing out on EANx50 at 150 fsw. Fully agreed. I should point out, though, that while good redundancy systems accomodate all conceivable single-point failures, virtually NONE accomodate all conceivable double failures. Thus, no matter how good your contingency planning is, the possibility of a life or death situation still exists. Knowing the relative risks of different non-ideal alternative bailout options can save a life. Aloha, Rich ******************************************************************* Richard Pyle deepreef@bi*.bi*.ha*.or* "WHATEVER happens to you when you willingly go underwater is COMPLETELY and ENTIRELY your own responsibility! If you cannot accept this responsibility, stay out of the water!" *******************************************************************
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