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I understand how O2 is metabolized but I did not realize that the BMD had no way to add O2. It obviously must add nitrox periodically to the counterlung. Sorry for the misunderstanding. Now my question is why would anyone want to buy such a limited use rebreather. It would be cheaper all around if you hired someone to ferry scuba bottles to you for your 2 hour dive. On Tue, 1 Aug 1995, Dave Schubert wrote: > Rod Farb wrote: > > > My problem with your scenario is that the > >student had problems with using air with the BMD rebreather and became > >hypoxic. My question is how come we breath air now and have no problems > >becoming hypoxic. How come open circuit divers don't become hypoxic > >breathing air. If you mean that the unit did not supply make-up O2 to the > >air that was being rebreathed when it went lower than 16% or so, then I > >would I would say that the "instructor" allowing the diver to use the > >unit in that fashion was an idiot and had no concept of the rebreather as > >life support.< > > The BMD rebreather is a nitrox or other single gas mix rebreather. > Therefore if air was added to the tanks there would be no other addition > mechanism to add any higher FO2 mix as in constant flow systems with 100% > FO2 and a diluent gas as well. > > Technically the reason this would happen is that with a BMD SCR-4 using a > mix of 21% O2 in the bottles the mix will start somewhere around 18% FO2 if > 4% O2 is used each breath and then drop with each breath until what > happens, did. This is because 25% of each exhalation is purged from the > system. The unit was designed to use nitrox mixes with higher FO2's so that > with the purging the FO2 would still come in above 21%. Doing the math, > it's averaging (assuming 4% used): > Breath 1: 21% > Breath 2: 1 part 21% from addition + 3 parts x > (.21-.04)=.69/4 parts=.18 FO2 > Breath 3: 1 part 21% from addition + 3 parts x > (.18-.04)=.63/4=.16 FO2 > Breath 4: 1 part 21% from addition + 3 parts x (.16-.04)=.14 FO2 > Breath 5: Etcetera > > This might all be a moot discussion, at least as it concerns the BMD > situation and their training. I tried calling them in Canada and all I > received were message machines moving me from one place to another. Does > anyone know if there are any humans left at BMD?-Dave > > >
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