slackercruster
Contributor
If so, will it get you up from 70 feet or so?
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The safer way would be to breath in and exhale through your nose, that way you are not rebreathing the gas from it. Now if your power inflator is working you could use it by depressing both buttons at the same time, I practice this technique a few time to see if I could do it and I didn't have too much trouble with it./QUOTE]
This is my understanding of the correct way to use a BC's oral inflator as a third option. Depress both buttons, take a breath, let go of the buttons, exhale through the nose or take the inflator out of your mouth and exhale into the water.
I have read anecdotes that the inside of a BC or wing acquires a lot of nasty stuff you do not want in your lungs unless it is the only way to survive an incident. I can't say for certain.
If you had enough gas in your BC for 5 or 6 breath sure you could use it. The safer way would be to breath in and exhale through your nose, that way you are not rebreathing the gas from it.
Yes a BC can be used as a rebreather, but it is a technique that must be practiced. It is dangerous. We used to practice this technique as a last resort in an out of air situation in an overhead environment. Let me repeat "IT IS DANGEROUS" The only reason to do this would be to get you that last 50 or so feet out to open water so you could do a blow and go. No other reason is worth the risk. For open water I would never attempt this from any depth. There is a great danger of shallow water black out in an ascent from 70 feet rebreathing gases from a BC.
I completely agree that it's dangerous, and that a CESA is less risky and probably easier, and that you might only contemplate this as an extreme last ditch matter. But as an intellectual exercise to understand what the limits are, anyone care to comment about my rationalization:
IIRC, over short periods of time, breathing gas doesn't start to become a consciousness limiting problem until O2 goes below roughly 10-12% and CO2 gets above 10%, although breathing starts to get uncomfortable around 5%. At the surface/1 ata, max CO2 output is about 4%. Since metabolic rate is independent of depth and therefore O2 consumption and CO2 exhalation are constant mass irrespective of depth, at 70 feet/3 ata, breathing output is only about 1.3% CO2, with a similar drop in O2 content. So you could theoretically recycle the same volume of air around 6-8 times before the gas composition was really beyond limits.