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Something that's always been in the back of my head as a "just in case", and I got to thinking about it more seriously the other day after reading something related. Here's the hypothetical:
You're at depth, and since your wetsuit is compressed you need to add some air to your BC.
Suddenly, a shark comes and grabs your buddy and takes him away (so that we don't get into a "being a better buddy" discussion )
And so we don't get sidetracked into a "gas management" discussion , let's assume that just as suddenly your air supply stops due to some kind of failure of your first stage regulator, making both your regs dead. And you don't have time to realize there's still air in your tank and you can breathe directly off your tank valve.
So the only air at your disposal is in your BC. So here's the items for discussion: Do you treat your BC as a closed circuit rebreather (since there's still a lot of O2 in your exhale), and exhale back into the BC as you ascend? Do you have to worry about the increased partial pressure of CO2 causing you to go goofy? Or do you take a breath from the BC, then exhale into the water as you ascend?
And assuming that there's probably all kinds of mold and crud inside your BC, do you, as part of your normal BC maintenance, include a bit of disinfectant or something when you wash out your BC?
I suppose you could guesstimate how many CF of air are in the BC at depth, and figure out how long it might last...my guess is it ain't very much at all.
The master diver book I'm currently finishing up mentioned that serious (i.e. life-threatening) fungal lung infections can come from breathing from your BC. It went on to note that certain death is incurable, while hospitals may be able to cure an infection.
If I was too deep to make the surface, and assuming I had no other air (due to the shark having bitten my tank in half before chowing down on my buddy, God rest his soul... both halves, even), I would take one normal breath off the BC and make my emergency ascent (likely dropping my weights, as if that wasn't required, I could've done a "normal" CESA without the BC breath), and then I'd pray that Jaws didn't already chew a hole through the boat and eat all the people, because I'd really like them to get on the horn ASAP and give me the O2, already.
If you have enough air in your BCD at depth to do this, you may have other issues you need to take a look at...
Ummmmmm. Such as wearing a thick neoprene wetsuit? They DO compress, you know. Even if perfectly weighted, a diver with thick neoprene wetsuit at depth will have significant air in the BCD.
I would treat the BC as maybe one-half to one extra breath of air, which could be vital since you might find yourself without air supply on an exhaled breath. Most people can last 60 seconds on a full breath but much less on empty lungs.
You should be able to rebreathe at least once, maybe 2 or 3 times if using nitrox. But you need to vent for buoyancy control as you ascend anyway so I'd exhale into the water.
But I think I'd reach for the BC hose as a very last resort.
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Originally Posted by gangrel441
