Can a BC be used as a rebreather in an emergency?

If you are at say 90 feet and have to do an emergency assent - you are just out of air and no one is around - go for it. Any gas is better then water and hurt on the surface I can do something about - dead on the bottom is only a body recovery.

Do not try to breath into a BC - you just don't have to.

If you had say 8 pounds of lift at 90 feet when you start heading up in your BC, you have a bit over 1 gallon or just about 4 liters of gas volume. As you ascend that volume will expand - you should do the math P1 x V1 = P2 x V2

But for ease of this example, lets say it will expand 3 time by the time you reach the surface. So, you will need to vent at least 2 gallons or 7 liters of gas from your BC. All you are doing is venting some of this amount through your mouth and out your nose. As for O2% - remember, you are not breathing into the BC as you are venting from the BC and the O2% will always be the same as what you had in your tank.

Last, remember in an emergency assent you are not doing 30 or 60 feet per minute - you will be doing 120 to 200+ feet a minute.

Someone will also probably bring up the possibility of a lung infection from any critters in the BC's bag - So what - infected on the surface is still much better then dead on the bottom.

 

Here is the Submarine escape suit - no bottle, no special gasses; just the 21% air in the sub. The suit keeps an air bubble around your head. In sport diving the air bubble is in your BC.

 

If you figure that each time your breath in and then exhale, you use up 4% of the O2 available, so given that there is 21% oxygen in the air that you breath, once you breath in and then exhale, you are putting 17% O2 back into the BC, now on the second breath, you breath in 17% O2 and again exhale using the 4% oxygen, now your down too 13%, by the second breath, you do not have enough O2 to survive on for very long at all, maybe just a mere second. Plan your dive then you will not have the need for such drastic measures and if it comes too it, a CESA is probably the best option.

 

I'd played around with it during pool dives as a DM in traning while waiting for instructor and students to come in the water.
But, IMHO, don't practise it often as your BCD might contain loads of crap that you might not want inside your lungs - if you cleaned your bcd bad etc.

But I'm no doctor..

 

I've breathed off my B.C. inflator hose during pool sessions before. It's definitely a skill that would need to be practiced regularly before used in an openwater emergency (and as another poster noted, lots of stuff can grow in the nice, warm, moist interior of a B.C. between dives, so take that into consideration). I have a few older textbooks that explain the technique.

If diving in less than 60 feet, I would try to go for a buddy's octo or pony bottle, or make an emergency swimming ascent before trying to breathe off my B.C. While it's possible to make an ascent breathing from your B.C., it's low on my list of options, and it's not something I practice regularly enough to feel proficient at.

 

Interesting to note... the ol' Fenzys were set up the same way... and, at least according to their web site... the NEW Fenzy BC (military) actually is set up to allow you to breath off the oral inflate tube without having to push buttons...

 

We used to practice this methos with 'Fenzy's' in the 70's and I aint sure but I think the thing was breath in, breath back into Fenzy, add air from bottle and flush, breath again.

Never tried anything more than practice but I didnt die from a lung infection. Just lucky I guess.

 

I'm thinking if you're to the point where breathing whatever air is in your bcd is an option, Murphy is in charge of the situation not you.
When Murphy is in charge, things tend to get exponentially worse by the second.

Think about it, how many things have gone wrong to make this an option?
You're OOA, NO Buddy to share air, too deep to ESA

But if its the only option you think you have, like others have said,
Better to be hurt on the surface than dead on the bottom.

 

Is this a hypothetical question, or something you are actually contemplating?

If this is something you are actually contemplating, my suggestion is to find a buddy, or dive doubles, or get a pony! Take your pick, they are provide redundant air in the case of an emergency.

 

This was taught in my SSI class in 1983. I use to practice it using rental BCs in the 80s. I never had an issue with an infection.