Breathing the gas from your BCD

[TrimixToo]

A hypothetical scenario where I might recycle the breaths inside my BCD to try to save my life would be going deep inside a deep wreck on a single AL80, getting lost and draining the tank. With no other option I'd recycle the air in my bcd until I either found my way out and surfaced, ran into an alternate air source such as another diver, or passed out and drowned.

Enter a hard overhead environment on a single tank *and* not run a line? On purpose?

 

[TrimixToo]

The study addressed all of that when it was concluded that 13 breaths can be recycled.

Not "a couple".

I'd like to read it. Can you provide a link?

 

[boulderjohn]

Enter a hard overhead environment on a single tank *and* not run a line? On purpose?

Correct. In order to get into a situation where breathing from your (nearly empty if you are properly weighted) BCD makes sense requires that you start by doing something remarkably stupid.

If I am single tank diving with an AL80, I doubt I could get much of any breath out of the BCD.

 

[TrimixToo]

Correct. In order to get into a situation where breathing from your (nearly empty if you are properly weighted) BCD makes sense requires that you start by doing something remarkably stupid.

I can imagine an emergency that doesn't require stupidity. Entanglement in, say, PowerPro* offshore just before ascent from a deco dive causing a larger obligation and depleting back gas quickly, for example. Or entanglement in wires inside a wreck prolonging one's dive with the same effective result.

It is an interesting thought experiment (to me) to think about stretching the gas supply by using a wing as a counterlung for *n* breaths before exhaling into the water and getting a fresh breath of gas in that sort of circumstance. I'd certainly try it if I thought I had to, but I've been very careful and pretty lucky (I got tangled in the PowerPro at the *beginning* of the dive). It's also interesting to think about whether one would be better off doing that than by blowing off the deepest stop or two to make the first deco gas breathable. If it's a reasonable strategy, the optimum value of *n* would be very interesting.

* PowerPro is an offshore fishing line. It's an extremely strong aramid fiber, and drapes much more than regular monofilament, but it is fortunately easy to cut. Unfortunately, it's about exactly the color of a wreck that's been in the water for a long time, making it very hard to see, and there tends to be quite a lot of it if there is any at all because it's nearly completely limp and gets entangled in debris easily. Once you're caught in it, rolling over to see what you're caught on just entangles you more. Lovely stuff. If you fish with it.

 

[DanBMW]

Here in our Egypt Red Sea liveaboard during a briefing we were told that the upcoming dive would be from zodiacs and we were to do a negative entry, all splashing at the same time so we don't end up on top of each other, and meet up below the boat.

Then he says to make sure you're negatively buoyant breathe all the gas out of your BCD.

It's always been my understanding that breathing this gas is extremely dangerous and I've read one account of someone dying a horrible death from a bacterial lung infection.

I questioned the advice and the DM had no clue what I was talking about.

DON'T ! Never a good idea. Unless it's all the air available and the alternative is dying.

 

[johndiver999]

I can imagine an emergency that doesn't require stupidity. Entanglement in, say, PowerPro* offshore just before ascent from a deco dive causing a larger obligation and depleting back gas quickly, for example. Or entanglement in wires inside a wreck prolonging one's dive with the same effective result.

It is an interesting thought experiment (to me) to think about stretching the gas supply by using a wing as a counterlung for *n* breaths before exhaling into the water and getting a fresh breath of gas in that sort of circumstance. I'd certainly try it if I thought I had to, but I've been very careful and pretty lucky (I got tangled in the PowerPro at the *beginning* of the dive). It's also interesting to think about whether one would be better off doing that than by blowing off the deepest stop or two to make the first deco gas breathable. If it's a reasonable strategy, the optimum value of *n* would be very interesting.

* PowerPro is an offshore fishing line. It's an extremely strong aramid fiber, and drapes much more than regular monofilament, but it is fortunately easy to cut. Unfortunately, it's about exactly the color of a wreck that's been in the water for a long time, making it very hard to see, and there tends to be quite a lot of it if there is any at all because it's nearly completely limp and gets entangled in debris easily. Once you're caught in it, rolling over to see what you're caught on just entangles you more. Lovely stuff. If you fish with it.

I completely agree with you, there are so many situations where you can find yourself with little or no gas and deep.

So many people seem to think this will never happen so they don’t really think about it or guess that they can do a free ascent from 100 feet while they have never even tried one from 50 or 60.

I’m not a big proponent of rebreathing into a bc bladder and recycling air, but my regular buddy swears that it saved his life.

His circumstances were solo diving and sipping air and skip breathing and sitting on the bottom while heavy as he was trying to capture small tropical fish. You want to minimize the bubbles and noise so you inhale very slowly and hold inhalations and exhale very gently. With this technique, you can suck a tank to a very low pressure before feeling resistance and once you do, there is very little left if you have a good balanced regulator.

It scared him so bad he immediately bought a pony bottle and always carries it with him now.

The benefits of this technique are not theoretical, but I doubt most recreational divers have the discipline to do it effectively. I have never tried it, but occasionally practice swimming up while just exhaling (CESA ) when I have time to play around in moderate depths.

 

[TrimixToo]

I completely agree with you, there are so many situations where you can find yourself with little or no gas and deep.

So many people seem to think this will never happen so they don’t really think about it or guess that they can do a free ascent from 100 feet while they have never even tried one from 50 or 60.

I’m not a big proponent of rebreathing into a bc bladder and recycling air, but my regular buddy swears that it saved his life.

His circumstances were solo diving and sipping air and skip breathing and sitting on the bottom while heavy as he was trying to capture small tropical fish. You want to minimize the bubbles and noise so you inhale very slowly and hold inhalations and exhale very gently. With this technique, you can suck a tank to a very low pressure before feeling resistance and once you do, there is very little left if you have a good balanced regulator.

It scared him so bad he immediately bought a pony bottle and always carries it with him now.

The benefits of this technique are not theoretical, but I doubt most recreational divers have the discipline to do it effectively. I have never tried it, but occasionally practice swimming up while just exhaling (CESA ) when I have time to play around in moderate depths.

To be clear, it would require exceptional stupidity or exceptional circumstances for this ever to be a good idea on a recreational dive or even a technical dive. However, technical diving is sometimes about running the alternatives until none are left if the need arises. Knowing about more of them, and when they might be a good idea, isn't a bad thing. People die from omitted deco in emergencies just about every year, so many of us regard a deco obligation as a "hard" overhead environment.

Hence my interest in potential values of *n* and other alternatives, such as skipping the deepest stop or two, and which might be preferable. (Note that I do not mean so-called "deep stops," but those shown as needed running on modern dive computers running Buhlmann with GFs.) It's sort of like my interest in in-water recompression (IWR); I plan to never need it but an ace up my sleeve is never a bad thing if things go pear-shaped.

Remember how often the average recreational diver gets wet. It's usually a couple of times a year or less. In open water on any recreational dive with no deco obligation and the ability to achieve positive buoyancy however you can, a CESA is the way to go in my opinion. I've done them from 50-60' for practice. "Blow and go" was the phrase I was taught during initial training in the 70's. I've never done one from 130' but though I'd certainly break the "ascent speed limit" as I did on my practice ones, I am confident I could make the surface with plenty of time to spare. I might get bent but I'd be alive and (likely) treatable despite the very rapid ascent. I suspect no other option provides a better chance of survival. It's simple. It requires no new skills and no in-flight math. Just blow...and go.

 

[Blackcrusader]

To be clear, it would require exceptional stupidity or exceptional circumstances for this ever to be a good idea on a recreational dive or even a technical dive.

A bold claim. I have seen an OOA situation where a first stage got blocked when a diver went vertical head down and crap inside the tank blocked the first stage. I own my own gear and clean my own bladder. I've been trained for this technique by my BSAC / Commercial diving instructor in the 1980's. Always remembered this for being able to save my own life. An untrained diver may die having air in their BCD but me, I'm selfish and would rather live. Also you can keep the gas inside the BCD and use that for a controlled buoyancy ascent so you do not have to struggle to fin to the surface. BSAC teaches CBA in sports diving. I have mentioned it on this forum and understand some people are not for approving of this being discussed even.

One should not rubbish a live saving last resort if you have 3 mins TTS to surface and got separated from a buddy in down currents and had gear failure or an AOO situation. Having air in the BCD can be enough to safely get you to the surface. I'd rather risk a lung infection that can be cured that a drowning that cannot.

Technical divers have died near the surface because they forgot to open the oxygen gas for the CCR. Shouldn't happen to these experienced divers you will tell me. Try doing a CESA from 35m recreational depth. Not me, I use my BCD.

I do the rebreathing from my BCD a few dives a year with a good buddy if mine. reviewing and training is always a good thing. So is cleaning your BCD bladder.

 

[Blackcrusader]

I completely agree with you, there are so many situations where you can find yourself with little or no gas and deep.

The benefits of this technique are not theoretical, but I doubt most recreational divers have the discipline to do it effectively. I have never tried it, but occasionally practice swimming up while just exhaling (CESA ) when I have time to play around in moderate depths.

Hard to advise people to do something they are not trained for. I know several instructors that teach this outside of courses to more experienced divers now. They thought I was nuts when I told them but over the years they have come around to say... look it is an important tool to have in your kit in an extreme emergency. I end many dives with 100 bar but I'm weighted to be able to maintain safety stop depth in swirling water with 30 bar. So you might say he is overweighted... well I'm not. But it can mean if I am at 35m I have some air in my BCD already that could come in very handy if an emergency incident took place.

Also OW divers train to use the oral inflation of a BCD underwater. You just need to remember to exhale back into the BCD do no expel the gas out to water. Two reasons, buoyancy will change if you expel the gas and you will have less gas to re-breathe.

 

[Blackcrusader]

I've never done one from 130' but though I'd certainly break the "ascent speed limit" as I did on my practice ones, I am confident I could make the surface with plenty of time to spare. I might get bent but I'd be alive and (likely) treatable despite the very rapid ascent. I suspect no other option provides a better chance of survival. It's simple. It requires no new skills and no in-flight math. Just blow...and go.

You suspecting there is no other option means you are guessing.

I'll take my BCD which will have air in it from 40m and you do the CESA. We see who is relaxed and comfortable after riding the BCD to the surface over the one finning like crazy with no air trying to do a 5tts in 3 mins. Good luck.