Breathing from BCD

[drdaddy]

No, I wouldn't do it for a number of reasons.

First, you should not find yourself OOA. There are some some remote possibilities of equipment failure, but for the most part, this is due almost entirely to diver inattention.

Second, you should not be diving without a buddy unless you have a redundant air source. If you are both OOA and OOB (Out of Buddy), you really need to work on your and your buddy's attention to safety.

Third, in most any OOA situation, there is still air in your tank that is not available due to ambient pressures. As you ascend, the pressure in the tank becomes greater than the ambient pressure and air will become available to you. Keeping your regulator in your mouth and your airway OPEN will facilitate you being able to breath off of this increasingly available air supply. Removing your reg to try to breathe off of your BC will flood the reg and require you to purge it before you try to breathe.

Fourth, when you are OOA, you don't need to mess with your buoyancy! You will find that when you are truly OOA, that you will want to exceed that Max 30fpm ascent rate you learned in class. The air in your BC expands as you ascend actually helping you to ascend. Is this dangerous? Not near as dangerous as your imminent drowning. Kick like hell and tear for that surface.

Finally, if you are properly weighted, you have very, very little air in your BC. I often dive with no exposure suit and with little to no air in my BC. There is NOTHING for me to breathe in there! If I just ran out of air, then I don't have anything to put in to start that cycle and I am wasting TIME rather than seeking that big alternate air source you call the surface!

In the beginning days of diving I dove with a J-valve and no SPG. When I eventually ran out of air, I normally pulled the rod which gave me more than enough air to ascend. More often than I liked, I would find the rod was already down. Since I had no concept of diving with a buddy at the time, the surface was my only hope. There are a few of those events still etched clearly in my mind, but the outcome was always the same: breathing that sweet, sweet air on the surface. However, since I started using an SPG, I have to brag that I have never, ever run out of air. Not once. Start your own tradition of not running out of air from this point forward!

Thank you for this very well put explanation.

The only time I was in real trouble and have a bit of PTSD which I have worked through, was on a dungeness crab dive. I just want to warn people about this.

My weight is perfect (I'm not talking about my belly ) and my buoyancy excellent. But when you have close to your limit of shellfish or ocean sized dungeness crab (3-5lbs each x12) in your game bag hooked in such a way it's not quickly releasable, you will come to the surface over-weighted. And being that I was down in the murky cold waters for 40 minutes at the change of tides, things can be very different when you come up. I lived and learned and will never be so cocky to put myself in such a position again. My life is not my own - I became a servant when I married and had children and my parents became aging and I also have psychiatric patients whose lives are sometime very dependent on my services/caring. I digress, because my life is very different than when I was a young single crazy guy diving the world and going to places that I am fortunate to be alive today. I never should have done that second dive that day - and I knew better.

But the point is, that there are times that your buoyancy may change and so may the surface conditions be much different than when you went down. Fish are more neutrally buoyant than shellfish!

And "No, I would breath out of a BCD" for all the reasons that NetDoc so wisely and concisely said.

Thank you again NetDoc.

 

[marcosdutra]

Do your best to stay alive, no matter what and how

 

[SeaHorse81]

If you are in the open water with the potential for a direct ascent to the surface, there is no need to do this.

You were taught how to do a CESA in your OW class--just start heading for the surface, exhaling slowly as you do and leaving your regulator in your mouth. If you exhale everything before you get to the surface, just inhale through your regulator. Your tank is not really out of air. The regulator could not deliver air to you at the pressure you were under when you drew that last breath. As you ascend to lesser ambient pressure, it will be able to give you a breath of air again, and you can start the CESA over again. The closer you get to the surface, the more air you will get this way.

In the absolute worst case scenario, you should still be able to get to the surface without breathing with the amount of O2 that is still in your blood.

This is the best articulation of why CESAs work that I have ever seen. I've seen/heard the idea expressed many times, but never quite this clearly.

Removing your reg to try to breathe off of your BC will flood the reg and require you to purge it before you try to breathe.

I've pondered the notion of breathing off the BC in dire circumstances -- this is the best argument I've seen against it, when combined with BoulderJohn's quote above.

Kick like hell and tear for that surface.

This one surprised me a bit, as I've always been admonished to surface with as much moderation as possible if having to do a CESA. As I thought about it more, I realized that a moderated CESA gets you to the surface what, maybe 10 seconds later than an all-out rush? That's not enough difference to matter for off-gassing, so seems not worth it. I'd certainly see the point of getting to the surface WITH PURPOSE but not with panic, since panic never helps.

There may be one point about exertion on the way up, however. The harder you exert yourself, the faster you deplete your oxygen supply and the sooner you absolutely have to take a breath, whether or not there's one available. Maybe this is the reason people say to not necessarily do the mad dash?

 

[GoodKarmaKid]

If you are in the open water with the potential for a direct ascent to the surface, there is no need to do this.

You were taught how to do a CESA in your OW class--just start heading for the surface, exhaling slowly as you do and leaving your regulator in your mouth. If you exhale everything before you get to the surface, just inhale through your regulator. Your tank is not really out of air. The regulator could not deliver air to you at the pressure you were under when you drew that last breath. As you ascend to lesser ambient pressure, it will be able to give you a breath of air again, and you can start the CESA over again. The closer you get to the surface, the more air you will get this way.

In the absolute worst case scenario, you should still be able to get to the surface without breathing with the amount of O2 that is still in your blood.

^^^^ THIS^^^^^^

Great simple explanation. This would be my preffered method at nearly all recreational depths. Unless your with a highly skilled buddy who is very close to you. Your going to spend more time, energy, and air getting to your buddy then it would to reach the surface safely where there is an unlimited supply

In my mind, there really is no excuse for being out of air, with the possible exception of equipment failure.

Jason

 

[Soggy_Diver]

Just as an experiment, I tried breathing off my BC, both on the bottom and ascending, in a deep pool (16 feet). Before trying this, I washed out the inside with listerine.

Here is what I learned:

I had to breath off of the BC very carefully, because of course the oral inflator was flooded.
At this depth, there was almost no air in the BC, so to make this drill work, I had to put on some extra weight and some extra air in the BC.
The BC (I tried this with my Sherwood Silhouette) leaked air around the oral inflate, so this was good only for about 6 breaths, about 1 minute max.
The feeling of air pressure coming out of the BC varied noticeably, depending on whether I was positioned so that the "bubble" in the BC was lower or higher than my lungs.
It was easy to control the buoyancy on the bottom, because my lungs and the BC formed a closed system with a constant volume of gas. On the ascent, I found it easy to control speed by inhaling from the BC, then exhaling enough through my nose to set the speed.

So, not a practical self-rescue method, but an interesting way to spend some winter pool time.

 

[Elvistheking]

Just out of curiosity, does anyone have any actual data to support the belief that BCDs are "usually very contaminated"? It's trivially easy to clean the inside of a BC, just like cleaning a camelback drinking bladder. Drop some vinegar in, swish around and rinse with fresh water. Dry as normal.

If, and this is a big if, someone rinses and drys their BC with a little air in it after each dive, there is no reason for it to be "contaminated" with anything particularly nasty at all.

Yep:
Diver Dies Following Lung Infection After Rebreathing BCD

 

[Elvistheking]

Just as an experiment, I tried breathing off my BC, both on the bottom and ascending, in a deep pool (16 feet). Before trying this, I washed out the inside with listerine.

Here is what I learned:

I had to breath off of the BC very carefully, because of course the oral inflator was flooded.
At this depth, there was almost no air in the BC, so to make this drill work, I had to put on some extra weight and some extra air in the BC.
The BC (I tried this with my Sherwood Silhouette) leaked air around the oral inflate, so this was good only for about 6 breaths, about 1 minute max.
The feeling of air pressure coming out of the BC varied noticeably, depending on whether I was positioned so that the "bubble" in the BC was lower or higher than my lungs.
It was easy to control the buoyancy on the bottom, because my lungs and the BC formed a closed system with a constant volume of gas. On the ascent, I found it easy to control speed by inhaling from the BC, then exhaling enough through my nose to set the speed.

So, not a practical self-rescue method, but an interesting way to spend some winter pool time.

Nice way to give yourself a CO2 hit!

 

[Soggy_Diver]

Nice way to give yourself a CO2 hit!

Probably should not happen in 1 minute, right? Otherwise, people would also get CO2 hits from simply breath holding for 1 minute at the same depth. Also, the CO2 that I would be producing is diffused between both the air in my lungs, and the air in the BC. So if we estimate that the volume of air in the BC is around 4 liters, and my lungs are around 4 liters, that would roughly cut the concentration in half.

Or am I missing something?

In any case, I do not want to recommend BC breathing to anyone.

 

[Elvistheking]

Probably should not happen in 1 minute, right? Otherwise, people would also get CO2 hits from simply breath holding for 1 minute at the same depth. Also, the CO2 that I would be producing is diffused between both the air in my lungs, and the air in the BC. So if we estimate that the volume of air in the BC is around 4 liters, and my lungs are around 4 liters, that would roughly cut the concentration in half.

Or am I missing something?

In any case, I do not want to recommend BC breathing to anyone.

Yep, because you'll be breathing in and out you'll slowly increase the fCO2 in the air with each breath faster than you would if you just didn't breath, which will make you want to breath more and so the air will have an increasingly higher fCO2 meanwhile the act of breathing produces even more CO2, this combined with the increased depth increased the ppCO2.

Hey if you felt no ill effects good for you, I personally like to avoid almost barfing underwater, the subsequent headache and feeling like crap for the next 1/2 hour at least that a CO2 hit gave me.

 

[Thalassamania]

BC breathing was developed for use with an ABLJ, to wit: a BC with a small tank of compressed air attached like a FENZY. It was abandoned when the Scottish Diver article came out detailing the lung infection concerns.