CESA Question

[johndiver999]

I just meant that as soon as you start re-breathing from a wing, you start a clock counting down with a matter of a few minutes to both hypercapnia and hypoxia. Hypercapnia leads to hyperventilation, panic, and then loss of consciousness, with increased rate of breathing happening pretty soon in the process. Hypoxia simply leads to loss of consciousness with little warning. Once consciousness is lost, drowning typically follows. If the diver ascends to the surface quickly enough, say at the same rate as in normal CESA, then there's probably not enough time for full hypercapnia/hypoxia to set in, so I concede that point, but what if the diver ascends a little more slowly because they now have the sensation of being able to breathe, taking two minutes to reach the surface? Anyway, if they black out, it's very very bad.

I forgot to mention another reason this procedure is a bad idea. It's pretty easy for some water to enter the inflator hose (and wing) during a dive. So if you are contemplating taking a breath from an inflator hose, you must remember to first purge the hose by somehow venting gas through it, or you risk inspiring water at the worst possible time. Coughing would be bad, at this point in the process. If you were running with the wing close to empty during the normal portion of the dive, there is likely water in the inflator mechanism, and at the same time not enough air to purge the hose completely. If there is water in the wing, then being slightly heads-down could bring that water forward and into the inflator hose. Starting to sound like a lot to keep track of, for someone who is calmly facing their own mortality?

If you were going to do this, you would exhale into the BC. You would be ascending vertically and presumably kicking. In the upright position, any water in the BC will fall to the bottom of the BC and inhalation off the inflator will release air - not water - the same as every other time you vent the BC in a vertical position.

I personally expect that if I were forced to make a real emergency ascent with no air source, I would drop everything (except a scooter if it were working) and just swim like my life depended on it. I'm not sure I would have the presence of mind to use the BC to recycle my exhalation. I never tried it as a drill.

 

[boulderjohn]

I personally expect that if I were forced to make a real emergency ascent with no air source, I would drop everything (except a scooter if it were working) and just swim like my life depended on it. I'm not sure I would have the presence of mind to use the BC to recycle my exhalation. I never tried it as a drill.

I wrote about this repeatedly earlier in the thread.

The US and British navies have been teaching submarine escapes sine the 1950s. If you seek out some of the earliest films from that era, it will be a revelation to you. They wore what was essentially a small snorkel vest, and they followed this procedure, and they did it from as deep as 300 feet.

1. Step One: Exhale fully
2. Step Two: Begin swimming upward.
3. Step Three: Exhale all the way to the surface.

That's it. That's all there is to it. There is absolutely, positively no reason to be messing with breathing in and out of a BCD. It's that kind of screwing around with a simple process that will get you killed.

Once again, please note: the first step is to exhale fully, then ascend, then continue to exhale as you go.

 

[Bob DBF]

The US and British navies have been teaching submarine escapes sine the 1950s. If you seek out some of the earliest films from that era, it will be a revelation to you. They wore what was essentially a small snorkel vest, and they followed this procedure, and they did it from as deep as 300 feet.

1. Step One: Exhale fully
2. Step Two: Begin swimming upward.
3. Step Three: Exhale all the way to the surface.

That's it. That's all there is to it. There is absolutely, positively no reason to be messing with breathing in and out of a BCD. It's that kind of screwing around with a simple process that will get you killed.

The big difference is that submarine escape is a buoyant ascent, and is more fun than keeping ones ascent less than 60 fpm, although the basic principles are the same. The buoyant ascent, in scuba, is next level of emergency procedure after the CSEA, and normally reserved for situations where one is screwed, and being on the surface as fast as possible is the only solution. The two different procedures are somehow conflated in divers minds today, which was not the case when I started diving.

And I might add, that the submarine buoyant ascent has been done from over 600', the following link is an account of that test escape. Submarine escape from 603 feet. The trick on the escape is to pressurize to depth as fast as possible to minimize ongassing nitrogen, essentially giving no, or minimal, bottom time, or as we say, a bounce dive.

 

[boulderjohn]

The big difference is that submarine escape is a buoyant ascent, and is more fun than keeping ones ascent less than 60 fpm, although the basic principles are the same. The buoyant ascent, in scuba, is next level of emergency procedure after the CSEA, and normally reserved for situations where one is screwed, and being on the surface as fast as possible is the only solution. The two different procedures are somehow conflated in divers minds today, which was not the case when I started diving.

And I might add, that the submarine buoyant ascent has been done from over 600', the following link is an account of that test escape. Submarine escape from 603 feet. The trick on the escape is to pressurize to depth as fast as possible to minimize ongassing nitrogen, essentially giving no, or minimal, bottom time, or as we say, a bounce dive.

Yes, but there is barely a difference. If you don't feel confident you can get to the surface with a CESA, you do a buoyant ascent. The only difference is that in a buoyant ascent, you don't take steps (like dumping air from the BCD) to slow yourself down.

 

[Bob DBF]

Yes, but there is barely a difference. If you don't feel confident you can get to the surface with a CESA, you do a buoyant ascent. The only difference is that in a buoyant ascent, you don't take steps (like dumping air from the BCD) to slow yourself down.

That is because the understanding, training and practice of CSEA is non-existent in scuba training today. Prior to widespread use of the SPG, when using a j-valve, a CSEA was necessary if the valve was out of position, not a completely uncommon occurrence. With a K-valve, a CSEA it was normal until one got could guage their gas usage by time. I did a lot of CESAs in the beginning, but it was the same as a normal ascent, except I was a bit sparse on air. The point being, after one gets used to the procedure, it is no longer traumatic, same as a trip in the submarine escape tower. Fear kills, that's why one trains.

At 60 fpm it's one minute to the surface from 60' and air is available as one ascends. 60 fpm was the normal ascent rate at the time, and is still the acceptable limit now, although 30 fpm is now the preferred normal ascent rate.

 

[boulderjohn]

That is because the understanding, training and practice of CSEA is non-existent in scuba training today. Prior to widespread use of the SPG, when using a j-valve, a CSEA was necessary if the valve was out of position, not a completely uncommon occurrence. With a K-valve, a CSEA it was normal until one got could guage their gas usage by time. I did a lot of CESAs in the beginning, but it was the same as a normal ascent, except I was a bit sparse on air. The point being, after one gets used to the procedure, it is no longer traumatic, same as a trip in the submarine escape tower. Fear kills, that's why one trains.

At 60 fpm it's one minute to the surface from 60' and air is available as one ascends. 60 fpm was the normal ascent rate at the time, and is still the acceptable now, although 30 fpm is now the preferred normal ascent rate.

I agree, and I think a big part of the problem is that at least 90% of the current crop of instructors came of age in the more modern era and really don't understand all of this. That was true of me when I became an instructor about 20 years ago. It took several years of learning about this stuff on my own before I realized we did a crappy job teaching it because we don't understand it. The fact that we do a crappy job teaching it can be seen by the frequency with which threads like this appear on ScubaBoard.