CESA Question

[boulderjohn]

In CMAS training we used to train students performing a CONTROLLED buoyant ascent, not swimming at all, but playing with the BCD for ascending at a reasonable speed. They even had to stop at 3m, where the deco bar was hanging from the boat, and additional tanks were waiting. The exercise was planned to be conducted from 15 meters depth, at the end of an instructional dive, and followed by a 5-minutes safety stop at the deco bar.
After a few years this exercise was removed from the syllabus, as it was considered dangerous. For the instructor, not for the student, as the instructor had to ascend together with the student and had to repeat this ascent with each student on the group (usually 4), causing a significant risk due to the repetitive up-down profile.

That is nearly what is done today, and it is controversial for the same reason. In a CESA, the student should begin the ascent neutrally buoyant, as would happen on a real dive. During the ascent, the BCD will expand, and the student is taught to dump air a little at a time as that happens so that the ascent remains under control.

The issue of multiple ascents for the instructor is very much still in play. Years ago PADI identified a specific dive on which the CESAs were to be done, but PADI now allows the instructor to spread them over the entire set of dives to limit the number of ascents on one dive.

When people talk about this, they often talk about that as if the CESA were the only ascent going on. There are other ascents, though, and in instructor will be yoyoing quite a bit during the OW class even with the CESAs spread out. Let's say, for example, that the instructor has a class of 8 students, and he decides to do 2 CESA's on dive #2. The instructor also has to ascend 4 times (once each for each buddy team) doing an OOA. Then the instructor has to ascend with the class at the end of the dive. That's a total of 7 ascents on that dive.

 

[Superman541]

Here is what I appreciate today: The numerous and prompt replies, the very helpful information and guidance, and the gracious congratulations and well-wishes. Oh....and the inherent dangers of this sport and the importance of continuous learning and attention to safety principles and procedures.

 

[boulderjohn]

On the way up, he discovered that one extra breath does indeed become available as the no-longer-compressed gas in the cylinder expands during the ascent.

While more air does indeed become available to the student upon ascent, it is not because the air in the tank is expanding. Air in an inflexible container is not affected by pressure.

The regulator is designed to deliver air from the tank to the second stage at roughly 140 PSI above ambient pressure. As pressure drops, the diver will feel it become harder to breathe, and then there will not be enough pressure coming from the tank for the regulator to function--but there will still be some pressure. As the diver ascends, ambient pressure drops, and at some point the remaining air in the tank will be providing enough pressure for the regulator to work again.

 

[boulderjohn]

While more air does indeed become available to the student upon ascent, it is not because the air in the tank is expanding. Air in an inflexible container is not affected by pressure.

The regulator is designed to deliver air from the tank to the second stage at roughly 140 PSI above ambient pressure. As pressure drops, the diver will feel it become harder to breathe, and then there will not be enough pressure coming from the tank for the regulator to function--but there will still be some pressure. As the diver ascends, ambient pressure drops, and at some point the remaining air in the tank will be providing enough pressure for the regulator to work again.

BTW, this is one of my peeves about the way CESA is taught. The instructional methodology involved is simply wrong from an instructional theory point of view in many ways. This is one of them.

Yes, in an OOA situation, you will indeed be able to take an additional breath (and likely more) upon ascent. In fact, if you start the ascent immediately upon feeling the harder breaths from the emptying tank, you should be able to do a normal, breathing ascent all the way to the surface.

But we don't teach that. Unless the student has an instructor (like me) who explains this, the student will not know that air will be available upon ascent in an OOA situation. In fact, if a student expels air too quickly and inhales a few feet from the surface, the student has failed the exercise and must repeat it. In proper instruction, the student will know air will be available, will demonstrate that knowledge by taking a breath near the surface, and be rewarded for it.

So why don't we do it that way? I actually asked headquarters, and they explained that what I said is only true in an OOA emergency. If for some incredibly unusual reason the regulator had simply failed, the student would not get air. Therefore, we don't mention it, and we don't allow the student to take a breath of air. Thus, when we teach the CESA, we are not teaching how to deal with an OOA emergency--we are teaching what to do in an unnameable emergency causing the regulator to fail.

What are the consequences? A joint PADI/DAN study about a decade ago found that the most common cause of an accident-related scuba fatality was an air embolism following a rapid, panicked ascent to the surface following an OOA incident. In those case, the divers almost certainly held their breaths, believing they could not get that far exhaling all the way, and not knowing more air would be available of they were to inhale at almost any point.

 

[boulderjohn]

The old days when J-valves with no SPGs were common were before my time, but apparently malfunctions were common enough with them to make CESAs common. About a decade ago, in one of the many threads on topics like this, a participant talked about a potential one regulator buddy breathing scenario at 100 feet by declaring that there is no way he would share his air with someone. An old timer instructor (Thalassamania) replied that if he were in that situation with that guy who would refuse to share air, he would calmly give him the entire BCD, tank, and regulator and then ascend next to him doing a CESA, blowing bubbles at him the whole way.

So even though I have not practiced a CEA from great depths, I have total confidence that I can get safely to the surface without too much trouble, which sadly contrasts with the divers who die after a panicked, breath-holding ascent.

 

[Scraps]

Boulder John,
That’s helpful insight and info.
Thanks!

 

[TMHeimer]

In addition to what I wrote above....

The navies of the world have used buoyant ascents for submarine escapes since the early 1950s. A Google search will find navy films showing it. The older ones are better because the escape is done with nothing but a very primitive BCD rather than the special suits used now. The students are taught to exhale fully before starting the ascent, and then continue to ascend the entire way up. This has been done from 300 feet.

Yes. I've often read here that people have done CESA from very deep-- like 100'. When I did my AOW I asked the instructor what do you do if you are below 30' and thus can't do a CESA (I didn't know it was a suggestion..). He said "You do one anyway".

 

[boulderjohn]

Yes. I've often read here that people have done CESA from very deep-- like 100'. When I did my AOW I asked the instructor what do you do if you are below 30' and thus can't do a CESA (I didn't know it was a suggestion..). He said "You do one anyway".

I wrote to PADI about this, too. They told me that the dividing line between CESA and buoyant ascent was really your judgment.

Yes, there were scuba training groups whose graduation exercise was a CESA from 100 feet with the regulators out of their mouths. (Don't do that!)

 

[Boarderguy]

Welcome to diving! You've got a great deal of outstanding diving in your backyard. Enjoy the warm water and pretty fish on your trip and then come right back to blowing bubbles in the sound. Bookface has a lot of local groups and there are dives planned weekly from Seattle to Hoodsport. This little guy joined me out in West Seattle.

 

[wetb4igetinthewater]

This little guy joined me out in West Seattle.

Someone needs to teach that guy to frog kick to stop stirring up the silt!