Coroners Report. What do you think!

[Storker]

It is my understanding that there are no pain receptors in the alveoli.

Correct.

If so, how does a diver know how much air to vent on ascent (if keeping the airway open and actively venting air) is insufficient to prevent injury during an ascent made at a reasonable rate

Fully open glottis = generally no problem. You'd be hard pressed to ascend faster than the expanding gas exiting. Problem comes when people aren't able - or willing - to keep their glottis open enough. Just let the excess exit with no restrictions. Aaaahhhh.....

 

[Ken Kurtis]

Thanks for looking into it for me. It is my understanding that there are no pain receptors in the alveoli. If so, how does a diver know how much air to vent on ascent (if keeping the airway open and actively venting air) is insufficient to prevent injury during an ascent made at a reasonable rate?

You don't. And therein lies the rub. More is better.

And the reality is that if you REALLY ran out of air and had to do an actual CESA to save your life, it would in reality be a PESA: Panicked Emergency Swimming Ascent (disclaimer - I'm making a little joke with this moniker to make a point). So again, more is likely better and you won't know until you reach the surface whether it was enough or not. These ascents, whether in training or for real, are Pass/Fail. No grading on the curve.

And the problem with out-of-air drills/training, whether vertical, horizontal, diagonal, or whatever, is that they lack one key element of the real thing (as was sort of alluded to in a previous post). Most of the time when people do OOA drills, they may be holding on to their students, they signal "GO," the student takes a "last" breath, and . . . they're off!!! But in real life, you don't realize you're out of air on your last INHALE, you realize you're out on your last EXHALE. So, no matter how you conduct these drills, if you want to put a taste of reality into them, have the students take off after an exhale, not an inhale (also lessens the chance of embolism).

 

[boulderjohn]

Or . . . it teaches them how far they can go (frequently the length of a pool or 75 feet) exhaling on one breath without running the risk of them embolizing while doing it. And then you add in an explanation that, should they have to do this for real, gas expansion in their lungs while ascending will make it seem "easier" and even extend the range over which they can do this, thereby giving them some back-of-the-brain confidence that, should they ever have to do it for real, might kick in and save their life.

But what do I know? I AM a certified instructor and have been teaching for 40 years.

I, too, am a certified instructor, and my feeling is just the opposite after having taught this countless times. The difference between a horizontal CESA and a vertical CESA is night and day.

Take a look at the video below, a 1958 US Navy video showing training for buoyant ascents for submarine escapes. (The difference between a buoyant ascent and a CESA is essentially the speed of the ascent; PADI teaches that divers should use a buoyant ascent instead of a CESA if they are concerned about reaching the surface with a CESA, with some recommending 30 feet as a rough dividing line.) Note that the trainees are taught to exhale fully before they begin the ascent. Note the amount of air pouring out of their lungs as they prepare to ascend. They then continue to exhale throughout the ascent because when you exhale "fully," there is actually still plenty of air in the lungs, and it needs to be exhaled. These ascents have been done like this (exhale fully first, then continue to exhale) from 300 feet.

The horizontal CESA is not remotely close to that. Students aren't going to make it without full lungs and a very slow exhale. Rather than give people confidence that they can make it, it gives them a fear that they can't. You can see that by looking at any of the countless threads on this topic, in which you will see nearly 100% of the people worrying about being able to ascend while exhaling from depths like 30 feet. You frequently see posts worrying about what happens if they are suddenly out of air without the full lungs they will need to cover that distance. See how many (if any) posts in those threads assure people they can indeed do it with ease, as this video clearly shows.

I have talked with 3 different people who have done actual emergency ascents from depths greater than 75 feet. They all told me that once they started to exhale, the air poured out and seemed to be unstoppable, all the way to the surface.

 

[Ken Kurtis]

Note that the trainees are taught to exhale fully before they begin the ascent.

Blow and go. This is where that phrase came from.
(And please don't anyone post "I've never heard that before." You'll make a bunch of us feel really old.)

Rather than give people confidence that they can make it, it gives them a fear that they can't.

It's all in how your frame and present it IMHO. Frame it positively, your students will perceive it that way. Frame it negatively and you'll get the reaction you're talking about. IMNSHO, the way people react to this says a lot more about how they've been taught rather than their own independently-arrived-at conclusions. As the song from South Pacific says, you've got to be taught.
(And no questions on "What is South Pacific" for the same reason as above.)

 

[Ken Kurtis]

As the song from South Pacific says, you've got to be taught.

Not to beat this to death, but it's sort of like buddy-breathing. I think it's a terrific skill for a variety of reasons. When I was teaching regularly, I'd teach it first night in the pool and by the end of the sessions would have them doing mobile buddy-breathing (BB on the move, simulating an ascent). However, others have been told it's DANGEROUS. And I want to say there are training agencies that prohibit it being taught. My perspective is different. Again, you've got t0 be taught.

 

[Celt]

Not to beat this to death, but it's sort of like buddy-breathing. I think it's a terrific skill for a variety of reasons.

Unfortunately a panicked diver may not give up the donated reg without a struggle.

 

[boulderjohn]

Not to beat this to death, but it's sort of like buddy-breathing. I think it's a terrific skill for a variety of reasons. When I was teaching regularly, I'd teach it first night in the pool and by the end of the sessions would have them doing mobile buddy-breathing (BB on the move, simulating an ascent). However, others have been told it's DANGEROUS. And I want to say there are training agencies that prohibit it being taught. My perspective is different. Again, you've got t0 be taught.

IIIRC, Scuba Pioneer, NAUI Director, and Berkeley professor Dr. Glen Egstrom, who sadly passed away last year, did a study of buddy breathing. He determined that for a specific buddy team to be confident of doing it well in a real life situation, they would need to have completed 17 successful performances in training sessions. They would thus be confident of performing the skill as a team. He also said that team would need to keep practicing it, because the skill is perishable.

One of the people who pushed hard to end buddy breathing as part of instruction a couple decades ago was Dr. Alex Brylske, then the editor of Dive Training magazine and more recently the author of The Complete Diver: The History, Science and Practice of Scuba Diving. I could probably get a comment on this from him if people are all that interested.

I have only heard of one attempt at buddy breathing in a real OOA situation in the last couple decades, almost certainly because almost everyone in the diving world these days uses an alternate air source. In that one situation, a woman was given a rental regulator set with no alternate air source. As luck would have it, another diver went OOA while hunting for lobsters, and she tried to save him by buddy breathing with him. They both drowned. (It was well-covered in a ScubaBoard thread.)

This thread reminds me of an old ScubaBoard regular who frequently repeated two key ideas: 1) There should be no teaching of CESA at all. Zilch. Nada. 2) Buddy breathing is an important skill that should still be part of instruction. In two different threads in which he espoused these ideas, I asked him what he, as an instructor, advised his students to do in the case they found themselves out of air without another diver with an alternate air source. Since he did not believe they should even be told that CESA was an alternative, did he tell them they should instead swim around desperately looking for a diver with no alternate air source so they could buddy breathe? He didn't answer either time, so I never learned what he did tell his students.

Personally, if for some impossible-to-fathom reason I was approached by a panicked OOA diver while I only had one regulator, when I handed that regulator over I would not expect to get it back. I would immediately beginning getting out of my BCD in preparation for a CESA--assuming the panicked diver is not clawing at me and my gear at the same time.

 

[Celt]

when I handed that regulator over I would not expect to get it back.

You won't get it back, the OOA diver who has just suffered the terror of losing there life support will clamp on to the donated reg.

 

[DandyDon]

Unfortunately a panicked diver may not give up the donated reg without a struggle.

In that one situation, a woman was given a rental regulator set with no alternate air source. As luck would have it, another diver went OOA while hunting for lobsters, and she tried to save him by buddy breathing with him. They both drowned.

You won't get it back, the OOA diver who has just suffered the terror of losing there life support will clamp on to the donated reg.

It's a hassle flying with a pony and two regs, etc. but worth it. The second stage in my mouth is a butterfly mouthpiece that didn't catch on but I like it. I used to tell others on the boat that I had two alternate second stages, both would be on, and they could grab either one if needed, but not to grab the one in my mouth as they'd hate trying to insert the butterfly at the time. I don't think my audience paid much attention so I quit. When I think someone might like one, I offer it and squirt some bubbles.

 

[John the Pom]

I, too, am a certified instructor, and my feeling is just the opposite after having taught this countless times. The difference between a horizontal CESA and a vertical CESA is night and day.

Take a look at the video below, a 1958 US Navy video showing training for buoyant ascents for submarine escapes. (The difference between a buoyant ascent and a CESA is essentially the speed of the ascent; PADI teaches that divers should use a buoyant ascent instead of a CESA if they are concerned about reaching the surface with a CESA, with some recommending 30 feet as a rough dividing line.) Note that the trainees are taught to exhale fully before they begin the ascent. ...

And there's an instructor to give you a friendly punch in the guts to remind you ...