Frequency of advanced divers practicing CESAs ? [Poll]

[johndiver999]

I thought a would relate a story from this weekend. It will have some bearing on this issue.

I was doing a technical dive in which I did something unusual. I had my doubles and a stage bottle for bottom gas, but I breathed down the doubles pretty far before going to the stage (just before ascent) because I wanted to get the doubles down in volume because of future plans. We finished the dive, and I unclipped the stage and deco bottles before something happened that made me want to go back down to about 20 feet for a while. I figured I still had enough left in the doubles to take care of things. Eventually I noticed that it got a little bit harder to breathe, and I knew that meant I was getting pretty low on air. After about 10 breaths, each a little more "draggy" than the one before, I signalled my intent to surface and made a leisurely ascent. I was never out of air.

While that was happening, I thought of the people who insist that OOA incidents always come instantly and without warning, so you might not have a full breath for your ascent.

We've seen many posts on this forum which directly refute your claims. We've been told over and over, with a well tuned and balanced regulator, that when you first detect any resistance to breathing, you MAY get one more breath and that will be it, the regulator will deliver NO more usable air unless you begin to ascend (where decreasing ambient pressure allows more air to exit the tank).

I have always been amazed by these comments and almost universal acceptance of them by the forum participants. A corollary to that idea is: that once the tank pressure is down to the normal intermediate pressure of the regulator, then the regulator can no longer deliver a meaningful amount of air.

These comments (by others) are in direct contradiction to my own experience, as I have done what you describe many times.

Of course you can sip air from a tank with very low pressure, anyone who doubts it can purge a tank down to near zero and try to use the regulator (while sitting under a tree). It takes quite a while to completely drain the tank once it gets a little hard to inhale - especially if you "test" the tank/regulator with a really fast and deep inhalation when you suspect you are getting to the bottom of the barrel. Another trick if you think the tank is very low, is to press the inflator and inhale really hard. You will feel the sluggishness in air delivery a lot earlier under this scenario.

If you had checked a mechanical spg during the re-descent, chances are it would have shown zero psi or something very close to it. When a tank gets really low, a diver should understand that it doesn't matter what the spg says, if the regulator is getting sluggish, you are down toward E.

If you are actively swimming and moving and inhaling at a good rate, you will detect the sluggishness when a tank gets low. However, if the diver is super calm, say laying on the bottom doing macro photography and deliberately sipping their air very slowly, then they CAN really drain a tank quite low without being able to feel it.

 

[TrimixToo]

My experience in breathing stages (not back gas, not deco gas) very low is that I notice several normal breaths before the tank is empty that resistance is increasing. I have measured the tank pressure afterward to find it 10-20 PSI higher than the IP+ambient where the tank ran low. Mares Abyss regs at 300' or so, if it matters, and this is while finning just short of moderately. I have never breathed my back or deco gas down low enough to see if my variety of deco regs do the same, though. This is my direct, personal experience, and I would assume that what @boulderjohn posted was his direct observation as well. That does not mean that different equipment than he and I happen to use would yield the same results.

 

[TMHeimer]

I am certainly no authority on breathing tanks down so low. Agree that different equipment would probably behave differently. If all nearly OOA situations gave some warning with resistance when inhaling, I would surmise there would never be a need for a CESA--just make a normal ascent and with the pressure change you will be able to get to the remaining gas in your tank. So I guess sometimes you just get one or 2 breaths, then nothing--thus the reason CESA is even taught?

 

[Diver-Drex]

Return of the j valve... because looking at your spg is too much to ask for some...

I am certainly no authority on breathing tanks down so low. Agree that different equipment would probably behave differently. If all nearly OOA situations gave some warning with resistance when inhaling, I would surmise there would never be a need for a CESA--just make a normal ascent and with the pressure change you will be able to get to the remaining gas in your tank. So I guess sometimes you just get one or 2 breaths, then nothing--thus the reason CESA is even taught?

The CESA is taught with the second stage in your mouth. As you ascend you may involuntarily inhale and should get a breath. Much better than the free ascent they used to teach and I had to perform as part of certification.

 

[Clayton122]

Horizontally in the pool. There is no compelling reason to do it otherwise. The risks for a single diver doing it once is amplified for an instructor doing it multiple times.

When we teach CESA in class, we use the horizontal method in the pool.

But in the Quarry where we do the checkout dives, we generally have whichever instructor of us is doing the training that day wrap themselves in a buoy line that is attached to the training platform. The instructor grabs on to the student, and then we tell the student to perform the exercise, trying to pull he instructor to the surface ( which cant be done since were wrapped in the line ).

I have heard of instructors getting bent doing this multiple times a class, so this was the solution my LDS came up with, and have been using since before I joined their DMC program. It seems to work well.

 

[boulderjohn]

When we teach CESA in class, we use the horizontal method in the pool.

But in the Quarry where we do the checkout dives, we generally have whichever instructor of us is doing the training that day wrap themselves in a buoy line that is attached to the training platform. The instructor grabs on to the student, and then we tell the student to perform the exercise, trying to pull he instructor to the surface ( which cant be done since were wrapped in the line ).

I have heard of instructors getting bent doing this multiple times a class, so this was the solution my LDS came up with, and have been using since before I joined their DMC program. It seems to work well.

In which case, the student does not have the experience of air leaving the lungs through expansion.

 

[Clayton122]

In which case, the student does not have the experience of air leaving the lungs through expansion.

Agreed, but we deemed it to be the safest way to teach the skill. We obviously require them to blow air when doing it in a manner in which we can hear them. They may not feel the same sensations, but the skill they learn is identical. NAUI had no issues with this method either. We are simply trying to make the exercise as safe as we can for everyone involved. That includes the instructor.

 

[boulderjohn]

They may not feel the same sensations, but the skill they learn is identical.

No, it isn't.

Read through this thread.
Today's 136ft CESA trial

 

[Clayton122]

No, it isn't.

Read through this thread.
Today's 136ft CESA trial

I guess we will have to agree to disagree. NAUI is comfortable with it, so that works for me. I believe this is the safest possible method to teach and practice this skill without risking someones health.

 

[northernone]

I guess we will have to agree to disagree. NAUI is comfortable with it, so that works for me. I believe this is the safest possible method to teach and practice this skill without risking someones health.

I find the risk of a shallow water blackout with a prolonged exhale while breath holding in the pools depths during a moderate workload drill will introduce risks I do not want to deal with.

Bringing up the resulting unconscious diver and resussitating them during an OW class has risks that the traditional CESA drill doesn't.

(Regarding the tethered instructor idea: I'm fairly horrified in the resulting lesson learned by a drill method where the student must struggle unsuccessfully to ascend and PREVENTS them from being able to surface while feeling air starved and trapped underwater unable to breath. That's the two last things I want to enforce in a new diver.)

Discussion welcome.