CESA Question

[Superman541]

I became a certified PADI Open Water Diver yesterday. In Puget Sound. In December. Headed for Cozumel next month. Go me!

PADI says the Controlled Emergency Swimming Assent should not be used from depths greater than 30 feet. This raises some questions in my mind. First, just exactly what is someone supposed to do if they run out of air at 100 feet of depth and an alternate air source is not available? I guess the only alternative to dying would be to exceed the safe assent rate and just get to the surface. Am I missing something here?

I also know that running out of air does not just happen by accident. It should never happen.

Here is another curiosity: What do free divers do? We've got a free diving depth record of more than 800 feet. Do free divers hold their breath until they actually return to the surface several minutes later? Are they not risking decompression sickness?

Thank you, in advance, for considering my questions.

 

[tbone1004]

a few things to unpack here.

Free divers hold their breath from top to bottom but they are not breathing compressed gas so they are not susceptible to lung injuries from expansion. If you take a breath from scuba at 100ft and hold it to the surface that gas will become 4x as large when it hits atmospheric pressure which will cause your lungs to explode. A freediver takes a full breath of air at the surface and at 100ft their lungs shrink to 1/4 the size and expand back.
Free diving does expose you to DCS risk, hell whales experience DCS as well but they are down for very short amounts of time so it's not a significant concern.

With regards to PADI's recommendation of 30ft or shallower, that is largely because of the lawyers. If you're at 100ft you get to the surface and deal with whatever happens. Try to never put yourself in that position but if you get stuck then bent is better than dead. Now an AGE if you forget to exhale is basically an excruciatingly painful death so make sure you blow those bubbles the whole way up, but we can unbend someone a lot easier than we can bring them back from the dead.

 

[Skeptic14]

If you're properly buddy diving than you should have an "alternate" air source near by, ie your buddy.

If you're properly solo diving you should have a secondary air source.

Free divers didn't take their breath at depth like when on scuba, so the considerations regarding ascent are different.

It should be considered inexcusable to run out of air; it should be very methodically monitored.

 

[Superman541]

Thank you!

After further consideration, perhaps I have figured out why free divers are not at risk of decompression illness despite spending several minutes in hundreds of feet of depth. You see....the grand total of all nitrogen available for saturation into their blood is limited to only that nitrogen in the single breath they take with them on their journey.

 

[Angelo Farina]

CESA stands for Controlled Emergency Swimming Ascent, and is recommended to be practiced only from shallow depth (10 meters or less).
In case of emergency at greater depth, and no help from your buddy, there are several ascent options:
1) Uncontrolled Emergency Swimming Ascent, which just means swimming up faster than the recommended 10 meters/minute
2) Controlled Emergency Buoyant Ascent, using your BCD or releasing weights
3) Uncontrolled Emergency Buoyant Ascent, also called "corking". The most dangerous one, of course.
These ascent procedures are not really "safe", but, as others already explained, "better bent than drowned".
In my experience as an instructor, any of these three "unsafe" ascent procedures, and particularly the third one, is usually triggered by panic or loss of breathing control (these two accidents are often inter-related), not by a true "out of air" condition, which is objectively quite rare.
Panic instead can be triggered by every minor unexpected event, and loss of breathing control can happen even to experienced divers, as it is an involuntary reflex caused by CO2 retention. A vicious circle which is dfficult to interrupt.

 

[boulderjohn]

They suggest that the depth limit for a CESA is 30 feet. Deeper than that, you are supposed to use a buoyant ascent. The difference is the "C" in CESA--controlled. The buoyant ascent is exactly the same as the CESA, except you drop weights and/or inflate the BCD so that you will be heading to the surface with ever increasing speed rather than using a normal ascent rate as in the CESA. Getting bent is indeed better than drowning.

I personally would choose a CESA from much deeper than 30 feet.

 

[wetb4igetinthewater]

OT: i hope you keep diving in the Puget Sound. Welcome!

 

[boulderjohn]

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.

 

[Angelo Farina]

They suggest that the depth limit for a CESA is 30 feet. Deeper than that, you are supposed to use a buoyant ascent. The difference is the "C" in CESA--controlled. The buoyant ascent is exactly the same as the CESA, except you drop weights and/or inflate the BCD so that you will be heading to the surface with ever increasing speed rather than using a normal ascent rate as in the CESA. Getting bent is indeed better than drowning.

I personally would choose a CESA from much deeper than 30 feet.

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.

 

[Scraps]

Superman541:

Congrats on your certification and double congrats for making the effort to keep thinking about safety even after your class.

You should be able to dive for a lifetime without ever needing to use the CESA. It is indicated only in circumstances in which you screw up TWICE: first by running out of air and second by not staying within reach of your buddy, who is your alternate air source.

Of all the divers in my acquaintance, I am aware of only one who has actually had to do one.

If you do find yourself out of air and closer to the surface than to your buddy, you can take comfort in the fact that thirty feet is not a magic limit to the effectiveness of the CESA technique. It just happens to be the deepest the training agency wants people to practice it.

My friend who needed to perform one started his at 70 feet.

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. He claimed his extra breath around thirty feet and it got him to the surface without having to resort to any of the uncontrolled or buoyant ascent options, which are especially dangerous for divers who have been down long enough to deplete their breathing gas supply.

Best wishes on never needing to verify this for yourself.

*Edited to reflect @boulderjohn’s correction/clarification.