Recreational Pony Bottles, completely unnecessary? Why or why not?

[CT-Rich]

Modern submarine ascents usually involve specialized suits, but they were previously done without them. They are actually what most dive agencies would call a buoyant ascent rather than a CESA, but the difference is minor. The difference between a CESA and a buoyant ascent is primarily speed. In a CESA, the diver ascends at a controlled rate of speed (that's the C in CESA), not much more than would be done normally. In a buoyant ascent, the diver inflates and/or drops weights in order to make a more rapid ascent. Buoyant ascents are recommended for deeper depths. You can turn a CESA into a buoyant ascent at any point in the ascent.

Here is a modern video showing two ascents in a naval training tower. The second uses a specialized suit. The first uses a simple flotation device. Note the amount of air being released through the mouth.

This a more vintage video (1958) from the days when this method of submarine escape was first used by the US Navy. I like this video better because the trainees are using almost no gear, and the video shows every step, starting with the initial HUGE exhalation.

The things to notice are how much air is expelled before the ascent begins, and how much air is still available for exhalation after that.

This contrasts mightily with horizontal CESA training, in which there is little to no air expansion, and the ability of the student to complete the exercise depends upon the ability to start with full lungs and continue with only the teensiest amount of exhalation--much like holding one's breath. This exercise gives students a completely incorrect concept of what a real emergency ascent, whether CESA or buoyant ascent, is really like. Most importantly, it gives them the mistaken notion that they can only do it from the shallowest of depths.

In contrast, the 1958 film says that the British navy had done these ascents from more than 300 feet. I have only met a few people who have done true CESAs from depths greater than 75 feet, and each told me that once they started to exhale, there was no stopping it until they reached the surface.

The second 1958 movie goes to show just how dangerous a CESA is. Although they were talking about buoyant ascents, you can see just how seriously they take them. I heard that agencies discontinued practicing them vertically because a few students died in training. I think that really speaks to the attraction of having a pony as a redundant air supply. Much better to be breathing off a reg than trying trying to to master a new skill in an emergenc.

 

[boulderjohn]

Reemphasizing that the C in CESA stands for Controlled...meaning no more than 60 ft/min ascent speed. If one is buoyant, and getting more buoyant as you go up, the speed can easily exceed that, by a LOT, so dropping weights in order to ascend is a last resort.
In fact, historically, PADI OW training gave five ways to ascend: Normally, with an Alternate Air source, CESA, Buddy-breathing (one regulator, shared), and Buoyant. In 1994 PADI stopped teaching buddy-breathing except as an optional skill, and in 2009 dropped it from the curriculum. So now there are just four way to get to the surface, and Buoyant is last choice exactly because it is NOT Controlled. Both the NOAA and US Navy Dive Manuals contain warnings about buoyant emergency ascents, suggesting they are a "last resort."

I recalled that the official PADI wording on this was a tad confusing. Here is what the 2013 OW manual says about the CESA:

This is the best choice if you were completely out of air, no deeper than 6 to 9 metres/20 to 30 feet....(page 161; emphasis added)​

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The buoyant ascent says to use it when you are "so deep that you doubt you can reach the surface any other way."

Well, so what if you are deeper than 30 feet but still think you can do it with a CESA?

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[BoltSnap]

heard that agencies discontinued practicing them vertically because a few students died in training.

I only know of one agency or two, SSI I think, that doesn't require a vertical (to the surface) CESA. At least, with NAUI, we are still required to do it (horizontal and vertical). I also haven't heard much about students dying during/after CESA while in training.

 

[tursiops]

I recalled that the official PADI wording on this was a tad confusing. Here is what the 2013 OW manual says about the CESA:

This is the best choice if you were completely out of air, no deeper than 6 to 9 metres/20 to 30 feet....(page 161; emphasis added)​

​

The buoyant ascent says to use it when you are "so deep that you doubt you can reach the surface any other way."

Well, so what if you are deeper than 30 feet but still think you can do it with a CESA?

​

Hey, if freedom means you don't need a vaccine, you are certainly welcome to CESA from deeper than 30 ft.

 

[boulderjohn]

I heard that agencies discontinued practicing them vertically because a few students died in training.

You are probably talking about several decades ago, when UHMS study found that CESA was the part of training most likely to lead to a fatality. As a result of that study, a number of changes were made to the CESA and especially its training. The biggest problem was the old requirement that the student take the regulator out of the mouth during the ascent, supposedly proving that they were not inhaling. This led to drownings when they did inhale. Current instructions emphasize retaining the regulator in the mouth.

CESA is the only part of the training that has required procedures as carefully laid out as they are.

 

[wetb4igetinthewater]

With heavy exposure protection a controlled ascent can quickly become an uncontrolled ascent. A CESA should be the last resort.

Don't forget the problem if the diver is overweighted and had to add additional gas to their drysuit/bcd to achieve neutral buoyancy. If they are not able to dump that additional expanding gas fast enough, their speed to the surface increases.

 

[Bob DBF]

In contrast, the 1958 film says that the British navy had done these ascents from more than 300 feet. I have only met a few people who have done true CESAs from depths greater than 75 feet, and each told me that once they started to exhale, there was no stopping it until they reached the surface.

Newer test have extended the range:

Submarine Escape from 600 ft Using Rapid Compression and Buoyant Ascent

A relatively new technique of submarine escape has been developed by the Royal Navy. With this technique, in July, 1970, a team of submariners from EMS Dolphin made a series of individual escapes from HM Submarine Osiris at a depth of 600 ft. This system, SET, is now the primary method of escape...

onepetro.org

The hardest part of a CESA is keeping under 60 fpm, once the air expansion fills your lungs its easier.

The biggest problem was the old requirement that the student take the regulator out of the mouth during the ascent, supposedly proving that they were not inhaling. This led to drownings when they did inhale. Current instructions emphasize retaining the regulator in the mouth.

I was never taught or required to remove the reg from my mouth, which is also⁰ convenient if you want to grab that extra breath an empty tank can give you on the way up..

 

[Jcp2]

Wondering about where this extra air from the tank comes from with ascent? If the pressure left in the tank is below the intermediate pressure of the first stage so that no gas can pass through the stage, is there a change in the working intermediate pressure in a balanced first stage with a decrease in depth?

 

[grf88]

Wondering about where this extra air from the tank comes from with ascent? If the pressure left in the tank is below the intermediate pressure of the first stage so that no gas can pass through the stage, is there a change in the working intermediate pressure in a balanced first stage with a decrease in depth?

The first stage will only reach intermediate plus ambient at depth rather than intermediate. As ambient decreases some air will be released. This is assuming the second stage is functioning.

 

[boulderjohn]

This is assuming the second stage is functioning.

...and still in the mouth.