CESA Training

[Edward3c]

Perhaps. Especially since the diver (in this case) had a redundant supply available. Is it an emergency situation when a diver is at 90 feet and it begins to get hard to inhale from the tank and there is no redundancy available? I don't know.

You've indicated that one organization has not collected even one incident of a CESA in 10 years, yet most of us know of divers who have been irresponsible and run their tank down way too low. So perhaps there would be more CESA's recorded, if the definition were defined more clearly or broadly?

Is there an agreed upon definition of CESA's?

The definition is as taught. What you described isn’t, but would be included in incident reports, if it was recorded.

 

[boulderjohn]

Perhaps. Especially since the diver (in this case) had a redundant supply available. Is it an emergency situation when a diver is at 90 feet and it begins to get hard to inhale from the tank and there is no redundancy available? I don't know.

PADI teaches this priority for a low on air/out of air emergency:

1. Normal ascent
2. Share air via alternate source
3. CESA
4. Buoyant ascent

The most misunderstood is the #1 choice--normal ascent. The original thinking on that is that if you realized it was getting harder to breathe because you were low on air, a normal ascent should get you to the surface easily. That idea seems to be lost today.

A couple years ago I went to Rubicon and did a search for documents dealing with the history of teaching emergency ascents. There were many articles in the early 1970s in which people suggested strategies they had tried, and you can see the CESA develop before your eyes. (Most articles came out of Australia, IIRC.) One idea they had then that has carried through to the modern era (unfortunately) was teaching students to recognize a tank that is getting low on air by shutting off the air. I don't know what regulators were like then, but that absolutely does not work today. With the air shut off in shallow water, the diver simply goes from breathing fine to getting nothing in a heartbeat. That is not what happens as the diver's tank gets close to critical pressure and the diver has to pull harder to compensate for the lessenting pressure in the tank.

 

[scubaozy]

PADI teaches this priority for a low on air/out of air emergency:

1. Normal ascent
2. Share air via alternate source
3. CESA
4. Buoyant ascent

The most misunderstood is the #1 choice--normal ascent. The original thinking on that is that if you realized it was getting harder to breathe because you were low on air, a normal ascent should get you to the surface easily. That idea seems to be lost today.

A couple years ago I went to Rubicon and did a search for documents dealing with the history of teaching emergency ascents. There were many articles in the early 1970s in which people suggested strategies they had tried, and you can see the CESA develop before your eyes. (Most articles came out of Australia, IIRC.) One idea they had then that has carried through to the modern era (unfortunately) was teaching students to recognize a tank that is getting low on air by shutting off the air. I don't know what regulators were like then, but that absolutely does not work today. With the air shut off in shallow water, the diver simply goes from breathing fine to getting nothing in a heartbeat. That is not what happens as the diver's tank gets close to critical pressure and the diver has to pull harder to compensate for the lessenting pressure in the tank.

In the years I started teaching,3. CESA was followed by 4. Buddy breathing. This was also an exam question which was very frequently gotten wrong by the students. I was happy when buddy breathing made optional. Never missed it but I can’t say the same for CESA. If it was optional I would probably choose to teach it.

 

[scubaozy]

The definition is as taught. What you described isn’t, but would be included in incident reports, if it was recorded.

Do you consider this cesa:
September 2019 19/236
A diver and his buddy, both using air, carried out a boat dive. The diver was using a 12 lt cylinder with 230 bar instead of his usual 15 lt cylinder as the dive was relatively shallow with good conditions and underwater visibility. The pair descended and explored a wreck. The diver checked and let his buddy know he had 120 bar fairly early into the dive. He did not look at his contents gauge for some time but when he checked he had 50 bar so immediately signalled his buddy. He gave a second signal when he was on 30 bar which the buddy mistook as the diver wanting to ascend in no more than 3 min. The buddy led the way back to the shotline and they ascended with the buddy unaware how low the diver's air was. Towards the end of a 3 min safety stop at 4m the diver signalled 'out of air', 'up' and made a controlled ascent. He had felt that as they were just below the surface he did not think it was necessary to take his buddy's alternate source. He surfaced with a dive duration of 44 min to a maximum depth of 17m. His buddy surfaced almost straight after and, with a fully inflated his wing BCD which the diver held onto, he orally inflated the diver's BCD.

 

[Edward3c]

Do you consider this cesa:
September 2019 19/236
A diver and his buddy, both using air, carried out a boat dive. The diver was using a 12 lt cylinder with 230 bar instead of his usual 15 lt cylinder as the dive was relatively shallow with good conditions and underwater visibility. The pair descended and explored a wreck. The diver checked and let his buddy know he had 120 bar fairly early into the dive. He did not look at his contents gauge for some time but when he checked he had 50 bar so immediately signalled his buddy. He gave a second signal when he was on 30 bar which the buddy mistook as the diver wanting to ascend in no more than 3 min. The buddy led the way back to the shotline and they ascended with the buddy unaware how low the diver's air was. Towards the end of a 3 min safety stop at 4m the diver signalled 'out of air', 'up' and made a controlled ascent. He had felt that as they were just below the surface he did not think it was necessary to take his buddy's alternate source. He surfaced with a dive duration of 44 min to a maximum depth of 17m. His buddy surfaced almost straight after and, with a fully inflated his wing BCD which the diver held onto, he orally inflated the diver's BCD.

The bit from 4m to the surface, from the description, sounds like it would qualify.

 

[Subcooled]

Why?

Because... I have done it and...

when your life actually depends on a successfull emergecy ascent,
- controlled or not,
- buoyant or swimming,
you really, really want to have done it at least once before.

The resulting confidence and clarity of mind might save your life.

Freediving 25m horizontally is easy and freediving 50m horizontally is doable for anyone reasonably fit and relaxed with a little practice (well I did it many many times without being an athlete).

The limit here is the amount of oxygen in the blood (and also mental state: how well do you tolerate CO2?). Oxygen dictates how far you can dive without loosing consciousness (for me it was 65m untill passing out) and CO2 dictates how **** you will feel during the dive and when you will panic. Feeling bad is a mental hindrance only, though. OK, too little O2 or too much CO2 can both kill, but most likely it is the oxygen percentage that is relevant. 25m horizontally is easy, 25m vertically is even easier (given a SCUBA set).

When one dives at depth and breathes high pressure oxygen then there is some extra O2 in the blood. That would be enough to maintain your consciousness from far greater depths that 25m (if normoxic air takes you 25-65m!). Breath hold also does not feel that bad, because as you ascend and the air in your lungs expand, you can/must exhale and get rid of some CO2!

And hey, it's not a CESA, it is an EA.

I have done an emergency ascent only twice, once form 10mts and once from 20mts, but two things are certain:
1) emergency ascents are not controlled vs. uncontrolled - they just are; you want to get to the surface, no matter how. Style is not a factor here.
2) swimming or buoyant? Who the f cares? You want to reach air.

 

[Subcooled]

Would it be considered safe to practise CESA training from 10 then 20 and eventually 30 meters?

Absolutely!

I mean... 25m is no distance for a freediver... it only gets more challenging after 50m...

You have drag inducing gear but you also have a BCD to make your ascent buoyant (which is a great thing on dives that do not demand mandatory decompression stops).

I have done a real emergency ascent from 20m with an empty tank and it was easy.
I am absolutely sure that I could have done it from 30m or even from 40m,
because I had a small 7 litre tank and I had air to spare.

As ambient pressure drops to 1/2 (20m=3bar to 5m=1,5bar) there were suddenly several breaths of air available.

Keep the reg in your mouth.

The idea would be to do it with a full tank, valve opened and surrounded by an Instructor and a DM.

Or one experienced buddy. I am sure your 10m drill and 20m drill both are very very easy. If you ever do it from 30m then it gets a lot more challenging mentally, and from 40m it would be really serous (DCI risk and all).

I haven't asked my Instructor yet.

Let me guess: In the U.S. everybody says no.

While exhaling and ascending, if I am out of breath, I will still have the possibility to inhale through my regulator.

OK, so you have never ever ran out of air for real? Let me tell you secret. It is not a 100->0 event. You will notice an increasing resistance when you try to inhale. When you realise that... of ****... I'm out of air... you will have three to five breaths left. It is a lot, I tell you. Just swim to the surface, OK?
I know that in a real OOA situation, some gas is supposed to be available as one ascends but I am not insane enough to test that.[/QUOTE]

 

[Subcooled]

And, oh, I need to warn you:
These things that I am writing about,
they are easy,
IF you are an experienced diver,
AND you can keep your mind calm.

 

[dmaziuk]

Ascent speed is not that important unless the dive has been excessively deep (long deco obligation, trimix, and stuff).

Depends on your definition of important. 1) On no-stop dives your DC may be factoring ascent time into its NDL calculation so if you're riding the limit, a fast emergency ascent could push you over the M-value. Which of course doesn't mean you'll have a problem, it just means your chances of having the problem increased slightly. 2) Fast ascent can cause excessive bubbling -- you'd also need to have enough dissolved gas to make bubbles, i.e. you'd be at more risk after a longer deeper dive.

Whether the increase in risk is important or not is in the eye of the beholder.

 

[Raphus]

When one dives at depth and breathes high pressure oxygen then there is some extra O2 in the blood.

Correct me please, if i am wrong.. But
At high pressure the ppO2 increases.
So for example.if you got 10% oxygen, which is not enough at the surface.
You got a ppo2 of 0.2 at 10m.

But the amoung of oxygen in your blood should be the same, if ppo2 is over/arround 0.2
As far as i know, that's the maximum amount of o2 that can be used by our bodys.

More ppo2 will not cause more o2 to disolve Into the blood.