Today's 136ft CESA trial

[yle]

2. Getting negative as the tank floods with water is another risk a catastrophic failure can cause. The buoyancy shift is dramatic and I haven't heard it addressed.

Interesting... the buoyancy change would be about 20 pounds to the negative, give or take a few pounds, depending on the size of the tank. Unless you're wearing 20 pound of ditchable weight that could be dropped to compensate, might have to ditch the tank itself.

Of course the time needed for the tank to fully flood would be much much greater than the few minutes it would take you to reach the surface.

 

[BRT]

Flooded tank, now what?

Just what rjack said. It takes a small amount of water to equalize.

 

[rjack321]

so 250mL of air was displaced... if you go down the air will be compressed and some water is going to go in sure.
Pretty much zero deceased divers were recovered with a water filled cylinder, even the ones who are recovered years after their death.

 

[EireDiver606]

5 months later did it again.

200ft up to 70ft. Modified the practice this time.

Started off with an empty bcd and fairly significantly negative (12lbs negative if I needed to guess). Narced more noticeably in the 180-140 range after the co2 build up from the effort of finning up got me.


Doing it for real I would have ditched 4lbs at least.

Once I hit 140ft it was comfortable again after passing the dark narc depth range. Being in brighter water feels better too.

Maintained a comfortable ascent rate (new slow suggested ascent).

Well. That's that.
Cameron

I’ve never tried it myself but is 5kg negative not extremely hard to swim up against?

 

[northernone]

so 250mL of air was displaced... if you go down the air will be compressed and some water is going to go in sure.
Pretty much zero deceased divers were recovered with a water filled cylinder, even the ones who are recovered years after their death.

Fair enough.

I do agree if the inside of your only air cylinder is below ambient pressure and sucking in water to equalize you are having a bad day on many levels. I too can't think of a scenario in open water where it would be likely... if your plunging to the depths out of air already the fact your tank is slowly taking on water is probably the least if your worries.

I’ve never tried it myself but is 5kg negative not extremely hard to swim up against?

For me that's is a heavy workload at that depth.

Can be tested in a pool for curiosity sake:
How much weight can YOU swim up?

 

[John C. Ratliff]

I would like to add one little bit here. Some have said that Shallow Water Blackout is not a problem for these trial CESA. Normally, I would agree, but my assumption is that the diver is breathing air at depth. However, if someone were to try this type of emergency ascent from really deep water, and was breathing tri-mix with a fairly low percentage of oxygen, then this emergency ascent could cause the diver to experience Shallow Water Blackout, especially if this were an actual emergency and the ascent were continued to the surface.

SeaRat

 

[northernone]

I would like to add one little bit here. Some have said that Shallow Water Blackout is not a problem for these trial CESA. Normally, I would agree, but my assumption is that the diver is breathing air at depth. However, if someone were to try this type of emergency ascent from really deep water, and was breathing tri-mix with a fairly low percentage of oxygen, then this emergency ascent could cause the diver to experience Shallow Water Blackout, especially if this were an actual emergency and the ascent were continued to the surface.

SeaRat

An excellent warning. Thank you for highlighting this safety issue.

I would not do this trial on a hypoxic gas nor take it right to the surface. My "real" deep air CESA trial days are behind me (I use to practice from significant depth to surface). Now from trimix depth a CESA is not in my planning so I do not feel the need to practice it deeper. The principal remains the same.

Regards,
Cameron

 

[boulderjohn]

That said, I make my airways an open loop, head up, with an open throat and mouth, the gas flows out "automatically" as it expands. I'm neither not blowing out to increase the airflow nor locking my throat shut trapping the gas. I hold my body (explanation unclear, I apologize) at a fixed level of relaxation and let the expanding air "overflow" as it wants to as I ascend.

I have long argued that teaching the horizontal CESA in the pool as we do is detrimental because of this. With little to no expanding air (depending upon the amount of ascent, if any), the students must actively exhale, and if they it too quickly, they run out of air along the way. They therefore must use a technique to limit their exhaling, thus practicing a technique they do not need in a real CESA. Having seen how difficult it is to travel that distance with that limited exhalation, they become convinced that they cannot make it if it were to become necessary in real life. That means they are more likely to panic and hold their breath in a real OOA situation.

Furthermore, they fail the horizontal exercise if they inhale near the end of the swim. We are therefore teaching them that they will not have any air along the way, even though the change in pressure in a real event will allow them to inhale as they ascend. If anything, we should reward them for taking a sip of that air at the end, not punish them.

 

[dmaziuk]

I have long argued that teaching the horizontal CESA in the pool as we do is detrimental because of this. ...

What I do is for the 1st length of my front crawl pull drill I keep my airway open as Cameron describes. It's pretty much a proper head position for front crawl anyway, and you need to create a little back-pressure to keep water from getting up your nose. So it works out to how one would do it horizontal in the pool.

Except that I'm doing front crawl pull at about 1m/s.

 

[boulderjohn]

Except that I'm doing front crawl pull at about 1m/s.

So at less than 10 seconds to complete the 30 feet. We are supposed to fail students who go that fast.