Confident CESA depth?

[Akimbo]

... Want to take bets on whether that is done on a full inhale?

I did several experiments from 60' about 45 years ago to answer that question very question in my mind. I started each free ascent with what I judged to be at the low end of my "normal" respiratory cycle. It was a little worrisome until I got to around 40', but probably more because I was on the negative side buoyancy-wise. Remember, no BCs in those days so dives began on the heavy side with full tanks. Thankfully wetsuit compression was much less then due to the stiffer Rubatex material. Even at that age I wasn't stupid enough to do my free ascent exercises at the end of my dive.

Lots of variables... that's why divers need to experience it themselves. There's a lot more to discover than proof that the gas laws work.

 

[dmaziuk]

Ahhh but the OP's estimate of his safe CESA depth was based on an underwater horizontal swim. Want to take bets on whether that is done on a full inhale?

True, but a) I said "comfortably", b) I also do one after the workout, with some amount of O2 debt, which wouldn't be the case after my typical dive, and c) translate my full inhale at sea level to "empty lungs" at 5 atm.

I don't for a second doubt that after a leisurely dive to my cert-approved depth I'll have enough oxygen for minutes. I strongly doubt I can come up slowly enough, and that I can vent enough CO2 to keep the urge to breathe down -- both of which are going to get worse as I get closer to the surface, of course, Murphy at his finest.

 

[Akimbo]

I strongly doubt I can come up slowly enough...

Slowly enough for what? Probably true for 30'/minute and a safety stop. How about 60'/minute and no safety stop that was the standard most of my life (and I have never had DCS symptoms)? Or better yet, 120'/minute like a typical freediver and making it to the surface "possibly" bent but avoiding drowning? Keep in mind we are largely discussing the option that sucks the least when everything goes wrong and is conspiring to kill you.

 

[dmaziuk]

Slowly enough for what? Probably true for 30'/minute and a safety stop. How about 60'/minute and no safety stop that was the standard most of my life (and I have never had DCS symptoms)? Or better yet, 120'/minute like a typical freediver and making it to the surface "possibly" bent but avoiding drowning? Keep in mind we are largely discussing the option that sucks the least when everything goes wrong and is conspiring to kill you.

I am nitpicking: the problem was originally stated as

... you can arrive there in good health. Also not rocketing fully positively buoyant or arriving unconscious.

I always thought of CESA as "better bent than drowned", too, and technically I'll probably not arrive with clinical DCS symptoms: they'll take a few minutes do develop, so does that count as "good health"?

My leisurely horizontal swims are probably around 20-25 seconds for 25 yard length, that's close to 240'/minute. Even with BP& empty tropical wing I expect gear drag to cut that in half, I'd say 120'/minute if I manage to keep my cool and slow TH down all the time.

 

[northernone]

I am nitpicking: the problem was originally stated as



I always thought of CESA as "better bent than drowned", too, and technically I'll probably not arrive with clinical DCS symptoms: they'll take a few minutes do develop, so does that count as "good health"?

My leisurely horizontal swims are probably around 20-25 seconds for 25 yard length, that's close to 240'/minute. Even with BP& empty tropical wing I expect gear drag to cut that in half, I'd say 120'/minute if I manage to keep my cool and slow TH down all the time.

Been thinking on your question. To me the key word is "controlled" emergency swimming ascent. Being able to go up at whatever chosen ascent rate you feel will likely get you to the surface in good health (unbent). I accept the risk of DCS on every dive regardless of profile. Some dives are riskier than others though.


I'll consider a "better bent than drowned" ascent being done at a high rate of speed and likely positively buoyant (better if arriving unconscious at the surface provided your bcd doesn't float you face down... I have a buddy alive because he floated face up after a blackout) and that done deeper than I can calmly swim up from. The question is posed from the perspective of "no stop" dive profiles. If I'm omitting mandatory decompression stops I'm not expecting to be in good health. What is a safe enough ascent rate is a matter of risk tolerance and medical research. There's some pretty good threads running discussing that.

All in all, keeping calm if multiple failures occur may save my life and having another tool in my "staying alive toolbox" is valuable to me.

Regards,
Cameron

 

[Bob DBF]

Those who think the CSEA is obsolete because it won't happen to me because I plan my dive better, reminds me of the pushback I got back in the day for retrofitting my vehicles with seat belts and using them before they were standard equipment.

The CESA is not, and never was, a remedy for poor gas planning. It it is a last ditch procedure to save one's life from a dangerous environment. It was pointed out to me early that I can't breathe water so I had to learn to swim, which led to snorkeling, then freediving, and finally SCUBA. I still can't breathe water and a CSEA is my last ditch effort to stay alive.



Bob

 

[Dave Bevan]

Those who think the CSEA is obsolete because it won't happen to me because I plan my dive better, reminds me of the pushback I got back in the day for retrofitting my vehicles with seat belts and using them before they were standard equipment.

The CESA is not, and never was, a remedy for poor gas planning. It it is a last ditch procedure to save one's life from a dangerous environment. It was pointed out to me early that I can't breathe water so I had to learn to swim, which led to snorkeling, then freediving, and finally SCUBA. I still can't breathe water and a CSEA is my last ditch effort to stay alive.



Bob

Whilst I agree to a certain extent with what you are saying I hope to complete my entire diving career without ever doing one. I understand the principle and technique as a last ditch attempt but honestly I would put it even behind something like a seatbelt on a car.

I think it really can be avoided. I have to believe that as most of the diving I'm doing these days has a hard or soft ceiling. I think with the right training and team principles it shouldn't ever happen. But then I also understand the real world implications of Insta buddies and of course the human condition.

 

[CWK]

I dive with 2 different alternate air sources. The first is a pony. The second alternative air source has more air the deeper I dive .. it is my BCD. I have actually tried a "CESA" or OOA swimming ascent whilst breathing from my BCD.

 

[Dave Bevan]

CWK I wouldn't keep rebreathing your BCD you'll end up with a chest infection or worse you'll black out and drown. Breathing loops need to be disinfected often with anti bacterial.

 

[dmaziuk]

The question is posed from the perspective of "no stop" dive profiles. If I'm omitting mandatory decompression stops I'm not expecting to be in good health. What is a safe enough ascent rate is a matter of risk tolerance and medical research. There's some pretty good threads running discussing that.

I think if 60m is the max depth for no-stop dives, anyone capable of the 25m underwater swim required by e.g. AAUS should be OK coming up from half that. Without freediving training I'd expect 40m to be uncomfortable and full 60: very uncomfortable. But very doable. As for DCS risk, at the end of a dive I would worry about fast tissues when swimming up at 30-40m/minute, and I doubt I can realistically swim up much slower than that. If I just splashed and found my gear is fubar, meh. Anything under 4 minutes (or is it 2?) doesn't even count, right?