CESA over Shared Air Ascent: Which is Best

[raymond phule]

The pressure differential at 25' (1.76 ATA) is 176% that of surface pressure. While NDLs are very long, you will bubble on direct ascent after an exposure of less than half the NDL. While it is highly unlikely this bubbling would result in full blown DCS, it would be highly likely to result in sub clinical DCS symptoms such as fatigue.

Just curious, do you have a reference for this bubbling and sub clinical DCS from 25'?

The fastest dsat (padi) m-value that could be a problem is the 200 min compartment. It saturates after 1200 min = 20 hours so the NDL time would be something like 20 hours. Ok, if you dive 10 hours at 25' feet make your safety stop.

The pressure differential at 15' feet is by the way 145% are you sure this one is safe?

so I have to ask why you would choose an emergency ascent strategy that would result in sub clinical DCS symptoms and laugh at divers who choose a strategy that does not present that issue.

I have to ask, are you kidding? Safety stop at 15' feet completely safe. Diving at 25' without safety stop is supposed definitely result in sub clinical dcs?

edit: wrote a couple of zeros to much...

 

[oly5050user]

the original question was if it is safer to do a cesa from a 25' dive or a share air ascent....now you throw in safety stops(which are not required on a recreational 25' dive)...still safer to do a cesa..By share air you mean an alternate air source and the buddy is right there then that can be preferred,but no need for a safety stop. Buddy breath,forget about it ,most recreational divers who have not praticed it with a constant buddy would not be able to stay cool enough to do it.Why add something to an already stressed out diver when it is not needed? If I personally had a problem in that instance I would do a cesa,its no big deal when done correctly.
As to the >1ata comment i did not catch the ">" sorry...

 

[Al Mialkovsky]

The pressure differential at 15' feet is by the way 145% are you sure this one is safe?

You don't bolt to the surface after a safety stop either, as I said my computer will only allow an ascent rate of 23 fpm from 15 feet. It's a very slow ascent even then, one performed better sharing air and possible while sharing air, impossible while doing a cesa.

Oly you've ignored my last post directed towards you, well done.

 

[raymond phule]

My post was about the no safety stop sub-clinical dcs, safety stop no sub-clinical dcs claim

It's a very slow ascent even then, one performed better sharing air and possible while sharing air, impossible while doing a cesa.

I dont know, I dont have any problem to freedive down to 25' and make a slow ascent from there. I definitely dont need to bolt to the surface atleast and I am not good at freediving.

This thread seems to be alot about using fuzzy uncertain rules as 100% sure rules and you are going to die if you dont follow them.

Why stop at a 3 min safety stop? Isn't a 10 min safety stop going to be better?

Maybe 5 min at 5 m, 10 min at 4 m, 15 min at 3 m, 20 min at 2 m, 30 min at 1 m and an hour at 0.5 m plus a 0.1 m/min to the surface. I believe it is safer compared to the obsolute old school 3 min at 15' rule.

 

[Al Mialkovsky]

Ray we are talking about a shared air vs a cesa, something I doubt you'll do while freediving

What I said earlier is when I do a shallow dive it's normally a shore dive, if I follow the bottom back in I'll end up with a safety stop regardless since I'm spending a few minutes in the safety stop zone just swimming back. But I always do a safety stop as I'm no longer young and no longer an athlete. I've seen people get bent following dive tables that said they didn't need a safety stop. So why not enjoy the dive for a few extra minutes and get in a safety stop?

Is a safety stop safer than no safety stop? For those of us who are professionals yet laugh at those of us who will be 'extra' safe is irresponsible at best.

 

[Darnold9999]

Are you referring to the belief that it is better to do a safety stop than to not do a safety stop?

Where would you draw the line, in terms of depth? 30'? 60'? Does the formation of 'silent bubbles' have any impact on your decision or are the NDLs the only factor you consider?

The pressure differential at 25' (1.76 ATA) is 176% that of surface pressure. While NDLs are very long, you will bubble on direct ascent after an exposure of less than half the NDL. While it is highly unlikely this bubbling would result in full blown DCS, it would be highly likely to result in sub clinical DCS symptoms such as fatigue.

As an instructor, I'm sure you know all this, so I have to ask why you would choose an emergency ascent strategy that would result in sub clinical DCS symptoms and laugh at divers who choose a strategy that does not present that issue.

Interesting how you went from "bubble at less than half the NDL" to "would be highly likely to result in sub clinical DCS" to "would result in sub clinical DCS" all in the space of two paragraphs.

You seem really invested in this point of view i.e. CESA is never the best strategy. Me I prefer the stop, think and choose the best strategy based on the situation at hand. The "risks" of DCS and of blowing off a safety stop from a 25' dive are far less than the risks we all accept routinely doing 100' dives with a safety stop. This part of your arguement I am afraid just doesn't hold water.

I just don't get the extreme focus on the safety stop. It is there as an additional safety precaution, and on a 25' dive I don't recall that anyone even recommends it as it adds exactly nothing to your margin of safety against DCS.

You are emphasising all of the possible risks of a CESA and assuming that there are absolutly no risks associated with sharing air. While I accept that there are risks in doing a CESA particularly if you panic and rocket to the surface, there are risks associated with sharing air. Notabley that something goes wrong in the excitement of the moment. From virtually no risk with your regular dive buddy with whom you practice this regularly - to significant risk with an instabuddy you just met. Your mythical "competant buddy" falls somewhere in the middle. At 25' I choose CESA as the lower risk solution with anyone but a regular buddy - feel free to choose something else, but nothing you have said convinces me that an air share is the obvious best choice in the situation described.

 

[24940]

The OP was pretty clear in defining a scenario which was quite conservative....extrememly so, even. The question was quite simple: given the parameters defined, which is the better emergency ascent procedure? Many divers gave reasons why a shared air ascent would be a better option than CESA, but what I saw as justification for CESA just didn't play out against the scenario in the OP. They weren't reasons FOR CESA, they were reasons AGAINST shared air and they had no substance. Here are a couple:

Buddy proximity: Scenario indicated this was a competent buddy team. Competent buddies are accessible.

Inadequate gas supply for two divers: Scenario indicated this was a competent buddy team. Competent buddies plan their dives and include a reserve gas supply which is adequate to get both buddies to the surface.

Safety stops were brought into the discussion to support the idea that shared air is a better option than CESA. Many have chosen to dwell on the 25' used for this scenario, but have yet to define a depth which they would concede to the benefit of sharing air over CESA. I have to wonder if they see any benefit at all in doing safety stops.

We have not even touched on the impact of CESA on the buddy team. Some CESA advocates indicated that they would signal their buddy, but those same people cited buddy separation as one reason for doing CESA. Hard to signal a buddy you are not in contact with, no? This is not they type of behavior I would associate with a competent buddy. It's solo mentality and that's fine for solo diving, but it's not diving as a buddy team.

Despite the twists and turns, 93% of those responding to the poll understand the benefits of shared air over CESA. None of them indicated CESA would kill you.

 

[ReefHound]

Me I prefer the stop, think and choose the best strategy based on the situation at hand.

Yep, and sharing air allows you way more time to stop, think, and act. CESA requires an almost immediate response and once you initiate it all other options are likely lost. On the other hand, you can abort a shared air ascent if it isn't working for some reason and go to the CESA.

Obviously, the assumption is that you can easily get to your buddy or he to you. A shared air ascent is not an available option otherwise.

I think everyone understands that situations vary and you will have to choose the best strategy for the situation. All I'm saying is that the thought process will (hopefully) be to first look to my buddy and decide if I can easily make it to him, if not then of course I'm going on up. If my buddy is below me he'd better be very very close because down is the wrong way to be going if you're OOA.

I will say that I do understand the point of those who prefer the CESA in that a wrong choice can really screw the pooch so if you *know* you can make the surface with a CESA why risk trying to reach a buddy and finding out you can't for some reason? The immediate crisis is lack of air and bubbling is irrelevant if you don't get to air in time.

 

[Hank658]

Going back to the original scenario and assuming that your competent buddy has an octo available a shared air ascent works just fine. As to a safety stop in this scenario, well I'm even going to touch on that one.
With my regualr buddy I know her gear has been maintained and we know how to do the drill. I had an o-ring issue on one dive and we both made a calm shared-air ascent from 60', with a safety stop.

When it gets to be not so clear-cut is when you add in all the variables. How well do you know your buddy and how responsive to you are they? If my competent instabuddy got involved in something and allowed about 15'of separation between us then I do not know if I would expend my energy swimming to him to take the chance that his gas supply is sufficient and that his octo breathes better than a snorkel at 25'. In that case I might just make a CESA.

Also, if we are talking competent buddy teams then I must assume an equipment malfunction of some kind. If not and I am very low on air (due to 'user error' and not checking my guages) then how do I know my buddy has enough gas for the both of us?

In short, a shared air ascent can be fine, assuming both buddies are on the ball and calm enough to make the drill almost routine. If on the other hand there are questions about the buddies training, gear maintenance or ability to 'stop, think, act' for lack of a better term, then I might vote for going it by myself as opposed to possibly putting two people in a situation that can go from bad to worse very quickly.

 

[bfw]

The reason a buddy breathing ascent is considered dangerous is that most people lack competence, and a certain phenomenon that has happened all too many times - diver runs out of air, buddy breathes from 100 ft up to about 15 feet, amid the stress and then the relief that the "crisis" is over, decides "I can make it from here" and does a CESA from there, but with all the other things going through their mind, holds their breath.