CESA Question

[scubaozy]

Here is another curiosity: What do free divers do? We've got a free diving depth record of more than 800 feet. Do free divers hold their breath until they actually return to the surface several minutes later? Are they not risking decompression sickness?

Free divers diving to extreme depths, do need to decompress as well. For instance Herbert Nitsch had an unfortunate case of decompression sickness during a record attempt resulting permanent injuries.

 

[Angelo Farina]

The old days when J-valves with no SPGs were common were before my time, but apparently malfunctions were common enough with them to make CESAs common. About a decade ago, in one of the many threads on topics like this, a participant talked about a potential one regulator buddy breathing scenario at 100 feet by declaring that there is no way he would share his air with someone. An old timer instructor (Thalassamania) replied that if he were in that situation with that guy who would refuse to share air, he would calmly give him the entire BCD, tank, and regulator and then ascend next to him doing a CESA, blowing bubbles at him the whole way.

So even though I have not practiced a CEA from great depths, I have total confidence that I can get safely to the surface without too much trouble, which sadly contrasts with the divers who die after a panicked, breath-holding ascent.

The point is PANIC, not being OOA. I witnessed a number of panicked ascents, and in none of them the tank was empty or reg malfunctioning. The diver was simply thinking of being unable to breath, for other reasons (mammalian reflex after flooding or loosing the mask, closing his/her epiglottis - panic due to getting wounded accidentally - sudden appearance of a shark - CO2 intoxication causing inefficient fast breathing - tympanic membrane rupture due to improper Valsalva equalisation - etc.).
Under these panic situations, the reg is working normally. Still the panicked diver cannot breath, and often keeps the glottis closed, causing a traumatic embolism or lung rupture.
So, training the student with a not-breathing CESA (as PADI does) or with a controlled buoyant ascent while breathing (as CMAS was doing when I was an active instructor) is not the real solution: personally I think that what is required is training the students to control panic, control breathing, and control their emotions, so that they take proper action staying underwater instead of speeding towards the surface.
But this requires a 9-months long training, as the one I had in 1975, it cannot be done in a two-days weekend.

 

[boulderjohn]

Really? The scuba tank displacing the same amount of water but having less weight doesn't affect buoyancy?

Johndiver999 correctly explained it, but I want to repeat with a little more detail because this is often misunderstood.

A diver's buoyancy is determined by the entire combination of factors. Some of them are neutrally buoyant. Some are positively buoyant. Some are negatively buoyant. For two examples, the air in the diver's BCD wants to go up, and the lead being carried wants to go down. With a neutrally buoyant diver, all those factor's equal out.

In the scenario described here, the diver is out of air at then end of a dive, meaning the tank is nearly empty. If it is an aluminum tank, it would like to head for the surface, but that positive buoyancy is balanced out by negative buoyancy factors, including especially the weights being carried. The diver is neutrally buoyant.

When the diver starts to ascend doing a CESA, two things happen with respect to the gear that change buoyancy. The air in the BCD expands. The bubbles in the wetsuit (or the drysuit bubble) expand. If the diver wishes to control that ascent, the diver must dump some air from the BCD a little at a time. The cylinder's buoyancy will not change at all during the ascent, and it will not affect the changing buoyancy.

 

[boulderjohn]

personally I think that what is required is training the students to control panic, control breathing, and control their emotions, so that they take proper action staying underwater instead of speeding towards the surface.

I agree.

My more thorough analysis of what is wrong with the way we teach scuba is not so much that it fails to teach divers not to panic in that situation; rather it helps induce panic in that situation.

The horizontal CESA done in the pool requires the student to swim at a normal ascent rate for 30 feet while exhaling the entire time. What is a normal ascent rate? When I started, it was 60 FPM, meaning that a diver would need to exhale for 30 seconds to complete the exercise. Today 30 FPM is the norm, so a diver would have to exhale for a full minute to complete that exercise. Exhaling for 30 seconds is really hard for new students; exhaling for 60 would be about impossible. That is because in the CESA, there is no expanding air to help the process. When it is done in a swimming pool starting at the deep end, there is some expanding air benefit, but not a lot--the student is really only ascending about 7-8 feet.

The student then does it vertically in the open water portion of the class, but often only from 20 feet or so. this does nothing to overcome the overriding learning experience from the pool session--this is really hard! I probably would never make it in real life!

When I did my IE, the examiner told us all to interpret the word "normal" liberally. The standard was 30 feet, and no time range was mentioned. When I assisted classes before becoming an instructor, though, the norm was to get the students to as close to 30 seconds as possible He looked at his watch the whole way. If the student took only 27 seconds, he might let it go, but anything quicker than that was a failure. We did one CESA repeat after another after another before getting the whole class through the exercise.

In my 18+ years on ScubaBoard, I have seen countless threads on the CESA, and the overwhelming sense of posts is "I could only do one from very shallow depths. Deeper than that, I am toast." You even see people with some level of expert status offering the nonsensical advice to practice freediving to increase the depth from which they can ascend, as if your ability to hold your breath has any relationship to exhaling expanding air. With this representing what people think of the CESA, it is no wonder people panic in that situation.

When I teach horintal CESA, I do everything I can to do away with that fear:

• I flat out explain why the horizontal CESA is not realistic.
• I explain that they will very likely get a warning as their breathing gets harder.
• I emphasize that they can do it easily from most depths.
• I remind them that holding the breath is the worst mistake they can make.
• I tell them they will be able to get air as they ascend, so keep that regulator in the mouth!
• I don't care if they take less than 30 seconds, although no outright sprinting is allowed.
• If they inhale briefly at the end, I won't notice

 

[Superman541]

What an active and helpful Board this is!

Yup, I was nervous about CESA. Anxious. Reading through the posts, including these last few posts, above leave me with this:

Keep your wits. Pay attention. Monitor your air. Keep an eye on your dive buddy.

If/when something happens, continue to keep your wits and you should be just fine.

If necessary, do a CESA. You will likely get some additional air as depth decreases.

And if necessary, choose to be alive and injured at the surface rather than dead at depth. If you are suddenly OOA and let's say you are also winded and out of breath and must get to the surface quickly, then I guess that's what you have to do. Continue to keep your wits about you.

 

[boulderjohn]

When considering the risk of getting decompression sickness by going to the surface quickly in an OOA emergency, here is something else to think about.

If you are diving within no decompression limits and ascend at a rate of 60 FPM without stopping, it will be unlikely for you to get DCS. Ascending at 30 FPM is preferred, and safety stops on deeper dives are preferred, but a direct ascent at 60 FPM will likely be just fine.

Note the use of "likely" and "unlikely." Nothing is certain, but the likelihood of DCS with a 60 FPM ascent rate is pretty darn close to zero. Increase the ascent rate due to a CESA or buoyant ascent, and you will increase the possibility of DCS, but not to the point of likely. If you do get DCS after such an ascent, the case will likely be very mild and treatable.

Summary: If you are out of air with no possibility of sharing air, head for the surface, and don't let a glimmer of fear about DCS enter your mind.

 

[wetb4igetinthewater]

don't let a glimmer of fear about DCS enter your mind.

DCS for recreational divers beats drowning. for technical divers skipping a huge deco obligation, I'll take drowning.

 

[Boarderguy]

DCS for recreational divers beats drowning. for technical divers skipping a huge deco obligation, I'll take drowning.

I think that's the position of @Trace Malinowski too

 

[boulderjohn]

DCS for recreational divers beats drowning. for technical divers skipping a huge deco obligation, I'll take drowning.

The word huge covers a lot of ground.

In The Last Dive, Bernie Chowdhury describes his major technical diving screw up that led him to ascend directly from depth with no deco stops. It was sure a bad experience for him, but he wrote the book, he still dives, and you can discuss it with him on FaceBook. It did not go so well for the Rouses when they tried it, which is why he wrote the book.

I think that's the position of @Trace Malinowski too

I doubt it. I think that given the alternative, Trace is happier making snow on the ski slopes in the Poconos now.

 

[wetb4igetinthewater]

I think that's the position of @Trace Malinowski too

I was thinking of Rouse Sr and Jr. They really suffered