Blood Pressure Under Water

[dmaziuk]

It may seem dumb to you, but for a very large number of people responding to threads about how deep you can do a CESA, the primary factor is your ability to hold your breath. It does not seem dumb to them. That's the problem.

ObNitPick: I can hold my breath with the airway open while swimming 25 yards underwater, so it's not always a contradiction.

More to the point: as you say, the way CESA is/was taught in OW is wrong. And I don't know that it can be taught "right" either: it's both difficult (need body of water deep enough) and risky (students may blow their lungs).

 

[boulderjohn]

ObNitPick: I can hold my breath with the airway open while swimming 25 yards underwater, so it's not always a contradiction.

More to the point: as you say, the way CESA is/was taught in OW is wrong. And I don't know that it can be taught "right" either: it's both difficult (need body of water deep enough) and risky (students may blow their lungs).

Possible changes:
1. Emphasize to students that they are not getting any benefit of expanding air, as they would on a real ascent.
2. Emphasize to instructors that it can be faster than 60 FPM--I have assisted in classes in which students failed the exercise for doing the 30 feet in 27 seconds.
3. Do not fail students for taking a breath in the last seconds; in fact, reward them. Make sure they understand that the regulator that failed to give them air at depth in an OOA situation will give them air as the ambient pressure decreases. This shows they understand that this fact. This is not mentioned anywhere in the curriculum, and I would bet most instructors don't know it. I argued this with PADI several times in the past. Their response is that although the overwhelming majority of these ascents will be in OOA situations, it is remotely possible that it could be a failed regulator, so we need to train students for an ascent for a failed regulator rather than for an ascent in an OOA situation.
4. Show films of US Navy submarine escape training, in which they are taught to exhale all their air before they begin the ascent.

Want to hear another example of how absurd it is? When I my instructor examination, we all had to demonstrate the horizontal CESA. We started at the "deep" end of the pool, which was about 4 feet. We ended at a depth of about 2.5 feet. We all had our knees brush the floor at the end. We all got docked a point for losing buoyancy after we had exhaled for 30 seconds. Note that in a real CESA, you are supposed to dump air as you ascend to keep from becoming too buoyant and ascending too fast.