Ascending too fast

[TSandM]

This is the problem with the concept of "no deco" diving. ALL dives include some decompression . . . in no-STOP diving, the decompression is built into the ascent rate. Exceed the prescribed ascent rate of the model, and you are not doing the decompression the model calls for. If you are a long way from the no-stop limit, that probably won't matter, but if you are very close to it, it might matter a great deal. Recreational diver DCS is heavily skewed to type 2, and this is felt to be related to the fast compartments, which load very quickly at depth. Thus one might theorize that rapid ascents from significant depth would predispose to the most serious form of DCS, which is central nervous system damage.

On the other hand, the most LETHAL risk of a rapid ascent is arterial gas embolism. People who suffer this are often in arrest at the surface, and are not resuscitated. This is felt to be associated with rapid ascents with a closed glottis.

 

[Mustard Dave]

Yes, but I said at least. Which means that you'll usually have time to get to the oxygen and call for help, or at least call for help.

Of course, but how many cases have we had of people getting bent from ascending at 18m/min well within NDL? PADI taught that until maybe 2 years ago, I wasn't diving then but it's still what is in my book. And I don't think there have been that many issues with it...

Ascend slowly whenever possible is my message, and keep an eye on your gauges. But don't become paranoiac because you went to 18.1m or because your computer said you have 5 minutes NDL left and you skipped a safety stop due to whatever good reason there is.

Sorry, I did misread the 'at least' comment. You should have time to call for help, however, a lot will depend on the proximity of the boat.

I am not trying to make people paronoid about the risks - DCI incidents may be less common on shallower dives that are within NDLs, but your post could read like the risks are trivial, which I'm sure was not your intention. I'm sure we can agree that the subject of the video should have done more to stop himself getting into that situation, and it is something we should all avoid.

 

[DivemasterDennis]

Somewhere in this conversation let us add this point: There is no reason, absent equipment failure, to run out of air. We were all taught to monitor our breathing gas constantly. Conversations about what bad things can happen if you run out of air should remain theoretical if we all just pay attention. One thing is for certain, nothing good comes from an out of air situation. At best nothing bad does either. Please, everyone, look at your gauges regularly. Don't wait for a DM to ask you, don't assume if other divers are fine on air you are too. This is really basic safety.
DivemasterDennis