Ascending too fast

[mikeynl]

Almost feel silly for asking this question, but anyway ... came across a video of someone who was on a drift dive, got a bit behind and then realised he was out of air and needed an emergency ascent. Someone said his ascent was too fast and that it could have caused the bends. I wonder tho, if you really need to surface fast, your reason to not to go too fast in such a case is mainly to avoid barotrauma, not the bends, is it?

 

[jboneng]

A safe ascent rate is to avoid the bends, having open airways is to avoid lung rupture. The recommended ascent rate in a O.O.A whit no buddy and no backup gas, depends on the situation like from what depth?, any deco-obligation?, is the lungs full of air or is it no breathing gas left in the lungs and so on. In any case, it is better to be in a hyperbaric chamber than in a coffin.

 

[mikeynl]

It's this video I'm talking about: https://www.youtube.com/watch?v=XujePQIafRM&index=21. I'm wondering about the remark by Jack Trevally who says "Your ascent was much too fast. You could have gotten bent." In my opinion getting the bends would not be your main worry in such a situation.

 

[Patoux01]

If you have no air and no buddy available, you don't care about a bend.
At the surface you can breathe, a bend will show up (if one should) in at least a few minutes, get O2, call for help, you might get hurt, it could be painful yes, but you should live.
If you stay under, you'll drown, and then there's almost no saving you.

Also, usually those dives are well within NDL and you probably won't get bent doing a too fast ascent. On deco dives, this wouldn't happen so don't bother thinking about "what if I had deco obligations?".

 

[mikeynl]

So that remark on going to fast cos "you could have gotten bent" is nonsense, right?

 

[Mustard Dave]

If you have no air and no buddy available, you don't care about a bend.
At the surface you can breathe, a bend will show up (if one should) in at least a few minutes, get O2, call for help, you might get hurt, it could be painful yes, but you should live.
If you stay under, you'll drown, and then there's almost no saving you.

Also, usually those dives are well within NDL and you probably won't get bent doing a too fast ascent. On deco dives, this wouldn't happen so don't bother thinking about "what if I had deco obligations?".

I agree that given the choice of drowning or getting bent, the later is preferable as it fan be fixed, but smptoms of a bend can take longer than a few minutes to show up.

Every dive is a deco dive (the only difference is you don't have to make stops) - a safe rate of ascent is always important and you can get bent on dives that are within NDLs.

The best thing the diver in that video could have done was not get into that situation to begin with.

 

[Peter69_56]

So that remark on going to fast cos "you could have gotten bent" is nonsense, right?

The remark is correct. He had 2 risks, the first was getting bent from a too fast ascent (regardless of whether he had to stop for deco or not), the second was out of air (the bigger risk).

As others have said here, if you are seriously out of air (not just low and nervous), you need an ascent rate to get you to the surface or to someone with air, regardless of the fact that you might get bent. Getting bent is potentially fixable, out of air at depth is terminal.

So to answer your question "YES he could have gotten bent, but if he was well within his NDL then the risks are somewhat less". the deeper the dive and longer you have been down, the greater the risk at getting bent on a fast ascent.

 

[Patoux01]

I agree that given the choice of drowning or getting bent, the later is preferable as it fan be fixed, but smptoms of a bend can take longer than a few minutes to show up.

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.

Every dive is a deco dive (the only difference is you don't have to make stops) - a safe rate of ascent is always important and you can get bent on dives that are within NDLs.

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.

 

[jboneng]

So that remark on going to fast cos "you could have gotten bent" is nonsense, right?

No, ascending to fast can make bubbles expand to critical diameter faster than you can off-gas to keep them below that threshold, that can lead to the bends, the main concern with a fast ascent rate is the bends and not the barotrauma, ofcourse, if there is zero bars left in the tank and the diver panics and closes his respiratory tract, there will be a risk for lung barotrauma.

 

[Hickdive]

Could he get bent? Yes, every dive carries that risk but from 18m and well-within no decompression limits the risk is minimal.

Could he have suffered damage to his lungs? Yes but provided he breathed normally or exhaled on ascent again the risk is minimal. Speed is only a risk factor for barotrauma if you fail to expel gas from your lungs faster than it is expanding. Take a lungful of air a 3 metres, hold it and ascend to the surface at 3m/min (most people can hold their breath for at least that long). That's about 1/3rd of the recommended maximum ascent rate but you'll still burst your lungs.

Could he have drowned? Yes, running out of air underwater carries a high risk of drowning.

Of all the risks the diver was exposed to during his incident drowning was the most likely to kill or injure him, followed by pulmonary barotrauma and then, a long way behind, being bent.