Why is inhaling while ascending safe, if breathing holding will cause lung over expansion?

[emoreira]

I have held my breath on ascent while scuba diving a few times (I was super stressed one time and another time I must have thought I was freediving). Anyway, I think if you are healthy and not completely panicked, you will begin to feel a fullness in your lungs and (unless you try otherwise) you will just naturally exhale. Definitely not something to replicate or test, but if you remain reasonably relaxed you should probably be OK. As long as the air way is open, even a little, excess pressure should be vented before it can build up.

Also remember, the expansion rate is not that great until you get really shallow, I just always exhale for the last 3-5 feet, I think.

I found this video, it shows a diver getting an injury. Very interesting I thought. Freediving and breathing compressed air can be dangerous if you forget why your lungs are burning, I guess.

Those air bells are a death trap.

 

[Nitrox_DiverNY]

Exactly.

I actually have a really fun lecture that I give called "The History of Aspiration" talking about how the airway evolved to keep out everything that isn't supposed to be in the lungs. A non-trivial evolutionary challenge for the 4 classes of air breathing vertebrates. I'm working on getting the video of this talk on line, happy to post it once I get it up and running.

It's not every talk that covers both pediatric airway surgery AND how humpback whales do bubble net fishing...!

View attachment 751352

would love to watch the video if you posted it on ScubaBoard, very cool

 

[Nitrox_DiverNY]

I have held my breath on ascent while scuba diving a few times (I was super stressed one time and another time I must have thought I was freediving). Anyway, I think if you are healthy and not completely panicked, you will begin to feel a fullness in your lungs and (unless you try otherwise) you will just naturally exhale. Definitely not something to replicate or test, but if you remain reasonably relaxed you should probably be OK. As long as the air way is open, even a little, excess pressure should be vented before it can build up.

Also remember, the expansion rate is not that great until you get really shallow, I just always exhale for the last 3-5 feet, I think.

I found this video, it shows a diver getting an injury. Very interesting I thought. Freediving and breathing compressed air can be dangerous if you forget why your lungs are burning, I guess.

That is a good point about the last 5 ft being a big change, do you think it is common practice for other divers to just exhale in those last few ft as well? So say you are at 10ft on a mooring line, you would ascend a foot or two while exhaling then stop and inhale to you made it back to the surface?

Ill have to check out that video later, thanks for sharing

 

[boulderjohn]

That is a good point about the last 5 ft being a big change, do you think it is common practice for other divers to just exhale in those last few ft as well? So say you are at 10ft on a mooring line, you would ascend a foot or two while exhaling then stop and inhale to you made it back to the surface?

Ill have to check out that video later, thanks for sharing

Ascend very slowly over the last 15 feet or so, breathing normally.

 

[inquis]

That is a good point about the last 5 ft being a big change, do you think it is common practice for other divers to just exhale in those last few ft

Because it's a big change, best practice is to do it slowly -- probably too slow to just exhale. I'll take perhaps 30 seconds for the last 2 meters (6 ft). Whether that's common practice is another story.

 

[Nitrox_DiverNY]

I just want to address the implication that if the instructor did not explain this in the normal flow of the course, the instructor must suck.

The OW course strongly emphasizes that divers should never hold their breath and should continuously breathe. The is what divers need to know. They do not need to know WHY inhaling does not create the same problem as holding the breath. If they are curious and ask exactly the way it was asked in the thread, the instructor should be able to explain it, but that does not mean it should be part of routine instruction.

In instructional design, the goal is to make sure students absolutely know the essential learning points and are pretty darn good on items on the next lower level of need. Once you get down to the items that would be classified as "nice to know," you have to question why you are teaching it. Interference Theory teaches us that time spent learning the things we don't need to know interferes with our ability to learn the things we do need to know.

For example, new OW students need to know about pressure changes upon descent, and that is a standard part of OW instruction. Students are not, however, typically required to know that it is called Boyle's Law, because they don't need to know that.

Another good example is modern first aid instruction. I taught first aid more than 50 years ago, and the standard first aid class was far, far more complete than the standard first aid course today. That is because the people designing standard first aid courses determined that they were teaching too much, and students were not performing first aid when it was needed because they could not remember everything. They therefore dropped the stuff that was less critical in the hope people would remember the critical stuff and use that knowledge when needed.

that was very well said, and I do agree with you about the difference between the need to know and the questions that go above the basics. The instructor did explain the basics but in retrospect it was in a horrendously rushed time frame so I didn't really have these follow up questions to ask. sadly I did other classes as well with the same instructor

In my opinion padi AOW needs a big update to be much more in-depth about dive theory and nuances, it was a big let down but might take it again with a new instructor. But that is a conversation for another I suppose

 

[BlueTrin]

Don’t take AOW again, just go diving.

You can do either a different speciality or go for an intro to tech

 

[johndiver999]

That is a good point about the last 5 ft being a big change, do you think it is common practice for other divers to just exhale in those last few ft as well? So say you are at 10ft on a mooring line, you would ascend a foot or two while exhaling then stop and inhale to you made it back to the surface?

Ill have to check out that video later, thanks for sharing

Breathing normally for the final ascent is probably better advice. I just like to exhale for the last 10-20 seconds (few feet, not 10) of the ascent. You are over thinking this. The only real danger might be when hanging on a fixed anchor line in huge swells that are going over your head. That could cause problems if your airway is closed.

As long as your air way is open and you have no physical defects, you can ascend tremendously fast with little chance of lung injury. Again, don't try to test this!

And I agree about not retaking AOW, go diving hopefully with an experienced buddy and ask questions here.

 

[Belzelbub]

That is a good point about the last 5 ft being a big change, do you think it is common practice for other divers to just exhale in those last few ft as well? So say you are at 10ft on a mooring line, you would ascend a foot or two while exhaling then stop and inhale to you made it back to the surface?

No, I don’t think it’s common practice, but it is a good practice. That last part of the ascent is going to be where you are most buoyant. Any air in compressible vessels will be at near surface volume, so exhaling can help to slow the ascent in those last few feet as well as making sure the airway is open.

I don’t think it’s common practice because I don’t think the expansion rate is well understood among recreational divers. I’ve seen people on here unclear that the greatest risk of lung over expansion is near the surface. And that’s from people on SB, who I would guess to be at least inquisitive about diving. The vast majority of divers aren’t here, and might not be as curious to dig deeper. They may understand not to hold their breath, but maybe not precisely why, and where it’s most critical.

 

[Nitrox_DiverNY]

Breathing normally for the final ascent is probably better advice. I just like to exhale for the last 10-20 seconds (few feet, not 10) of the ascent. You are over thinking this. The only real danger might be when hanging on a fixed anchor line in huge swells that are going over your head. That could cause problems if your airway is closed.

As long as your air way is open and you have no physical defects, you can ascend tremendously fast with little chance of lung injury. Again, don't try to test this!

And I agree about not retaking AOW, go diving hopefully with an experienced buddy and ask questions here.

thanks for the help!