Gas / lung expansion questions

I'm currently enrolled in the OW course, and my experience includes the discover scuba course with two OW dives.

Had some general questions while studying, hopefully I can find answers here:

1. From what depth does an emergency ascent become unsafe? Both in terms of exhaling expanding gas as pressure decreases, and from a nitrogen standpoint during a no decompression limit dive.

2. During an emergency ascent, going straight for the surface, with no safety stop, do you continue to breathe if you have air supply with enlongated period of exhalation, or do you only exhale, not running out of expanding air until hitting the surface? Without air I imagine you exhale, but do you slowly exhale or get as much air out as possible? I guess what I'm wondering is, while exhaling, will the expanding gas take care of itself as long as the airway path is open or is must you vent at a specific rate?


3. If an unconscious, not breathing diver is retrieved at depth and brought to the surface by another diver is lung expansion a concern? Will the excess air escape by itself or tear the lungs to pieces? If they have aspirated water, near drowning, will there be remaining gas in the lungs or will the water prevent lung expansion injury?

All I got for now, appreciate any replies.

cyrilgrey:

I'm currently enrolled in the OW course, and my experience includes the discover scuba course with two OW dives.

Had some general questions while studying, hopefully I can find answers here:

1. From what depth does an emergency ascent become unsafe? Both in terms of exhaling expanding gas as pressure decreases, and from a nitrogen standpoint during a no decompression limit dive.

Click to expand...

I don't know what the books says so don't use my answer as the only source for the test. but if it's a no decompression dive you should be able to make an emergency ascent from any depth that you are at.

2. During an emergency ascent, going straight for the surface, with no safety stop, do you continue to breathe if you have air supply with enlongated period of exhalation, or do you only exhale, not running out of expanding air until hitting the surface? Without air I imagine you exhale, but do you slowly exhale or get as much air out as possible? I guess what I'm wondering is, while exhaling, will the expanding gas take care of itself as long as the airway path is open or is must you vent at a specific rate?

Click to expand...

If you have air then you just breath normally. If you have only the one breath then you simply keep the airway open...I think the suggestion is to hum or blow tiny bubbles.

3. If an unconscious, not breathing diver is retrieved at depth and brought to the surface by another diver is lung expansion a concern? Will the excess air escape by itself or tear the lungs to pieces? If they have aspirated water, near drowning, will there be remaining gas in the lungs or will the water prevent lung expansion injury?

All I got for now, appreciate any replies.

Click to expand...

I'm not sure on this one. If I found such a person I would be trying to compress his chest if I didn't see air bubbles coming out. I can't remember what the exact answer to this was from rescue class. Certainly it would be a concern.

I'm sure you will get other more complete answers.

cyrilgrey:

I'm currently enrolled in the OW course, and my experience includes the discover scuba course with two OW dives.

Had some general questions while studying, hopefully I can find answers here:

1. From what depth does an emergency ascent become unsafe? Both in terms of exhaling expanding gas as pressure decreases, and from a nitrogen standpoint during a no decompression limit dive.

Click to expand...

If you are doing an emergency ascent it usually means that you ran out of air ... in which case you must attempt it from whatever depth you are at when that happened. The depth at which it becomes unsafe varies from person to person ... there are people out there who have been trained to do this from more than 100 feet! For the rest of us, your other choice is drowning ... I think I'd not worry about what else was unsafe. Likewise, I wouldn't be concerned about any potential DCS ramifications. DCS is treatable ... drowning generally is not.

And always remember to keep the second stage in your mouth ... as you get closer to the surface the air in your second stage hose will expand, giving you just a slight bit of a breath to use on the way up.

cyrilgrey:

2. During an emergency ascent, going straight for the surface, with no safety stop, do you continue to breathe if you have air supply with enlongated period of exhalation, or do you only exhale, not running out of expanding air until hitting the surface? Without air I imagine you exhale, but do you slowly exhale or get as much air out as possible? I guess what I'm wondering is, while exhaling, will the expanding gas take care of itself as long as the airway path is open or is must you vent at a specific rate?

Click to expand...

If you have air available, then by all means continue to breathe.

3. If an unconscious, not breathing diver is retrieved at depth and brought to the surface by another diver is lung expansion a concern? Will the excess air escape by itself or tear the lungs to pieces? If they have aspirated water, near drowning, will there be remaining gas in the lungs or will the water prevent lung expansion injury?

All I got for now, appreciate any replies.[/QUOTE]
With an unconscious diver, you are always faced with a difficult decision. Most times you won't know why the diver is unconscious. But the risk of an occluded airway is far less than the risk that if you don't move the person, they will eventually drown. So the priority is to move them to the surface, where they can be treated.

The notable exception is someone who is convulsing due to oxygen toxicity. But the symptoms of ox tox are visibly noticeable, and it's unlikely that a new diver will have to deal with someone in that condition (it's usually a symptom of someone who's gone too deep on nitrox, or a "tech" diver who's breathing a very oxygen-rich mixture).

In most cases, when someone goes unconscious, their airway and jaw muscles will relax ... meaning that not only is their airway open, but you must take care that they do not lose the regulator out of their mouth.

This will all be taught to you in a Rescue class ... which, after Open Water, is a class I highly recommend for all scuba divers.

... Bob (Grateful Diver)

The essence of recreational, or "no-stop" diving, is that a direct (controlled in rate) ascent is possible from any point in the dive. This is why you are so carefully taught to monitor your depth and time and understand your no-deco limits. Once you have stayed down long enough to absorb enough nitrogen that you CAN'T safely go to the surface, you are at far higher risk, and must solve your problems underwater. That's a whole different realm of diving, requiring different equipment and a lot more training.

As Bob says, if you have gas, you continue to breathe as you ascend. If you are out of gas, you keep the regulator in your mouth. Once ambient pressure falls below the pressure in the tank, more gas will be able to exit and you may get a breath on the way up. But if you don't, you continue to exhale. The key point is to keep the airway open; if you do this, expanding gas will pretty much take care of itself, causing you to exhale a little faster if you're too slow. You don't want to exhale as much as possible right away, because you will feel less air hunger if you leave some gas in your lungs. Remember that, at depth, you have supersaturated your hemoglobin with oxygen, so you actually have several minutes before oxygen need becomes a serious problem.

An unconscious diver is a very bad thing underwater. You cannot know if the person has an open airway or not -- all you can do is try to position the head so that flexion of the neck doesn't produce a blocked airway. Aspirating water does NOT protect from lung overexpansion injury, because it would take a long time and a lot of water to saturate all the air spaces in both lungs (and then you'd have worse problems than lung barotrauma!)

The bottom line in all of this is to get some education on how to avoid running out of gas. With the exception of rare equipment malfunctions, running out of gas is entirely preventable.

cyrilgrey:

I'm currently enrolled in the OW course, and my experience includes the discover scuba course with two OW dives.

Had some general questions while studying, hopefully I can find answers here:

1. From what depth does an emergency ascent become unsafe? Both in terms of exhaling expanding gas as pressure decreases, and from a nitrogen standpoint during a no decompression limit dive.

Click to expand...

Theoretically you should be able to do this from any depth without a safety stop providing you have stayed within NDL's

cyrilgrey:

2. During an emergency ascent, going straight for the surface, with no safety stop, do you continue to breathe if you have air supply with enlongated period of exhalation, or do you only exhale, not running out of expanding air until hitting the surface? Without air I imagine you exhale, but do you slowly exhale or get as much air out as possible? I guess what I'm wondering is, while exhaling, will the expanding gas take care of itself as long as the airway path is open or is must you vent at a specific rate?

Click to expand...

Why would you being doing an Emergency ascent as if you were out of air (evacuating gas) if you are not?.... simply breath normal if you have air. I assume you're following proper ascent rates? no? If you are out of air and ascending on that last breath, YES, as long as you maintain an open airway gas will simply evacuate on it's own. Far trickier than it sounds, but easier than most imagine.

cyrilgrey:

3. If an unconscious, not breathing diver is retrieved at depth and brought to the surface by another diver is lung expansion a concern? Will the excess air escape by itself or tear the lungs to pieces? If they have aspirated water, near drowning, will there be remaining gas in the lungs or will the water prevent lung expansion injury?

Click to expand...

One of the easiest ways to ensure they pop or get an embolism is to ascend them without an open airway. They very well may, and most likely DO have air in the lungs care must be taken in bringing an unconscious diver to the surface. Conversely, no air in the lungs negates the possibility of LOE but perhaps not AGE. That is unless my understanding of AGE is flawed...

The limits for recreational diving are designed so that you can get to the surface without having to break through a ceiling. That ceiling may be a wreck, a cave, or a virtual one like a deco limit. If you've got a ceiling between you and the atmosphere, then as TSM said, you have to solve the problem underwater.

You can't solve the problem with recreational gear or training.

I would pull an unconscious person to the surface and let a medical doctor deal with any problems that arise. Chambers are better than coffins.

Also, two corpses are never better than one. If in doubt, let a recovery team get the body.

I may have misunderstood, but I think there was another implied question lurking in the background.

You asked about inhaling, and TS&M correctly pointed out that your tank is not really out of air--it just can't deliver air at the pressure you are under at your depth. You should be able to get air later on when you get shallower and have less surrounding (ambient) pressure.

I think the hidden question was whether it is safe to inhale that air during your ascent. It's a logical question. If it is not safe to hold your breath, why would it be safe to inhale? The difference is that when you hold your breath, expanding air that needs to come out is trapped because your airway is closed. In order to inhale, you must open you airway. If your airway is open, expanding air will come out. Under that circumstance, you will not want to inhale--in fact, you really can't.

If you are so out of air that you need to inhale, that means you do not have expanding air coming out, and it is safe to inhale. That is why it is safe to follow a normal breathing patter during a normal ascent.

While you've received some good and correct information, I interpreted your question #1 in another way ...

While the absolute pressure obviously decreases as you ascend, the greatest pressure differential happens between 33 ft and the surface, with the absolute pressure decreasing by 50% over that distance. So while it should be relatively safe and easy to do an emergency ascent from 33 ft, the pressure decrease from two atmospheres to one lends the possibility of severe barotrauma as the result of a gas embolism if not done correctly. In this sense, the answer to your question "From what depth does an emergency ascent become unsafe?" is "... not very deep."

Thanks guys, you answered all of my questions and some besides.

boulderjohn you're right about that first question, afraid i didn't phrase that part very well.

I'm reading as much as I in manuals, articles, here on the board and studying all of the accident and incident reports. The main purpose behind these questions is understanding of the physics behind diving. For instance, while you wouldn't leave an unconscious diver underwater, it's good to be aware that expansion is still a problem and it sounds like methods have been designed to cope with it.

Great board, going to like it here.