inhaling/exhaling from underwater air pockets

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ballastbelly

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in the scene from the Big Blue, where Enzo freedives into the flooded ship to save the scuba diver,
had there been an air pocket in a compartment (say 5m deep), could the freediver rest in it & breathe, obviously exhaling it in bubbles on his way up?
could the scuba diver he just rescued do the same?

does the human diaphram muscle strength have a limit on the depth one can exhale?
thanks
b
 
Remember, an air pocket at depth is at the same ambient pressure as the water around it (else it would collapse). So the person with his head in the air pocket experiences no increased work of breathing.

There are a lot of reasons not to breathe out of trapped air pockets, one of the greatest of which is that you don't really know what the gas is that is forming the pocket. But mechanically, it is quite possible, and people have survived being underwater by doing so.
 
This guy survived in an air pocket in a shipwreck for three days.

[video=youtube;iKL11BavG0U]https://www.youtube.com/watch?v=iKL11BavG0U[/video]
 
During WWII, the US submarine Tang's last torpedo made a circular run and hit the rear of the sub. One of the crew in the conning tower escaped, stopping in an air pocket on the bridge long enough to speak with another crewman. He then made a blow and go ascent and was eventually captured with the other survivors.

ESCAPE FROM THE DEEP by Alex Kershaw is a good account. You can also read the actual Tang patrol reports here:

Submarine War Patrol Reports
 
The others have answered questions about air pockets at depth. The other question you had was: "does the human diaphram muscle strength have a limit on the depth one can exhale?"

As has already been said if you are breathing air at ambient pressure (e.g. from a gas pocket or from your regulator) then there is no "
strength" required to exhale.

It is a different story if you are holding your breath from the surface and trying to equalise at depth. There is a limit to the depth at which the commonly taught Valsalva equalising technique will work (essentially using your diaphragm to force air from your lungs to your eustachian tubes to equalise). This is because you never completely empty your lungs when breathing out - generally you exhale a maximum of 75% of your lung volume and, as your lungs compress they get down to this "residual volume" and your diaphragm is not flexible enough to be used to compress your lungs any further to allow for equalising using the Valsalva technique.

To go beyond this "residual volume" (i.e. be able to equalise deeper when breath hold diving) you need to increase your diaphragm flexibility (which has limits) or learn other equalising techniques (search for Frenzel and "mouth fill" and/or Frenzel Fattah for more on this).

Many people hit the limit of diaphragm flexibility between at around 30m (when their lungs are 25% of normal size). For me I struck this at 36m initially and am now practicing "mouth fill" equalising to get to round 40m - although I haven't mastered it to be able to do it consistently. (A retired Olympic and Commonwealth Games swimmer I know had a very flexible diaphragm and pretty much got to 40m before hitting his limits without using the mouth fill technique).
 
If you dive the wreck of the Kittiwake Grand in Cayman, you can go into a recompression chamber which is still onboard and there is a sizeable air pocket inside it (comfortably enough for three divers to have a conversation). But if you inhale the air is pretty fetid, and has a very high CO2 content. Not recommended to keep breathing it for any length of time - suck on your regulator whilst waiting for your wife to finish her sentence.
 
If you dive the wreck of the Kittiwake Grand in Cayman, you can go into a recompression chamber which is still onboard and there is a sizeable air pocket inside it (comfortably enough for three divers to have a conversation). But if you inhale the air is pretty fetid, and has a very high CO2 content. Not recommended to keep breathing it for any length of time - suck on your regulator whilst waiting for your wife to finish her sentence.

Come on now, ... you really want him to find out what it feels like to run out of air??
 
Well, any port in a storm (emergency with no better alternatives), I suppose, but I'd worry about both the oxygen content and CO2. The amounts are proportional to the partial pressure of the water in contact with them and vice versa - Henry's Law. At depth, you are well below the rich 21% oxygen atmosphere, and oxygen is poorly soluble in water. In fact, if you've ever kept an aquarium, you know people use filter discharges or air stones to circulate the water to prevent oxygen depletion below the surface.

So, let's say you do a minor penetration wreck (or cavern) dive and find an overhead concavity where air's collected from other divers' exhalations. If you were taken by the novelty and swam up to breathe in it for a few minutes, to see what it was like, I wonder what the odds are you might pass out?

Richard.
 
Seems I read that the fellow who survived in the sunken boat mentioned above was able to do so because the sea water absorbed the CO2, keeping the air breathable much longer than expected.
 
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