buddy breathing & free diving

If you free dive at great depths and say you have scuba divers around you...what if you, around 400 ft, had trouble...I heard that a scuba diver can't give you a breath of their O2 and pretty much youre out of luck..Is that true and if so what is the physics of it?
:icosm02:

They technically could give you a breath of their air, but you likely wouldn't make it. There are several things to consider. The air from the scuba diver will be compressed, so if you tried to surface without being very careful to exhale the whole time you would get a lung over-exapation injury, which could kill you.

Next thing, you would be hard pressed to find any divers at 400ft. Even highly trained technical divers will rarely go below 300 ft. Then the gas that they are breathing would likely kill you at the surface as it would have too low an oxygen level to sustain life. Deep divers use a mix of air that has a low percentage of oxygen so that they don't get O2 poisoning at high pressures. Deep free divers don't have to worry about his since they are not down for very long and a single breath would have too little O2 to cause this condition as far as I know.

I think there could be other problems as well, but I'll have to think about it.

Matt

Welcome to the board.
400ft...you like it deep, that’s well past the realm of normal scuba diving. I take it your not a diver based on the question.
The short answer is it can be done safely but the freediver had better know what is involved or they are dead.
The first main reason this is not typically done is due to the expansion of gas as the freediver ascends. At depth the scuba diver is breathing air (gas blend actually, at those depths air itself is unsafe to breath) at considerably higher pressure than at the surface. At 400ft that works out to a little less that 180psi but because the water pressure is also around 180psi the differential pressure between the water and the gas in his lungs stays the same as it does on the surface thanks to the divers regulator. There is no problem with the freediver breathing the same gas at depth. The problem comes when he starts to ascend. As he rises in the water column the pressure around him starts to decrease and consequently the differential pressure between the inside of the freedivers lungs and the out side water begins to increase. IF the diver does not allow the expanding gas to escape as he ascends, his lungs will expand to the point they rupture....a very ungood thing. This takes very little change in the water column. A breath off of a scuba divers reg at the deep end of a pool is just about as dangerous, lung ruptures are possible with only a few feet of depth change. That’s why scuba divers will not allow snorkelers to grab some air off their regs. If the freediver does allow the gas to escape as it expands, the lung over expansion does not happen and he should make it back up fine. Expanding gas is not normally a problem or a concern to freedivers as they start with a given amount of air in their lungs, it compresses as they dive and more importantly, it expands back to the same volume the diver started with. As scuba divers we are trained to never hold our breath otherwise we would be injured or killed by the same expansion of gas. There are other reasons it’s not a good idea but this is the biggie.

First off, at 400 ft the scuba diver is not breathing 02.

Second, this earlier thread covers what you ask, and sorry Herman, but its unlikely the freediver could take a breath from any compressed source at 400ft.

http://www.scubaboard.com/showthread.php?t=141304




~Marlinspike

There is a guy named Pipin who has a "two breath" depth record at around 500 feet I think. He survived, perhaps he could explain the physics of it all and the reality of what is possible. It's really an extreme "bounce dive" you're talking about.

ZAquaman:

There is a guy named Pipin who has a "two breath" depth record at around 500 feet I think. He survived, perhaps he could explain the physics of it all and the reality of what is possible. It's really an extreme "bounce dive" you're talking about.

Click to expand...

That guy Pipin is a hack whose careless methods killed his wife. Again, get a clue.

~Marlinspike

Pipin did do these 2 breath dives more as a stunt then anything else. Pipin has been bent on more than one occasion for doing these kinds of stunts as well.

Bottom line is - don't breathe compressed air while freediving - if you want to breathe gas, go scuba...

YES YOU COULD TAKE A BREATH!

Of course the SCUBA diver would not be breathing O2, it would be some sort of trimix. Putting that aside, if a freediver wanted to they could take a breath off the scuba divers tanks, but if they wanted to surface, depending on how many breaths they took, would have to either a) go into decompresion with that diver or b) if they only took one or two breaths, the nitrogen or helium absorbtion would not be significant enough to go into deco and could then surface slowly rembering to exhale.

Now 400 ft is a long way to do a CESA (controlled emergency swimming ascent) but it is do able, maybe not be everyone, but by someone with the fitness it takes to dive to 400 ft could. Another thing said, if they were free diving properly they would have all the nescesary precautions taken so that this wouldnt happen.

anakin:

YES YOU COULD TAKE A BREATH!

Of course the SCUBA diver would not be breathing O2, it would be some sort of trimix. Putting that aside, if a freediver wanted to they could take a breath off the scuba divers tanks, but if they wanted to surface, depending on how many breaths they took, would have to either a) go into decompresion with that diver or b) if they only took one or two breaths, the nitrogen or helium absorbtion would not be significant enough to go into deco and could then surface slowly rembering to exhale.

Now 400 ft is a long way to do a CESA (controlled emergency swimming ascent) but it is do able, maybe not be everyone, but by someone with the fitness it takes to dive to 400 ft could. Another thing said, if they were free diving properly they would have all the nescesary precautions taken so that this wouldnt happen.

Click to expand...

:lol:

You evidently haven't done much freediving - and evidently aren't well informed about MDR.

actually i am well informed about the MDR. And i think somewhere along the lines you were miss informed. There is absolutly no reason why a conscience freediver couldnt take a breath at 400 ft off of a scuba divers tank.