Why scuba diver can't share gas with freediver?

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mrdre

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I can't find the answer. The scenario is: the SCUBA diver is at 100 fsw, the free diver descends to 100 fsw, SCUBA diver shares the gas with the free diver, they both ascend sharing the gas.

What can go wrong with this? It seems that there is an opinion that this can kill the freediver, but I can't find any clear answer why and can't think of any reason why this is dangerous for the freediver. If it can be done from 100 fsw with air, can the same be done from 200 fsw with SCUBA diver using trimix?
 
The danger is that the freediver may not know that he must keep his airway open during ascent. If he hold his breath, as freedivers normally do, he is in big trouble.
 
Free divers will generally die if the don't hold their breath for the duration of the dive. Breathing from SCUBA, at 100 feet, that free diver WILL die if they hold their breath due to lung over expansion - simple as that.
 
There is no problem as long as free diver is breathing normally and ascends with the diver. The problems arise if the freediver were to take a "hit" of air and then try to make it to the surface on his own....then you are looking at possible over expansion injuries, maybe even an OOA.
 
So if a freediver is at 30 meters and his lungs have compressed down to 25% of their normal size, maybe I'm wrong but it doesn't seem like it would be a good idea to suddenly inflate them by taking a breath off of scuba. But I'm willing to learn otherwise. Watch this cool video. I asked Walid about being offered air during the video and he told me that it could have seriously injured him if he had accepted the air. I didn't question him further about why. Walid is a world class freediver..

Freedive Roatan - El Aguila - YouTube

Anyway, it's a cool video. Enjoy!
 
I see the problem with a freediver sipping from a scuba tank at 30m, then ascending like freediver while mostly holding his breath. I don't see the danger in making a controlled asent (i.e. normal for the diver) sharing air. Isn't this exactly what safety divers are for?

---------- Post added October 24th, 2014 at 10:19 PM ----------

Lots of folks posted while I was writing. Looks like we were all writing the same answer!
 
So if a freediver is at 30 meters and his lungs have compressed down to 25% of their normal size, maybe I'm wrong but it doesn't seem like it would be a good idea to suddenly inflate them by taking a breath off of scuba. But I'm willing to learn otherwise. Watch this cool video. I asked Walid about being offered air during the video and he told me that it could have seriously injured him if he had accepted the air. I didn't question him further about why. Walid is a world class freediver..

Freedive Roatan - El Aguila - YouTube

That is an interesting point, I'm not sure what the correct answer is, but I don't believe it is actually an issue.

My initial scuba training in the 1970's involved doff and don practice, with the "final exam" being a freedive into the deep end of a pool (about 20' deep, under the high dive boards). All of our gear was arranged on the bottom, including mask and fins, the the air was turned off. You take a deep breath, swim down to your tank, turn on the air take a breath, then don the rest of your gear and surface normally.

My point is that there is a fair amount of compression descending that first 20'. There were zero issues with breathing compressed air after freediving to this depth, and I am guessing this would remain true at greater depths.

But again, this is just my opinion, and it would be interesting to find out for sure; I've never really given it much thought and I could certainly be wrong.

Best wishes.
 
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So if a freediver is at 30 meters and his lungs have compressed down to 25% of their normal size, maybe I'm wrong but it doesn't seem like it would be a good idea to suddenly inflate them by taking a breath off of scuba. But I'm willing to learn otherwise. Watch this cool video. I asked Walid about being offered air during the video and he told me that it could have seriously injured him if he had accepted the air. I didn't question him further about why. Walid is a world class freediver..

Freedive Roatan - El Aguila - YouTube

Anyway, it's a cool video. Enjoy!

As I understand, the maximum lung volume is about 6 liters (achievable with a maximum inhale). A freediver has trained to increase that volume. And the maximum that you can reduce it to by forcefully exhaling is about 1.2 liters. Normal breathing works on about .5 liters going from the normal exhale volume of 2.4 liters to the normal inhale volume of 2.9 liters. I don't believe you can over expand your lungs without the aid of an external pressure change.

I believe some freediving events allow a Spare Air for emergencies.
 

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