Why scuba diver can't share gas with freediver?

[rockystock1]

If the free diver keeps breathing of the reg all the way to surface he will be fine

If the free diver takes a good breath then try's to free dive up to the surface he's dead

Conversation over


Rocky

 

[Roatan Joe]

Sean, again I openly admit that I'm not an expert on the topic of freediving but I do think you might be incorrect about part of what you said. As a scuba diver your lung volume does not decrease to 25% at 30 meters because you are breathing compressed air. That is one of the big differences between freediving and scuba.

 

[jboneng]

If the free diver keeps breathing of the reg all the way to surface he will be fine

If the free diver takes a good breath then try's to free dive up to the surface he's dead

Conversation over


Rocky

He is not dead if he exhales all the way back up to the surface, as is taught in OW in case of an OOA with no buddy in sight scenario. Even if he holds his breath, the result is dependant on many factors, like how deep he was, how big sip of air he took, lung volume, mucus in lungs and soo on, the most likely outcome is that our free diver would survive, but is now on pure oxygen and on his way to the hospital.

 

[Roatan Joe]

And sorry, he's a world class freediver and freediving instructor, so I'm probably going to believe what he says until told otherwise by someone who has better credentials.

I guess it might be a combination of the fact that #1 - freedivers aren't trained for doing a CESA from 100+ ft (and neither are we) and maybe what someone else mentioned a few posts back about #2 - the lungs being compressed to such a small volume that taking a breath wouldn't be possible even if the freediver wanted to.

 

[TMHeimer]

Then there is this little problem called buoyancy control. Most free divers only become neutrality buoyant at some depth well below the surface. So even if they know how to keep their airway open durning an ascent on compressed gas, you will both end up on a free ride to the surface once they become positive.

Not a good plan for a happy ending, there are too many things that can go wrong, resulting in two victims.


Sent from my iPhone using Tapatalk

While I agree that in general this stuff is just not a good idea, I think it depends on how long the free diver breaths off the reg at depth. If it's just to get a breath or two, then a faster than ideal ascent for the free diver by himself shouldn't cause any DCS. If they ascend together, the free diver is still breathing while sharing air.

 

[Roatan Joe]

I don't see how this is any different that diving to 30m on scuba and mostly exhaling. In both cases you've got lungs 25% filled with 4 atm of air. No offense, but being a world class freediver doesn't give someone a world class understanding of the physics of pressure (for the record I am neither a world class freediver nor have a world class understanding of the physics of pressure - but I do have a decent one).

This probably explains it better than I..

"We have already seen how, for the breath-hold diver, Boyle's law predicts that compressible air spaces will shrink on descent and re-expand on ascent, and that the situation is different for scuba divers because compressed air is continuously inhaled. Even if the scuba and breath-hold diver go to the same depth and spend the same amount of time under water (e.g., one minute), the effects of water pressure are radically different on the two divers. Because tank air is inhaled at the ambient pressure, the scuba diver's lungs and other compressible air spaces do not shrink."

Effects of Unequal Air Pressures While Scuba Diving

From my limited knowledge it would seem that if a freediver continually exhaled during ascent (similar to CESA) he might survive, assuming that he was able to actually inhale a breath of air from a regulator after his lungs were compressed to very low volumes due to the pressure. But I really wouldn't expect that is something a freediver is really trained to do.. Freedivers don't breath!

 

[drrich2]

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?

Okay, with all due respect to people selling compressed air for paintball enthusiasts...

1.) Dive shops generally require a scuba cert. card to sell you compressed air. This card is taken as proof that you have been informed of the risks & methods for dealing with breathing compressed air at depth and changing depth, have demonstrated the knowledge & skill to do so safely, and are making an informed decision to receive and use this potentially dangerous product.

2.) Scuba divers are accustomed to not holding their breath.

If you happen to meet a free diver at depth, and give him gas, you have no way to definitively verify that he is scuba certified. Upon getting a breath, he's likely to break away from you & head for the surface. What do you do? Do you grab him & try to make him ascend gradually with you? A stranger could misinterpret that and try to fight you off. And this guy is trained & conditioned to hold his breath till he reaches the surface.

The only scenario in which such a thing might seem acceptable is if the scuba diver & free diver know each other, the latter is scuba certified & the former knows this, and even then, you've got a free diver who's engaged in a free dive who is used to holding his breath on the way up. Why would this scenario arise? Are we assuming a free diver who wants to free dive deeper than he safely can, and wants to plan to meet his scuba friend at the deep portion of the dive so he can get a fresh breath & do a CESA?

Richard.

 

[Roatan Joe]

If you happen to meet a free diver at depth, and give him gas, you have no way to definitively verify that he is scuba certified. Upon getting a breath, he's likely to break away from you & head for the surface. What do you do?

Richard.

Hand him a lift bag and give him the "hold on signal"? LOL.... sorry, it's late......

 

[rockystock1]

And sorry, he's a world class freediver and freediving instructor, so I'm probably going to believe what he says until told otherwise by someone who has better credentials.

I guess it might be a combination of the fact that #1 - freedivers aren't trained for doing a CESA from 100+ ft (and neither are we) and maybe what someone else mentioned a few posts back about #2 - the lungs being compressed to such a small volume that taking a breath wouldn't be possible even if the freediver wanted to.

We breath the air at the same pressure as the surrounding water,, job of the regulater


Rocky

 

[dumpsterDiver]

Okay, with all due respect to people selling compressed air for paintball enthusiasts...

1.) Dive shops generally require a scuba cert. card to sell you compressed air. This card is taken as proof that you have been informed of the risks & methods for dealing with breathing compressed air at depth and changing depth, have demonstrated the knowledge & skill to do so safely, and are making an informed decision to receive and use this potentially dangerous product.

2.) Scuba divers are accustomed to not holding their breath.

If you happen to meet a free diver at depth, and give him gas, you have no way to definitively verify that he is scuba certified. Upon getting a breath, he's likely to break away from you & head for the surface. What do you do? Do you grab him & try to make him ascend gradually with you? A stranger could misinterpret that and try to fight you off. And this guy is trained & conditioned to hold his breath till he reaches the surface.

The only scenario in which such a thing might seem acceptable is if the scuba diver & free diver know each other, the latter is scuba certified & the former knows this, and even then, you've got a free diver who's engaged in a free dive who is used to holding his breath on the way up. Why would this scenario arise? Are we assuming a free diver who wants to free dive deeper than he safely can, and wants to plan to meet his scuba friend at the deep portion of the dive so he can get a fresh breath & do a CESA?

Richard.

It is not that weird to think a freediver might like to swim down to a his buddies who are scuba diving, take a few hits from a regulator, maybe the octopus, hang out for a minute or two and then ascend alone. It is not really difficult and it is not some great feat to ascend slowly and release air on ascent.

It is however potentially dangerous from a lung over expansion perspective. Also, if as described earlier, if the freedivers lungs are compressed past the point of a complete exhalation, then they might not be able to inhale at depth. That later part, I wouldn't really know about because I can't snorkel that deep- but I do know that 60 or 70 feet is not an issue.


I've taken a hit or two from a regulator many times and then went up, but I doubt anyone (either scuba or freedive trained) thinks it is a good idea. I won't let my kid do it, but I am 99.9% sure he COULD do it with no problem.

It is kinda like doing a scuba entry from an elevated tree stand using a rope swing, just because it might be fun and we can do it, doesn't mean we should do it..