DCS & free-diving

[tamarinda77]

Is it possible to get DCS from free-diving? (as opposed to scuba)

 

[Soggy]

No...The air taken in at the surface is at 1 ATM and absorbs into the tissues as such.

People have done breath-hold dives to over 500 ft.

Theoretically, at some point, our lungs/ribs would collapse under the extreme pressure since the difference in ambient pressure and the interior pressure are so extreme.

EDIT: This is only true with a diver doing a single freedive and no excess buildup of N2 from previous freedives/scuba dives. Otherwise, yeah...you can get bent.

 

[BillP]

Yes, tamarinda77, it is possible to develop DCS from repetitive freedives, but it would be very unlikely in a typical recreational freediver.

Symptoms of DCS have been reported in professional pearl divers who make multiple freedives, for example. See:

http://www.ncbi.nlm.nih.gov:80/entr...eve&db=PubMed&list_uids=1490974&dopt=Abstract

for an explanation of the mechanism.

The risk in the recreational diver would theoretically be increased if they did freedives immediately after scuba dives.

Scubadoc has a good article at:

http://www.scuba-doc.com/taravana.html

 

[rmediver2002]

We had one diver in Panama City about six years ago who was making free dives to 100 fsw spear fishing after finishing up some no "D" but close SCUBA...

He did get bent from it... with the nitrogen already buit up in his system he pushed over the edge on the additional decents... The biggest problem is actually the rapid ascent though...


I have heard a rule of thumb is spend at least as much time on the surface between free dives as you do on the breathhold...

Good question!!!!

Jeff Lane

 

[rcohn]

AaronBBrown once bubbled...
No...The air taken in at the surface is at 1 ATM and absorbs into the tissues as such.

People have done breath-hold dives to over 500 ft.

Theoretically, at some point, our lungs/ribs would collapse under the extreme pressure since the difference in ambient pressure and the interior pressure are so extreme.

I believe the +500 ft dives are very close to the NDL at that depth and they may need to take some precautions if they go much deeper.

The chest doesn't collapse because the lungs fill with fluid. Originally the doctors predicted lung collapse if freedivers went below 100 ft.

Ralph

 

[Soggy]

I understand how multiple/repetitive free dives or freediving after SCUBA (dumb) could cause DCS, but not a single breath-hold dive.

Gases (air) under pressure dissolve more readily in fluid (blood), so as a freediver repetitively goes under, there could be a build up of nitrogen over time in the tissues...as we know, on-gasing is quicker than off-gasing, so on ascent, not all of the N2 would escape the freediver's tissues.

However, on a single breath-hold dive, there is only enough nitrogen in the lungs as one can get from a single breath at 1 ATM (i.e. PPN2 of .79). Perhaps there is enough N2 in one breath at 1 ATM to cause mild DCS at extreme depths, but that seems implausible.

My initial response was certainly overly brief and didn't cover different scenarios....still, it is highly unlikely that a typical recreational freediver would reach depths where DCS could be an issue, unless they had been on SCUBA previously during the day.

 

[Nessie]

@AaronBBrown
Sorry I don´t agree to you. I t doesn´t matter that much how often you breathe but how much time under a certain pressure is given to absorb the nitrogen. And at depth the lungs become squeezed, so the partial pressure of the nitrogen increases. And the lungs contains about 5l nitrogen ar surface. Besides that you can not use the decompresion limits given for scuba divers as a free-diver does not ascent with the recommended ascent rate.

 

[Soggy]

Nessie once bubbled...
@AaronBBrown
Sorry I don´t agree to you. I t doesn´t matter that much how often you breathe but how much time under a certain pressure is given to absorb the nitrogen. And at depth the lungs become squeezed, so the partial pressure of the nitrogen increases. And a lung contains about 5l nitrogen.

What matters is the amount of N2 dissolved in the system -- i.e. how saturated the tissues are. The question is this: Is 5L of dissolved N2 enough to come out of solution (supersaturated) in our tissues at 1 ATM? I don't know the answer.

Also, while the lungs will get squeezed, our ribcage will prevent much of that squeeze, so I don't believe the partial pressure will ever get very high...I'm not sure of that, though. Clearly, the entire volume of N2 is not going to move into our tissues, so the actual surface volume of air will be somewhat less.

Besides that you can not use the decompresion limits given for scuba divers as a free-diver does not ascent with the
recommended ascent rate.

I wasn't using the NDL for SCUBA...I was merely saying that it's a bad idea to freedive after SCUBA, since there is already a buildup of N2 in the system.


EDIT: fixed my volume numbers

 

[WreckWriter]

Agreed that a SINGLE free dive is very unlikely to cause DCS but multiple deeper free dives over a period of time definately can, I've seen it done.

Tom

 

[Nessie]

No 4 l
Because there is a difference between the volume of your lungs (which is something about 7 liters) and the volume you can breathe in ( sorry, do not know the English terms).