Freediving after scuba. Any hard data?

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benha

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Folks,

Having been somewhat condescendingly yelled at by captain for doing something I do pretty regularly, I thought I'd see what the Internet had to say about freediving after scuba.

What I've found is a whole lotta people who say things like "Dude it's a horrible idea. Why would you risk it?!?!" and very little hard data suggesting either cases of DCS that can be directly attributed to the rapid recompressions / decompressions associated with freediving during a period of high nitrogen loading in one's body, or controlled studies that support well-founded conclusions.

The more scientific material I did find suggested at best that there's a potential risk - albeit a minor one - associated with mixing the two but that there's not a lot of actual data so it remains in the realm of the theoretical.

Have I missed something? Is there better data out there to help guide one's decision making? Realistically we all take calculated risks every time we jump in the water. The key is having good data to do the calculating. I'd like to get past the people who vociferously advocate extremely conservative practices in the absence of data, and get to where I can make more informed risk management decisions.

Best,
-Ben


PS - If you're wondering what I got yelled at for:
We did one 35 minute dive to 80' or so. About 40 minutes into our surface interval I got too hot to sit on the boat and swam around a bit. Dropped to maybe 30' a couple of times only to get screamed at. Seems a bit extreme to me...
 

H2Andy

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I haven't been on the board or diving for ages, so I'd love to hear from others, but I found your question interesting and did a quick search:

"Regardless of whether breath-hold diving produces VGE by itself, the concern that breath-hold diving after scuba may cause the redistribution of VGE seems rational, but the risk remains very small."

Alert Diver | Could Breath-Hold Diving after Scuba Cause Decompression Sickness?


from my diving days, I remember a strong prejudice against free diving after scuba diving, though if I recall correctly, there were no actual studies on the subject. Hope this helps
 

benha

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Yep. That's one of the items I found that was attempting to be a bit more scientific / rational about it and basically suggested there was a theoretical minor risk, but that there wasn't much data.

I'm just trying to separate lore from fact. People believe a lot of things without thinking about them. I agree with the notion that repeated recompressions/decompressions with elevated nitrogen levels could cause weird things to happen. This is especially true in light of the fact that freediving decompression rates are much faster than those associated with scuba.

I'd just like to understand it better than "seems like a bad idea to me."

I mean, lots of people believe it's a terrible idea. And yet lots of people do this all the time and have no issues. And as yet, I've never heard of someone that had an actual problem from doing it.

Trying to get more facts.
 
R

redacted

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PS - If you're wondering what I got yelled at for:
We did one 35 minute dive to 80' or so. About 40 minutes into our surface interval I got too hot to sit on the boat and swam around a bit. Dropped to maybe 30' a couple of times only to get screamed at. Seems a bit extreme to me...

Free diving during the SI is a somewhat different situation than free diving after scuba. How did you account for the decreased off-gassing for your 2nd dive?
 

H2Andy

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oh good eye ...

in that it can slow down nitrogen release off tissue?
 

Dr Deco

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In my opinion, based largely on my research at NASA, concerns muscle contractions and the enlargement of tissue bubbles. (This was also suggested by E N Harvey in 1945.) Strenuous activity following diving is to be avoided. Tissue bubbles can form (or enlarge) and result in pain. Release into the blood stream is definitely real. Limb movement is employed during Doppler monitoring to release tissue bubbles into the blood stream.
 

dumpsterDiver

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In my opinion, based largely on my research at NASA, concerns muscle contractions and the enlargement of tissue bubbles. (This was also suggested by E N Harvey in 1945.) Strenuous activity following diving is to be avoided. Tissue bubbles can form (or enlarge) and result in pain. Release into the blood stream is definitely real. Limb movement is employed during Doppler monitoring to release tissue bubbles into the blood stream.


The danger is not from exertion. Freediving can (and should) be done with the absolute minimum amount of muscular involvement. Pulling up an anchor after a scuba dive or even climbing up a ladder with all the gear on is going to be much more strenuous than a good freediver slipping below the surface to a depth of 30 feet and gently floating up.

The issue is with pumping bubbles past the lungs and multiple rapid ascents.

I personally would not be too worried about a few 30 ft dives after a 45 minute surface interval. In fact if the diver ascended slowly, say 60 fpm or so, it would seem to be not much different than a short scuba dive.

However, the advice to avoid freediving after scuba is smart. Blasting up toward the surface with a load of nitrogen in your blood is not smart. There are many well documented cases of freedivers getting the bends from JUST freediving, so it should be obvious that freediving after serious scuba diving is dangerous.

Who knows how dangerous? If the OP wants a good answer.. push it.. do it a bunch.. see what happens....
 
R

redacted

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The danger is not from exertion. Freediving can (and should) be done with the absolute minimum amount of muscular involvement. Pulling up an anchor after a scuba dive or even climbing up a ladder with all the gear on is going to be much more strenuous than a good freediver slipping below the surface to a depth of 30 feet and gently floating up.

The issue is with pumping bubbles past the lungs and multiple rapid ascents.

I personally would not be too worried about a few 30 ft dives after a 45 minute surface interval. In fact if the diver ascended slowly, say 60 fpm or so, it would seem to be not much different than a short scuba dive.

However, the advice to avoid freediving after scuba is smart. Blasting up toward the surface with a load of nitrogen in your blood is not smart. There are many well documented cases of freedivers getting the bends from JUST freediving, so it should be obvious that freediving after serious scuba diving is dangerous.

Who knows how dangerous? If the OP wants a good answer.. push it.. do it a bunch.. see what happens....

I believe the problem is he was doing a subsequent dive (hence the SI). That may take him into the twilight zone.
 

dumpsterDiver

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I believe the problem is he was doing a subsequent dive (hence the SI). That may take him into the twilight zone.


Nope, the tiny bit of nitrogen gained or lost on the SI dives is NOT the issue...

Many times I have freedove hard for hours, doing many dives below 60 feet and then went scuba diving to the no deco limits. I might put a little buffer in my scuba dives and stops, but I'm not too worried. I would not freedive like that after scuba however..
 
R

redacted

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Nope, the tiny bit of nitrogen gained or lost on the SI dives is NOT the issue...

It seems to me that depends on how much your subsequent dive is pushing NDL. Unless you factor it in somehow, like take your computer with you, you may lose track of your NDL status.
 
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