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Sebastien Murat interview

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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Conventional wisdom has it that the human dive response is not strong enough to enable people to perform underwater on no air. At the same time, it is full lungs, not empty ones, that make freediving so dangerous.
Back in his hut, Murat plots on his laptop the data stored on my monitor. The graphs please him. "Going down on empty lungs your heart rate was lower and recovered much more rapidly, which means that you can go down more frequently, more safely," explains Murat. "Chances are you can also spear more fish."

This was printed in a mainstream newspaper. It wories me a bit as it seems to imply that diving on empty lungs is safer then diving on full lungs ??

In my opinion empty lung diving is probably the most dangerous thing you can do. It's the easiest way to black out as often the CO2 doesn't build up any quicker and your O2 runs much quicker. You also sink and do not float up so is also harder for the safety diver. My worst ever blackout was doing an empty lungs warmup. It may work for Seb but for %99 of all freedivers, diving on empty lungs will greatly reduce both their time and depth.

I'm sure Seb didn't imply that but you have to be really careful what you say to the media as they just like printing something thats sounds exciting rather then sticking to facts.

i think you raise a very important point here Wal...

i worry about the monkey-see-monkey-do factor here. we as freedivers know that empty/FRC diving is serious stuff and you *really* need to know what you're doing. i'm sure a lot of beginner freedivers/snorkellers will be intruiged by the article and may be tempted to try it out for themselves... without appreciating the risks involved.
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If you read the article there are certainly quite different views about what is safer empty lung diving or full lung diving.

The no limits attempt however was done with full lungs and much packing. This could mean that at the moment even for top freedivers there seems to be a limit on how deep they go on empty lungs and when they switch to full lungs.

Very interesting to see that there are very different approaches to freediving, even on the subject of how much or how little air you want in your lungs. And Sebastien Murat shows that both methods can be used to reach great depths.
Does anyone know why freedivers seem to stick to a maximum descent rate of about 2 meters per second during the WHOLE dive?

What are the limitations that dictate the often constant descent speed?

I would guess that at great depths a higher speed could be possible because pressure changes become relatively smaller very quick as one gets deeper. For example:
0-10 meters depth gives a pressure change of 100% (1 atmosphere to 2 atmosphere)
10-20 meters depth gives a pressure change of 50% (2 atmosphere to 3 atmosphere)
40-50 meters depth gives a pressure change of 20% (5 atmosphere to 6 atmosphere)
90-100 meters depth gives a pressure change of 10% (10 atmosphere to 11 atmosphere)
190-200 meters depth (murats wish) gives a pressure change of 5% (20 atmosphere to 21 atmosphere)
When deciding descent speed, there are two main factors:
1. Equalizing
2. Blood shift

The speed at any time must be slow enough to allow for both equalizing and blood shift. In the beginning of the dive, the pressure change is the most, so equalizing is an issue, but recent discoveries point to the idea that if packing, a slow initial descent is necessary to allow for blood to return to the lungs (after being pushed out from packing).

Then, in the extreme deep phase, perhaps a slower speed may be needed as the alveoli start to swell up....

Eric Fattah
BC, Canada
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