OK. Let`s say the dive is done in the same way, with the stops before surfacing. Isn`t the methods pretty much the same?
Yes, of course they are. Nobody diputes that. The problem is the cost, the availability, the logistic, and also importantly the time. You can do the O2 deco prettty instantly after the SP, or even before it (in training or in emergency). And in training you can stop for the O2 deco already during the ascent. When using a portable deco chamber, the entire process of extracting the potentially uncoscious or convulsing diver, putting him into the chamber, and recompressing - it would take surely at least 5 minutes, perhaps much more. And each second may be very important in this case, so it makes a huge difference. Additionally you would have no way to perform CPR if needed. Still, of course, you are right that if there were no complications, the chamber would allow for better and more controlled decompression. And even in the case of an inconscious diver it may still offer better choice than the submersion. That's not the question. The principal is chosing such strategy that minimizes the need of a long and a deep deco. But I think you are rigtht that for such extreme dives, having a portable deco chamber on the boat would be wiser anyway.
And this one I don`t understand: How is that possible? The dives on air I described would not be treatable with breathing O2 for 20 min. If you can be treated in 20 minutes you don`t really have a big saturation do you?
As I said, my knowledge with DCS is from normal diving but the thing I do know is that there is one good thing about bubbles: You can make them smaller by increasing the pressure
Yes, of course, you can make bubbles smaller by compressing them, but that's why I wrote you cannot compare scuba deco with freediving deco, and you may need to compress a freediver more than a scuba diver saturated to the same level, because due to the cerebral vasodilation, at the freediver the vaste majority of bubbles will form in the brain, will form bigger, and deeper in the capilaries, and will be ten entrapped with the vasoconstriction after surfacing, so will resist more the compression.
Another factor not yet well studied or understood, is the contribution of CO2 at freediving DCS - it may play a more important role than N2. CO2 gets quickly dissolved, metabolized, and removed from the blood when ventilating, so the biggest risk of the CO2 is not after the dive, but during the ascent, when the bubbles may cause a lot of damage. For this reason the slow ascent, and deco-stops during the ascent at extrem dives like this, are important, and why the post-dive deco is less important / less helpful than at scuba.
So again, the choice of the strategy reducing the need for the deco is crutial. The post-dive bend-and-mend deco is not the solution, regardless how good it is. From this point of view, the FRC approach as used by Seb Murat and described in another thread may be the way to go. I was shocked seing Herbert telling already a few days after his accident that he was going to continue to 900 and 1000 feet, despite the accident. If he does not completely change the way he dives, I see no way how he could survive a deeper dive than he did.
