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Yes, it is trivial. But it really is the point of debate it seems ;)

Sigh. I left out "net", for simplicity. Yes, a lead brick will generate buoyancy, but this will be smaller than the antiparallel vector of gravity that inevitably results from the mutual attraction of the Earth and the lead brick. It will thus sink. A water brick will generate buoyancy in water...

boulderjohn, "zero buoyancy" means no force antiparallel to gravity because of displacement of surrounding medium. I do not take objection to your statements regarding an imploding or flooding scooter loosing buoyancy and thus becoming negative. That is completely correct! The only thing that...

Any volume only generates buoyancy when it is filled with something lighter than the surrounding medium that is displaced. When the cylinder is flooded, the light stuff (air) is lost and replaced by the same type of matter that is displaced (water). The buoyancy of the volume that is flooded...

boulderjohn, as I have written twice, something completely flooded can not implode, as it is for practical purposes incompressible. No disagreement there. The thing is that you arrive at the right conclusion (implosion leading to massive loss of buoyancy) via a misunderstanding. In terms of...

Under water the same as if completely flooded. We sorted this out already. Something that is already completely flooded can not implode at depths reachable to a human.

If a completely flooded scooter somehow managed to implode actually not. A water filled volume is neutral in water. The only thing that will in theory change is the drag when the scooter gets compressed. Probably not a huge factor. In reality incomplete flooding is however a necessary...

The problem here is that nothing is known about the accident. It is therefore not at all good reasoning to extend "most accidents could have been avoided by following basic safety procedures" to "this specific accident could have been avoided".

Well the "no different dimension" requirement probably rules out diphenhydramine then...

With relevance to arterialisation of bubbles, I would think various forms of shunts in the heart and the lung, yes. With regard to testing, all tests involve injecting bubbles, so there is a small risk. And a TCD will not show the exact location of the heart shunt, so if you want it closed you...

The first part is certainly true, a PFO can shunt bubbles. But it is far from the only shunt a human can have. The shunted fraction is very small, so anyhow the "target" tissues would still have to be prone to bubbling. And in the end, what matters is not appealing theories of how causal chains...

Michael, care to elaborate on scientific sources for this drastic view? If it is of help, there are I think some of the real experts in the medical diving community following this website. One can find their postings in the board. I understand the consensus view is to not advise testing for a...

mac64, I think this is really not correct. Saturation and desaturation are driven by the gradient, not by the amount of gas available. The only thing that breathing rate can theoretically be relevant for is as an indirect measure of exertion, and thereby probably perfusion. More perfusion will...

The Chairman, to that I wholeheartedly agree!

OK, I mis-read then, sorry for this. However, 6 minutes versus 2 minutes is mathematically a factor three, sure. But the difference of 4 minutes may easily be within any margin of error in any model, no?

I do not read out of his postings that John did 3 times the deco his plan would have mandated? I thought the "three times" part of the comment was in response to the Chatterton quote, to say that there is an amount that is surely enough, but there is also a grey area? Anyhow, as said, he also...

"If it were me, I would be checking myself for a PFO, and if that was negative, I would never go into deco again." Isn't this vastly overestimating the role that PFOs may or may not play? It is not like they are the one outstanding cause above all others... Also, he posted that he had himself...

" I worry that this is simply a statistical issue and that, if I dive enough, someday, the factors will simply align and I will have a DCS hit." I actually think this is true, and something very important to consider...

If I am allowed to say, I am not really convinced that any conclusions can be drawn yet. Without the slightest indication what actually happened, to me it is not at all clear if the scenario would have played out with a better outcome had a buddy been there, or any given type of gear available.

I would however be more careful. The situation is that we have something that is very common (PFO) that people think may be correlated to something that is very rare (DCS). And there is an exceedingly sexy explanation that may link both things (arterialisation of venous bubbles). From the...