Slow tissue on gas from stops

[ajduplessis]

That's generally true, but not what is being discussed.

The question is whether, for identical dives and identical time to surface, the stops recommended by bubble models or the stops recommended by a shallower-stop model (e.g. GF) are more efficient (i.e. result in a lower DCS rate).

The current evidence suggests that getting away from the deep stops recommended by common models like VPM, RGBM, RD will result in lower DCS risk. By how much the risk is reduced, and exactly where the dividing lines are between shallow enough and too shallow, is not known. What does seem clear is that the "protecting the fast tissues" obsession was way overblown and counterproductive to safety.

Not knowing, and I quote “By how much the risk is reduced, and exactly where the dividing lines are between shallow enough and too shallow, is not known” does not sound like science to me.

as I mentioned before, a dive profile with a 20min deep stop with the same identical time to surface to shallower profile will produce DCS higher risk. This was clear to me after OW training....

 

[joe10540]

Didn’t the NEDU study exaggerate the stops to a point where it was almost a reverse GF like 90/30? I am by no means an expert but that theory kinda makes sense to get shallow quick and then surface with less supersaturation. I didn’t actually read the study but watched a video about it narrated by Dr Doolette I think. Very educational video but very hard to stay focused.

 

[UWSojourner]

Not knowing, and I quote “By how much the risk is reduced, and exactly where the dividing lines are between shallow enough and too shallow, is not known” does not sound like science to me.

Being honest about what you don't know sounds like science to me. Current research all points to bubble-model-style deep stops being too deep, and counterproductive. Exactly how best to deemphasize them is still an open question as far as I know.

 

[ajduplessis]

Being honest about what you dont know while emphasizing that current working models are counterproductive sounds like guesswork to me, not science.

 

[Storker]

Being honest about what you dont know while emphasizing that current working models are counterproductive sounds like guesswork to me, not science.

"We have fairly hard data showing that extreme A is counterproductive. We do not, however, yet know exactly how close to B the optimum is, but right now it seems as if somewhere reasonably close to B is fairly right" is definitely science. No matter what it might sound like to you.

It's being honest about what you don't know, and at the same time giving the best recommendation that the data can give us. It's science. And science is all about being dead honest about what the data can reliably tell us.

 

[Dr Simon Mitchell]

Being honest about what you dont know while emphasizing that current working models are counterproductive sounds like guesswork to me, not science.

We now have multiple studies suggesting that the particular "current working models" you are referring to are prescribing stops that are too deep for optimal efficiency, and no studies that suggest different. The studies are published in scientific journals or publications of scientific establishments. Where is the guesswork in that?

Simon M

 

[Dr Simon Mitchell]

Didn’t the NEDU study exaggerate the stops to a point where it was almost a reverse GF like 90/30? I am by no means an expert but that theory kinda makes sense to get shallow quick and then surface with less supersaturation. I didn’t actually read the study but watched a video about it narrated by Dr Doolette I think. Very educational video but very hard to stay focused.

Hello Joe, there is a fantastic explanation of the methodologic choices in the NEDU study here.

Definitely worth a read if you are interested.

Simon M

 

[ajduplessis]

We now have multiple studies suggesting that the particular "current working models" you are referring to are prescribing stops that are too deep for optimal efficiency, and no studies that suggest different. The studies are published in scientific journals or publications of scientific establishments. Where is the guesswork in that?

Simon M

So with all these studies being done, what is the optimal profile? a recommended GF factor with some honesty as not everything is know or clearly understood? All these studies are published yet none of them gives a optimal profile, only recommendations/suggestions. To me this is guesswork.

ajduplessis

 

[Storker]

Hello Joe, there is a fantastic explanation of the methodologic choices in the NEDU study here.

That text isn't only a great explanation of those specific methodological choices. It's also a great illustration of how one should design an experiment to get reliable data and unambiguous conclusions. It should be required reading in any Experimental Design 101 class.

 

[Storker]

So with all these studies being done, what is the optimal profile?

For a proper scientist it goes against all instincts - and is seen as unethical - to give specific recommendations when the data can't substantiate them.

The answer to your question is "we don't know what the optimal profile is, but we are as certain as we can be right now that it definitely isn't a deep stop profile like those prescribed by bubble models." ("we" being a rhetorical "we", I'm definitely not included in that "we"). Simon has divulged which gradient factors he personally uses, but don't ever expect a trained scientist to give you the answer you're asking for as long as nobody knows exactly what the answer is.