Science behind GF

[Rooster59]

You might want to look into linear-exponential model (VVAL18) by Thalmann. Thalmann algorithm - Wikipedia
There's the assumption that bubbles slow down off-gassing, with the effect that a higher gradient does not increase off-gassing rate. That's the opposite of your concern: you assume that GF100 will have a much higher off-gassing rate than GF50, making GF50 less safe than assumed, whereas in the VVAL18 model assumption, bubbles make GF50 off-gassing stronger than assumed and almost the same as GF100.

So I have a question, is the assumption that bubbles slow down off-gassing the underlying idea behind doing a safety stop for non-deco sport diving? Similar but not the same as reducing the GF?

 

[ChuckP]

Does this help?

Light bulbs going off everywhere, I hope that article is as close to correct as need be cause that's about the simplest terms I've ever seen it explained in.

 

[J-Vo]

So I have a question, is the assumption that bubbles slow down off-gassing the underlying idea behind doing a safety stop for non-deco sport diving? Similar but not the same as reducing the GF?

I believe the safety stop is primary to slow unskilled divers down because they tend to ascend to fast. Even if you ascend properly, allowing more off gassing before surfacing is never a bad idea.

 

[Magnus Lundstedt]

The other things to remember:

Deco theory is just that - theory

Nothing is "Just a theory" A theory is the highest level in scientific explanation.

 

[sea_ledford]

Nothing is "Just a theory" A theory is the highest level in scientific explanation.

Well, yes and no. In this case we aren't talking about the Theory of Decompression as if it were equivalent to the Theory of Evolution. We are talking about how decompression works theoretically, based on mathematical models that may or may not mimic biological tissues accurately.

And the highest level in scientific explanation is a Law.

-Chris

 

[atdotde]

I think the assumption that the rate of change of pressure is proportional to the difference in pressure between the tissue and the environment is pretty reasonable (the keyword being diffusion): As the pressures are proportional to the amount (say: number of molecules) of gas, this assumption simply says that each individual molecule is equally likely to cross the barrier between "inside" and "outside", no matter if it is inside or outside. It essentially does a random walk. Just as there are more molecules inside (or better: their density is higher) the rate (as in number of molecules per second) outwards crossing is higher than that of the opposite direction.

You would only get a different rate if you dropped this "essentially random walk" assumption (which not even the bubble models do, there the criterion is more complicated than an m-value but this gas loading/unloading mechanics is the same).

 

[rongoodman]

And the highest level in scientific explanation is a Law.

Not correct. A scientific law, such as Newton's Law of Gravitation or Coulomb's Law, simply summarizes repeated observations. It makes no attempt at explanation.

 

[lermontov]

Nothing is "Just a theory" A theory is the highest level in scientific explanation.

Well, yes and no. In this case we aren't talking about the Theory of Decompression as if it were equivalent to the Theory of Evolution. We are talking about how decompression works theoretically, based on mathematical models that may or may not mimic biological tissues accurately.

And the highest level in scientific explanation is a Law.

-Chris

Not correct. A scientific law, such as Newton's Law of Gravitation or Coulomb's Law, simply summarizes repeated observations. It makes no attempt at explanation.

you guys need a hobby

 

[BenjaminF]

you guys need a hobby

Being physicists or pendants isn't a hobby??

 

[leadduck]

I think the assumption that the rate of change of pressure is proportional to the difference in pressure between the tissue and the environment is pretty reasonable (the keyword being diffusion): As the pressures are proportional to the amount (say: number of molecules) of gas, this assumption simply says that each individual molecule is equally likely to cross the barrier between "inside" and "outside", no matter if it is inside or outside. It essentially does a random walk. Just as there are more molecules inside (or better: their density is higher) the rate (as in number of molecules per second) outwards crossing is higher than that of the opposite direction.

You would only get a different rate if you dropped this "essentially random walk" assumption (which not even the bubble models do, there the criterion is more complicated than an m-value but this gas loading/unloading mechanics is the same).

Correct for VPM, but in VVAL18 there is a different idea: In a supersaturated tissue, there's more gas than what can stay dissolved, and this extra gas forms bubbles. Only the dissolved gas in the tissue participates in diffusion, whereas the gas stored in bubbles does not, so that the diffusion rate has a maximum for saturation and does not grow further by supersaturation. This constant diffusion rate is the reason why supersaturated tissues off-gas linearly and others exponentially --> LEM.
VVAL18 however wouldn't be called a bubble model because it doesn't model bubble growth like VPM; it just tracks the amount of dissolved gas and gas in bubbles, so it's a two-phase model but not a bubble model.