what is "altitude diving" and max # of dives

[M_Bipartitus]

I hear what you're saying and I'm not going to say you're wrong but intuitively... the harder you blow.... (at least before boyle's law takes over) the more air you can push through a sheet of silk.

I personally have my reservations about the things Dr. Wienke says because (a) I suspect his motives are to make profit and not to be "right" and (b) his theory only seems to hold for a narrow bandwidth of dives. At extreme depths all the masters of our sport are still using Haldane. There's a reason for that.

I'd like to have Dr. Powell's opinion on this before we go further.

With your permission I'd like to have this thread split and the last bit kicked into the Dr. Deco forum. I think it's important for us to have an expert opinion on this.

R..

I'm not sure how much you know about the differences between these models for decompression and the reasons that Dr. Wienke came up with the RGBM. The Haldane model only assumes that individual compartments saturate and empty assuming a simple exponential increase and decay. the RGBM takes into account data that suggests that gasses can diffuse out of a tissue at a slower rate than they enter. This is reasonable based on the formation of small, non-symptomatic, bubbles in the body, which trap air and slow it's release from the tissue.


Also I suspect profit is not that high on Dr. Wienke's motives as his day job is a scientist and a national lab. I will admit I didn't have time to meek him when I worked up there, but I can tell you from what I know LANL scientists do pretty well without outside income.

 

[AzAtty]

I have no objection to splitting the thread to get Dr. Powell's comments. I always value his commentary.

Maybe the better analogy is this: a sponge absorbs water at the same rate, regardless of its position in the water column.

 

[Diver0001]

Also I suspect profit is not that high on Dr. Wienke's motives .

Fair enough. I personally think Dr. Wienke wants to get rich on his "intelllectual property...." and doesn't give a rats ass what happens to the divers who test his "theory" in the field.

I have no idea which of us is right-- except I know that there have been divers bent using Wienke's algorithm and he has blamed the computer programmers for the errors (which were not made by the programmers) instead of taking responsibility himself.... To my way of thinking, he shows the behaviour of someone wanting to have his cake and eat it too...

YYMV, but I don't trust him.

R..

AzAtty, I'll ask another mod to take a look at this and consider splitting it. I'm obviously involved in the thread and I don't want to moderate a thread I'm involved in.

R..

 

[knotical]

Even if halftimes are independent of pressure, that's not the same as saying that on- (or off-) gassing rate is independent of pressure. Half-time is a measure of how close a compartment has come to saturation at a particular pressure. If we go to a greater pressure, with the half-time being the same, it will take more molecules of gas to reach half-saturation at the greater pressure. So going directly to two different pressures would result in two different rates of on-gassing.

 

[segraves1]

haha, I started a good covorsation.....

While I agree that there is an issue of tissue having a specific rate of obsorbition (call it a coefficient of obsorbtion...), this "coefficient" must be affected by pressure differential, though probubly not a linear function.

 

[AzAtty]

Even if halftimes are independent of pressure, that's not the same as saying that on- (or off-) gassing rate is independent of pressure. Half-time is a measure of how close a compartment has come to saturation at a particular pressure. If we go to a greater pressure, with the half-time being the same, it will take more molecules of gas to reach half-saturation at the greater pressure. So going directly to two different pressures would result in two different rates of on-gassing.

Perhaps we should clarify. What I'm getting at is the physical properties of the tissue don't change based upon pressure. When I say "rate" I mean that the logarithmic function that describes inert gas absorption does not change based upon pressure. Neither perfusion nor diffusion coefficients include pressure as a variable. Instead, those coefficients are dependent upon a tissue constant that is a function of a tissue half time.

Now, the instantaneous rate of tissue tension change is dependent upon initial tension and ambient pressure, but how "fast" a tissue absorbs inert gas is still constrained by the perfusion and diffusion coefficients and gas solubility.

 

[M_Bipartitus]

Each component in a decompression (they include a number of components) model has a half-time associated with it and a saturation level. Consider a single component that has a half-time of 30 minutes. This means that it takes 30 minutes to go from the ambient partial pressure of nitrogen to the saturation partial pressure in that component. After an additional 30 minutes the partial pressure in the component will get half way closer to saturation again.

The formal mathematical way of expressing this is a differential equation where the change in partial pressure in a component (rate of gas exchange) is equal to the half-life for the component times the difference between the saturation level and ambient pressure levels. In basic decompression theories the half-life is assumed constant for each component, with newer models there are conditions that allow this number to change.

 

[PToone]

I dive at 6000 ft and do multi dives. I just stay within the altitude tables and I've never had a problem. Dove three dives a few days ago at 6000+ ft.