Dear Readers:
Phase Transitions
Depending on what you want to know, I can offer a few words of a qualitative nature. If you already knew this, then I am sorry that I did not contribute much. Here goes.
In the Haldane model of decompression sickness, inert gas was always in the dissolved state. If the metastable limit were reached, bubbles would form. This limit was a concept taken (apparently) from the physical chemistry of the day that indicated that supersaturated solutions could exist for long periods of time. If the supersaturations were mild, very long times without two phases forming (e.g., solution and bubbles or solutions and crystals).
This question was studied because fractional crystallization was a method employed to purify and separated slats in industrial settings. The problem with this was that extraneous crystals or dust motes would upset the balance and allow crystal formation when it was unwanted. In the case of solutions of gases, small microbubbles could cause frank bubble formation.
Haldane Method
The problem with the Haldane theory is that it is known that fluids contain microbubbles. They are virtually impossible to remove from a fluid. Fluids that are in motion contain more nuclei than those that are at rest. This is an idea that dates back to Edmund Newton Harvey in the 1940s. The concept is referred to as stress-assisted nucleation.
RGBM
The models of Yount and Wienke incorporate bubble nuclei without specifying their origin. It is not really necessary to know where the nuclei arise or by what method. The problem is that they control decompression bubble formation. The link between the Haldane model and the gas micronuclei model is the equation relating surface tension and bubble radii (the Laplace equation). Because of surface tension, small bubbles are difficult to grow unless the supersaturation is large.
One arrives are large supersaturations during the initial ascent to the first stop in the Haldane scheme. You then carry these bubbles along throughout the decompression and the decompression becomes very long. This is sometimes referred to as bend and mend tables. Reducing the magnitude of the first stop will prevent the growth of these micronuclei. Deep stops are the way to do this; hydrostatic compression is another. The fist is possible but the second is not (with air breathing creatures).
Deep Stops
Deep stops are incorporated into certain tables. The stop depths and times have been calculated from analysis of diving data and determing the dive outcome. With deeper stops, divers report successful decompression with less decompression time (an idea of Brian Hills in 1986). In addition, divers report a subjective feeling of being less lethargic.
There is little doubt that the tables work. What is unclear is, do they work for the reasons given? In the absence of a laboratory study, it is difficult to say.
Dr Deco :doctor:
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