Here's a "heads up" to Heads Up,...it truly is NOT a simple subject, but there ARE ways to simplify the application of it!
To break it down somewhat, it is good to look at it from a basic perspective.
The deco programs in use are (1) Haldane-based (or neo-Haldanian, as Charlie pointed out), and (2) non-Haldanian.
Most of the popular, (here read prevalent), programs are directly based on Haldane's work, with added modifications, or "tweaks", and thus can be labled "Neo-Haldanian". As such, they deal with gas as it moves into and out of solution.
A real argument begins when you get to the non-Haldanian category. It could be argued that any time you deal with gas in solution in the body, you are dealing with a subject researched and more or less "codified" by Haldane. Therefore, in the strictest terms, all of the newer work is at least neo-Haldanian. Now, of course, it can and will be argued by the mathematicians and physicists that the mathematical model is completely different, and therefore the previous statement is not correct. I would have to venture that this would be a subject for them to argue. For the rest of us, it does not matter a heck of a lot!
What does matter to us is ease of use, and the general level of safety in the practical application, i.e. our diving. We as divers must recognize that NOT ONE of these programs can offer a 100% guarantee of safety. If nothing else, that is not statistically possible.
It then behooves us to find a model that has been well researched, both mathematically, and physically.
A good example is the Reduced Gradient Bubble Model (RGBM), created by Dr. Bruce Wienke, of Los Alamos National Laboratory (LANL). RGBM is a deco model that treats both gas in solution, and gas in the free or bubble phase.
Dr. Wienke is, in actual fact, a nuclear physicist. He is also a diver, and an advisor to various government special operations dive units.
Dr. Wienke has put his model through rigorous mathematical testing, using the super-computers available to him at LANL. (I would venture to say LANL has at least as much computing power available as the NSA (No Such Agency), and perhaps more so.
The model has also been rigorously tested by human "crash test dummy volunteers" from various government dive groups, Tim O'Leary's NAUI tech research folks, IANTD's Tom Mount, and others, and has proved to be extremely successful.
It has been suggested to me, by certain individuals in the profession who should know, that the latest iteration of the "GAP" by Kees Hofwegen, is the best example of a full-implementation RGBM program currently available. I do know that the "GAP" has a good user interface, and seems to be relatively intuitive to use. It also offers a fair amount of user adjustable factors to account for such things as workload, temperature, and user preference (i.e. diver desired level of "conservatism").
For an excellent treatment of the subject of decompression and of the RGBM, I would recommend the book "Technical Diving in Depth" by B. R. Wienke, offered by Best Publishing. I would be the first one to admit that I am not a mathematician, either by trade or preference. There is, however, enough explanation in the text to enable one to "read around" the math and understand what has been done with the concept. For those so trained and inclined, Dr. Wienke has included the math as "proof of concept".
I hope that this will be helpful to you in your understanding of a sometimes nebulous and often confusing subject!
BJD
