Hello,
I'm starting to look at decompression diving and I can't seem to wrap my head around some of the theory. I've taken the online DAN classes and I understand that the modern Buhlmann algorithm uses 16 tissue compartments that each have their own half-time for saturation. I get lost when I try to understand how the saturation of each compartment is used to determine deco stops and how gradient factors affect this.
I am getting late into this conversation but ....
I will not repeat the suggestion given about book readings.
I want just to highlight that you correctly say the algorithm uses 16 compartments but these are mathematical abstractions using a dissolved gas (exponential) solution law. Gas enters and exit from one compartment according to time and differential pressure.
If there are 16 compartments, it seems like there must be a system of determining whether it's more important for fast tissues to be off-gassing at a particular speed (determined by pressure ratio?) but on those stops, won't the slowest tissues continue to on-gas? I think I understand what's happening for a single tissue compartment, but not how the different ones interact.
I read somewhere that the Buhlmann algorithm was open source and went looking for the code or mathematical explanation but I either couldn't find it or it went over my head.
Thanks for your help!
But then when you ask how compartment interact between them you give the impression you believe that there is a correspondence between a tissue and one compartment. I.e. blood is compartment 1 with an half time of 5 minutes. This is is believed not to be correct. Think about it. If it is sufficient to take a breath or two of He (no oxygen) to render unconscious a person, probably blood if faster than 5 minutes ...
The ENTIRE ZHL-16 model is representative of the whole body. If you wish to understand relationship between tissues on gassing and off gassing you need to study physiology. Perfusion and diffusion of bodily fluids and mainly blood and lymphatic circulation are the main culprit for interactions between tissues.
Buhlmann, as far as I know (ready to stand corrected), did not postulate interaction between compartments. I am out of my depth here (pun fully intended) maybe more qualified reader (
@Dr Simon Mitchell for example) might come to the rescue.
Now not to open a can of worms but, the debate about deep stop or not deep stops concerns decompression efficiency. I.e. after a given dive, would be better (more efficient) to distribute x number of minutes deeper or shallower? The NEDU study proved that is better to go shallower, but if you feel doing a deep stop and then consider it an extension of dive time rather than decompression time and therefore increase you shallow decompression time you will do more decompression. This would off gas the additional inert you have on gassed staying deep longer, you might have reduced the gradient on you fast tissues early on, and compensated for the need of off gassing longer the slower tissues after the further on gassing imposed by the early stop. Obviously it would have increased the total deco time and decreased decompression efficiency. We recreational diver enjoy being in the water and a few minutes more do not matter, but people doing it for work, in difficult conditions (sea state, temperature), costing money, want out of the water safely as fast as possible, after the working phase of the dive is over.
Finally and once again the use of tissue and compartment is not interchangeable, this was my key message.
Hope this helps and not confuse.
Critical reading of the available material might prove helpful (meaning weighting source and reference not only number of posts
). Some vocal supporters of the deep stop theory, loudly advocating against scientific evidence, lost their posting privileges here thus reducing the background noise.