Many divers believe that decompression theory is an exact science. They probably base their opinion on the fact that it includes relatively complex notions such as algorithms, compartments and periods, in short… mathematics. Even current decompression models, which take into account the quantity of gas present in the body in its free form (in particular the VPM and RGBM models), rely on physical laws such as Laplace's law to describe in advanced mathematical terms the behavior of bubbles in the body of divers. Seen like this, it is hardly surprising that the latter see the theory of decompression as an exact science.
While mathematics is certainly an exact science, perhaps the most exact of all, the theory of decompression is nothing other than a simplified mathematical simulation of a complex biological phenomenon, even today. However, the mathematical models used can give exact and certain results, without however a concrete reality conforming to them. To simplify this concept, we could say that decompression biology… does not obey any mathematical model, but does what it pleases!
For this reason, mathematical models are constantly being revised, updated or replaced to more accurately represent this real biological phenomenon. It remains the duty of the diver to stay informed of changes proposed and validated by researchers in the scientific field, otherwise it could put his life in danger!
Let's see what we can learn as a lesson on this subject, following the last annual conference of the EUBS (European Underwater and Baromedical Society), kindly transcribed by Dr Pasquale Longobardi, Medical Director of the Hyperbaric Center of Ravenna, in Italy. We will be presenting the lecture as a true or false quiz, in two parts, so that divers can keep their knowledge up to date without getting bored. Here is the 1st part.
The period series of traditional decompression models (5, 10, 20… minutes) is now well established.
FALSE ! As Dr. J. Kot has indicated, the meta-analysis of decompression models shows that every thirty years or so, a significant change is made to the periods, without the probability of occurrence of decompression sickness significantly changing. . It has also been determined that the maximum period for a diver, even during saturation dives, is between 360 and 420 minutes.
The safety curve - the time limits on the bottom, at different depths, for which no decompression stops are necessary - is basically the same on many dive computers.
TRUE ! This is not a proof of the accuracy of the theory of decompression, but rather a consequence of the alignment of these models on a "safety curve" which has been the subject of experiments and which has turned out to work relatively well.
Even in the current decompression models, which take into account the amount of gas present in the body in its free form, notably the VPM and RGBM models, random mechanisms such as the critical volume algorithm and the critical radius have been incorporated to allow the model to adapt to experimental results.
The decompression measurements reported by several computers during routine dives performed by recreational divers are about the same.
ALMOST TRUE ! There are more 50 models of dive computers on sale now in Europe, but no manufacturer clearly indicates how the computer calculates decompression. In addition, European regulations on the certification of dive computers do not take into account decompression models. Mr. Sayer tested 43 computers during dives performed between 15 and 30 meters with decompression times oscillating between 0 and 30 minutes. In 94,9% of tests, there was a difference of ± 10% in decompression time calculated by computers. In some cases (1%), there was a difference of more than 25% compared to the average time calculated by several computers. For example, for the 15 dive, the safety curve had a maximum difference of no less than 24,3 minutes between the most severe computer and the most "permissive" computer. The most severe computers are as follows, in descending order: Mares Icon HD, Mares using the RGBM algorithm, Uwatec using the Bühlmann algorithm, Suunto using the RGBM algorithm. The least permissive is the Oceanic using the Bühlmann / DSAT algorithm.
A dive computer is enough to handle the short decompression stops that recreational divers can have.
FALSE ! As part of Mr. Sayer's tests mentioned above, on 1 031 working hours, 28 computers required a battery change and 19 presented a screen freeze problem, usually due to the battery. These results clearly show that it is in the interest of each diver to bring at least two computers to check the decompression stops, to compensate for the risk of battery malfunction. It is also important to teach, during dive training, the use of a valid decompression procedure to follow in case of computer failure, even for dives performed in the safety curve.
See you soon for the rest of this article written by Stefano Ruia for Alert Diver the magazine of DAN Europe.
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Well!!!!! when I was talking about level 1 padi I meant open water of course, but I'm fed up with these English words, even though I practice Shakespeare's language a little. Badly worded my humor? don't worry, I have another one on CMAS and this greasy to all of you who have strength to take you seriously have confirmed me in the idea of trying to cheer you up! a man who has no more dreams is an old man before his time. An adult who has no more humor is a boring person! tell yourself one thing people who take themselves seriously there are plenty of cemeteries. It is also only there that we are all equal. I started diving with an N1 a long time ago at club med. When we were celebrating a patent, we drank champagne while standing in circles under the water. It was magical because with the pressure the champagne stayed in the bottle. You could even think that it was an educational tool! in any case we remembered it. Now it is even forbidden to take a bottle on a diving boat —————— but where are we going? ————— more traditions ———— more fun ———————- more user-friendliness ———————–but the race for money and say that there are people dumb enough to accept this. I have even seen cops in Guadeloupe controlling divers underwater. Fortunately they did not control me otherwise I gave them a sign that he could not refuse at 40 and since they had a simple fenzy it was not won. Of course if no ascent I will have lodged a complaint against this gendarme .——————. Obviously I also took the cabbage with the head of the center to whom I still left some 1000 euros. No matter how much I explained to him that I was doing more than 10000 km so as not to be pissed off, I don't think he understood. Tell yourself one thing, freedom is a precious good that must be defended every day. It's not just our sport that is getting really boring. Formerly I was a skydiving MF with the common core of sports educator. With some 600 jumps to my credit. Wanting to reconnect I went to Spain to jump. Do you know what the guy on duty told me? OK we take you and we do a tandem after of course a sloppy instruction. obviously it is profitable it costs about 350 to 400 euros. As I disagreed I said to him “would you please look at my logbook” answer no it's not worth it. If you want to jump classic you first pay 1000 euros and you start all over again. But where are we going? if I am telling you that, it is because sport is now structured to make money all over the place, without taking the value of people, nor taking into account the fact that it is also a hobby. If we have to be pissed off all week and in addition start over the weekend I understand that some have lost all sense of humor.! You want some controversy you will have, although that was not my goal at all. Padi has something else to offer than a big swig of Ricard once on the boat, say Nicolas. Well excuse me for telling you Nicolas but they are living dead !. besides there are some who forgot to live and who died before their time! this poor Cousteau must be turning in his grave. There is only one area where they are alive and well, it's to ask you for your credit card !. I don't want this Anglo-Saxon system. As for criticizing the French for their associative clubs, at least they are often volunteers who use their time and their knowledge, and we are at least sure that they do not do that to grow fat on the backs of poor idiots who are stupid enough to be bamboozled. And yet I am not a club. Besides, it is unfortunately not even more certain that there is a good atmosphere in these clubs. So you have my truth each has its own, and of course I respect that of others as long as it does not take away my freedom.