One can credit any number of things for this reduction in injury rates (my emphasis): better training, improved standard equipment, better planning techniques and smarter choices in mixes and gas swaps, and better deco models and planning tools, and increased use of wrist computers.
Ross,
First, I would congratulate you on a much more balanced paragraph on this issue than you have produced in the past (when you have been enthusiastic about attributing your perceived improvement in safety almost solely to the use of bubble models).
Unfortunately, you continue to perpetrate an unsubstantiated claim that the rate of decompression sickness (DCS) in technical decompression diving has declined. To calculate a
"rate" you need a
numerator (number of DCS cases in technical decompression dives) and a
denominator (number of technical decompression divers or dives). You actually have neither. All you (sort of) have is an imprecise and tangentially relevant numerator (number of DCS cases in ALL recreational diving).
It is true that the number of DCS cases in all recreational diving has been reported as falling by a number of authorities. An example is our own data:
see this post. However, this tells you very little about what is going on in technical diving. In terms of numbers, technical decompression diving is a tiny subset of the all recreational diving and it would be possible (and indeed plausible) for DCS numbers in all recreational diving to be falling whilst numbers in technical decompression diving are actually rising. Put another way, you cannot look at the numbers of DCS cases for all recreational diving and simply assume that the same trends hold in technical decompression diving. Put yet another way, you don't even have an accurate numerator, let alone a denominator.
Then there is the issue of what those numbers actually mean (and that is where the denominator becomes important). For example, the fall in DCS cases in all recreational diving may be nothing to do with safety improvements and simply about numbers of participants. Again, see
this post for a
real published data example of how this appears to be at least part of the explanation in our jurisdiction. I am not suggesting that numbers of technical divers are decreasing, but this is a great example of how easy it is to make errors in attributing causation for an apparent trend without having all the facts.
One of those other relevant facts, that came into play at virtually exactly the same time as VPM appeared, was an international agreement that milder cases of DCS could be managed adequately without recompression. There are no accurate data describing exactly how this impacted on recompression treatment numbers globally, but based on discussion at diving medical meetings it is likely to be substantial. This is yet another example of a way in which attribution of causation for lower DCS treatment numbers can be confounded.
Finally, as I have told you in the past, based on experience of acting in the role of medical officer for over 10 major technical diving expeditions to remote locations, I believe there is a substantial burden of unreported relatively mild DCS among technical divers that is self treated in the field. It follows that even if we had a numerator for DCS cases in technical decompression dives, there would be problems with accuracy.
The issue of trends in decompression safety is one of fundamental importance to the sphere of my professional interest. It follows that every time you misrepresent that issue on diver educational forums I will point out the flaws in your argument. That paints you in an unfavourable light and is time consuming for me. So why don't you just stop doing it??
Simon M