Your posts seem to have conceded that the research shows that bubble-model-style deep stops increase the risk of DCS.
Actually, I think we need to be careful to be accurate about this statement. The NEDU study studied different ascent strategies in order to compare the
relative efficiency of the ascent strategies calculated by the models.
After having read and followed a great number of these threads, I personally think that a number of conclusions can be drawn from what they discovered. I should qualify this by saying that I am not a decompression scientist, just a diver. However, the conclusions I read from the research are:
- Ascent strategies including deep stops are less
efficient than Buhlmann-style ascents that get the diver shallower faster.
- Ascent strategies including deep stops do actually protect fast tissues as they claim, but at the cost of increased tissue loading in slower tissues.
- On sufficiently extreme dives, the fast tissues are not the ones implicated in the formation of DCS, so it would appear that the deep stop algorithms are working with some incorrect assumptions.
As it stands right now, I think it's safe to conclude that on sufficiently extreme dives, that existing bubble models are not calibrated well enough to protect the diver from DCS as well as the Buhlmann algorithm. On sufficiently extreme dives the existing bubble models would appear to need "padding" on shallow stops and will probably result in longer decompression times for similar profiles than one would need when using a Buhlmann model.
The issue for divers is :
a) we don't know how much padding is enough because the algorithm doesn't help us calculate that
and
b) when given a choice between a
more efficient and a
less efficient ascent strategy, it would seem illogical to choose the less efficient variant.
and
c) a very pertinent issue for scuba divers is that their ascents are very seldom as perfect as the ascents tested in the lab. Therefore the model must be able to adjust to deviations in the intended ascent plan in order to advise divers accurately about the required shallow time.
Having said all of that, however, what I can NOT conclude from my reading of the NEDU study is that deep stops in and of themselves are somehow dangerous and/or lead to a higher risk of DCS. What I DO conclude from the study is that IF you do deep stops, you need to compensate for that with more time shallow. A Buhlmann based computer will calculate that for you, a bubble model such as RGBM/VPM/BVM (the model NEDU used)/Ratio deco et.al, won't do so accurately enough at this time.
So let me say that again. Deep stops are fine
IF you aware that they don't have any particular benefit beyond protecting fast tissues
AND are using an algorithm that will calculate the necessary padding well enough. My reading is that Buhlmann algorithms appear to do that better than bubble algorithms.
Finally, there is the issue of calibration. I'm not 100% convinced that ANY algorithm is perfectly calibrated. Extreme deep divers all use Buhlmann but none of them use it the way a "garden variety" technical diver like myself would. To the best of my knowledge they all pad the shallow stops a lot more than Buhlmann calculates because there appears to be drift in that algorithm as well. In other words, no algorithm is perfect. To my way of seeing, Buhlmann is currently the "least imperfect" algorithm we have at this point in time. Perhaps in the future scientists will find a way to calibrate the bubble models better and in a few years we'll all be tearing down Buhlmann online instead.
R..
