". . .As I have pointed out before, it is difficult to recommend a definitive practical application of this conclusion to divers for all sorts of reasons. However, the use of GFs does give the diver an opportunity to "de-emphasise" deep stops to an extent. In my own experience, this means that whereas I might have used a GF-Lo of 10 or 20 at the height of the belief in deep stops, I would now use 40 or 50.
Given I am frequently the only diving physician in remote locations I usually also dive a conservative GF-Hi (70 - 75) but that is a personal choice. There is nothing definitive in these recommendations. It just seems like a sensible response to the data that we have as of February 2014. . ."
Simon M
Deep Stops (rebreather dive charts) - Page 22
". . .This brings us to the fact that we have seen the recent emergence of data that suggest the deep stop approach might not be the best one. In particular, these data suggest that the logic of protecting fast tissues from supersaturation early in the ascent at the expense of increased supersaturation in slow tissues later in the ascent may be flawed. Whether one likes the relevant studies or not, they are all we have at the present time to illuminate this issue.
So, was the bubble model fashion a bad idea, and where does this leave the majority who have been using some degree of "deep stopping" with apparently good outcomes? Do we abandon deep stops entirely eg go to 90/90 as you hypothesised, do nothing, or do something in between?
I guess the first thing to acknowledge is that the studies indicating a disadvantage for deep stops are not the diving equivalent of multiple large multicentre randomized trials all showing that the risks of a widely used drug are greater than its benefits. On the basis of that sort of data you would probably stop using the drug overnight. The diving world data concerning deep stops are not as definitive as that. As more data emerge the situation may become clearer (or more blurred)!
So, at the present time, as an informed commentator, I would not go so far as to recommend that the entire world dives 90/90 or 80/80 from tomorrow onward even though I personally would not be surprised if the outcomes were as good as (or better than) what we are getting now (if we were able to measure them!). Partly, this hesitancy to advocate substantial wholesale change arises from the certainty that every diver who subsequently got bent would inevitably blame it on the change in their decompression practice!
The deep stop trend evolved over a substantial period, and if the data continue to be supportive, it may have to "de-evolve" over a substantial period.
Equally, I do believe the data are strong enough (and bear in mind they are the only data) to consider a change in practice if you are a strong "emphasizer" of deep stops. In practical terms, "de-emphasizing" deep stops (or lessening any potential disadvantage) would mean using bubble models on very high conservatism settings, and with gradient factors, avoiding very low GF-lo values.
I have been evolving my own use of GFs and am currently around 50/80 . . .sometimes as low as 70 for the high value when we are at places like Bikini and I am the only diving physician. Pre-NEDU study I was GF lo of 20. This is my personal perception of a sensible graduated response to the way the evidence is currently evolving. I may well go further in future (guided by the evidence).
Sorry about the long post. Hope it makes sense."
Simon M
Deep stops debate (split from ascent rate thread) - Page 13
