100days-a-year
Contributor
Interesting,I may start diving Mix on my EDGE to try this out.What could happen,HE is our friend right?
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Some agencies have taught (and still teach) that when you dive with helium, your deco times will be longer because helium is absorbed into tissues so much faster than nitrogen. Yes, it leaves faster as well, but off-gassing is supposedly not as fast as on-gassing.
In a nutshell
1 - You might need the longer deco that the 'helium penalty' gives you (maybe even more), but not because of the helium, but because longer and deeper dives (where you're apt to use helium) carry a higher % of DCS risk.
2 - For a given gradient factor setting, decompression profiles are not iso-risk across depth and time combinations.
3 - Common deco algorithms aren't great on very long and/or very deep dives.
I wonder whether anyone will adapt the Bühlmann algorithm for Trimix diving?
Adjusting the slope via the a/b coefficients should do the trick, should it not?
Hmmm. Here is some thoughts on those ideas.
1/ If helium is no longer the culprit causing DCS, then what is causing us the DCS that is to be avoided ??? Are they now suggesting that DCS is no longer caused by excessive gas pressure stresses, but instead now its being caused by other (external) influences like cold, or physical activity stresses, or what?? Are they suggestion He now has non-linear kinetic rates with pressure changes?
When we pressed Simon and David on this issue, they respectfully declined to answer, or clarify this conundrum.
2/ Problem with GF in this situation, is that it's over riding the ZHL model. So you cannot be comparing random x/y GF values here. You need to go back to raw ZHL as a comparison point. Also see next answer re; iso-risk.
3/ ZHL has issues with long dives, because the ZHL formula (paired A/B coefficients matched to a fixed half time) is rather inflexible. When the formula is extrapolated to longer dives, then is tends to go off scale or out of context. Plus if we add GF to the result, it compounds the exaggeration as GF has its own set of issues with expanding times.
VPM-B, on the other hand, is far better at keeping context with longer dives, as the physics behind the models controlling ascent limitations (micro-bubbles), are not bound in the same way as ZHL is. VPM-B calculations are more dynamic and better able to match the dive conditions.
---------- Post added December 15th, 2015 at 05:02 AM ----------
Can it change ZHL Bühlmann into something new? Not really.
The ZHL calculation comprises of 16 (or 32) sets of 3 matched values (a halftime, with a matched A/B value). In order to modify ZHL successfully, one would need to redefine all three. That would result in a whole new algorithm and model. And when its finished, its still a range bound and inflexible design.
But, VPM is more than capable of handling any gas kinetic changes that might come our way, without any real modifications needed. Maybe if the science can come up with enough tested date points, we can have a VPM-C one day
There's a great thread about this over on CCRExplorers with people like Simon Mitchell and David Doolette chiming in.