Explain what you mean by "more conservative GF's." In an earlier post, I spoke of the fact that the common connotations of "conservative" work with GF High, but not so much with GF low. What do you mean by "conservative" in regard to GF low?
Can you do too much deco?
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Not to mention that the Navy ops have a chamber on-site.
I finally occurred to me that you seem to be thinking that the NEDU study tested the Buhlmann algorithm and decided it met a specific standard of safety, and you are quibbling with that standard because Navy divers are more fit. That is not what happened, and that is not what they concluded.
First of all, Buhlmann was not involved at all.
Next, it was a comparative study on the effects of deep stops on ascent profiles. It found that deeper stops are not beneficial. Whether or not deep stops are beneficial has nothing to do with the fitness of the divers--that conclusion would apply to all divers at all fitness levels.
The conclusions you would draw from the study are that it is not beneficial to you to do decompression stops that are deeper than necessary. That conclusion would apply to any algorithm you use. For example, if you were to use VPM (using V-Planner), it would not be beneficial to put the settings on +4 rather than +2, because setting it at +4 would make your first stop deeper.
Note that in that last sentence, I did not use the word "conservative," even though the VPM/V-Planner language says that using a higher setting and stopping deeper is more conservative. That is because we tend to associate the word "conservative" with "safer." It is not safer or more beneficial to use a deeper stop, and so calling it more conservative is deceptive.
Hi
The team did also quite a lot of 60-70 meters range dives in the Philippines and Indonesia using Trimix.
It is not because it is not on the net or public that it didn't not happen
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RedSeaDiver2
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J-Vo
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I know of several divers who no longer put He in there planners or PDCs due to this research.
This ignores the fact that He will on gas faster as the delta partial pressure is higher for He than N2. We start the dives 0 PPHe. My understanding was always that this was the primary mode of the He penalty.
This makes it quite unlikely I will lie to my PDC about He content.
I wouldn't think that's a huge effect since the starting point is immaterial after a few time-constants have elapsed. (This is typically the case for the tissues that will eventually drive the deco.) Further, the 55 minute (for example) He compartment will always lag the 55 minute N2 compartment on uptake precisely because the tissue ppHe starts at 0. (I'm assuming similar inspired fraction of He vs N2. I've found when thinking about this issue that it's worth comparing heliox to nitrox (e.g., 12/88 vs 12/0) as this avoids the "mixing" complication within a given compartment.)
I think the primary issue is actually that for half-times under 30 minutes, the M-values for a given half-time are simply lower for He, mandating a deeper stop. There was a recent thread discussing Powell's statement that there is a reversal in deco "efficiency" for longer dives.
IMO, this is why:
The deeper and longer stops for He (when the sub-30 min compartments are dominating) result in more on-gassing by slower tissues. This is the oft-discussed "deep stop" issue in a different guise. The "helium penalty" is the additional time to off-gas from the next few slower tissues (below the initial controlling tissue), as each eventually becomes the limiting factor.
Eliminating The Helium Penalty - Shearwater Research
Our understanding of decompression science has undergone dramatic revision in the last two years thanks to decompression physiologist David Doolette, Ph.D. and the team at the Navy Experimental Diving Unit (NEDU).
www.shearwater.com
A bounce diver’s decompression requirements depend solely upon the time, depth and level of oxygen (PO2) over the course of the dive regardless of the fraction of helium and or nitrogen used in the breathing mix. In other words the so-called “helium penalty,” i.e. the extra stops and decompression time required when breathing helium mixes on a surface-to-surface bounce dive, does not exist.
Right, that was the conclusion of the study for that one particular profile. Raising the Buhlmann M-values for helium (or pretending it's all nitrogen, thereby using the higher nitrogen-based values) would eliminate the penalty. However, I'm not inclined to test the applicability to other profiles myself.
I'm also curious how the original helium M-values were selected. Why are they lower than the nitrogen value for the faster tissues? I might guess extrapolated from N2, but it's not linear, which seems to rule out something simple like solubility.
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