Are you really saying altitudes doesn’t matter?
No, I'm not saying altitude doesn't matter. It's just a matter of
theoretical versus
practical - allow me to expand:
I think that altitude does matter, in that as we travel to altitude;
1) at least for a short while, there'll be residual supersaturation
2) there will be increased relative pressure change during ascend/descend compared to diving at sea level.
However, what I think is important to note, is:
1) the residual supersaturation would quickly diminish as we reach equilibrium (consider the practical implications of even travel time to the dive site, compared to tissue halftimes).
2) I would argue the increased relative pressure difference is neglible (more on this below), and in either case this would prompt an
increased emphasis on deep stops. The total gradient is the same. But the relative pressure difference means bubbles would expand marginally faster during ascend)
I mention the latter because Ratio Deco has an increased emphasis on deep stops compared to the algorithms it's actually been compared to, not because I think it has any prctical significance in terms of bouyancy control.
At 2000m the difference between ambient and tissue gas loading will be .2 bar different. Since we might expect a maximum of, say, 1.6 bar tissue loading when surfacing at sea level and so a delta of .6, at 2000m the same surfacing loading will give a delta of .8, 25% more (40% more if you look at the ration of tissue vs ambient).
Either, that's assuming different depths/ascends or one dive across the two altitudes: the diver descends from 1,0 bar ambient (sea level) and ascends to 0,8 (2000m) so there's a supersaturation of 0,2 bar in the tissue.
That's a really unusual scenario. Almost always, there'll be travel by land or air to the dive site at altitude, rather than doing a
2km vertical traverse.
If we're diving at 2000m altitude, we'll either go by land transport (slow, allowing our tissues to desaturate in transit), or air transport (fast, but traveling at even higher altitude, so we'll effectively desaturate prior to arrival anyway).
Or, of course, we'll have been there for some time (no transportation, but we'll have desaturated).
In either case, the tissue gas loading won't be 1,0. It'll likely be closer to or equal to 0,8.
And if it isn't, impacted tissue groups will certainly be the slow ones rather than fast.
Returning to relative pressure difference and your example.
First, the 1,6 bar in your example wouldn't be the same. Comparing apples to apples, that example would be 1,6 at sea level but 1,4 at 2000m from the same dive. So at sea level, you'd go from 1,6 to 1,0. And at 2000m, you'd go from 1,4 to 0,8.
The total difference, or gradient, is 0,6 in either case. It's just that 0,6 is 37,5% of 1,6 but 42,8% of 1,4 and that'll impact by way of bubble dynamics (Boyle's Law).
Again, deep stops.
5,3% difference across the two, and that's on a pop from 6m to the surface.
Relating to bouyancy, we'll be near neutral at this point, so say we have 1L gas to work at this point.
The difference is +5% of 1L on the altitude dive... 5cl.
Effectively, nothing.
In practical terms, I therefore don't think we'll often encounter situations where residual supersaturation has an actual impact.
But, from a theoretical perspective, of course altitude impacts decompression.
I'm fairly sure this is at the heart of the whole debacle, the misunderstanding of
whether there's an impact and
whether it's practically significant.
One says "altitude doesn't matter" (practically, it doesn't matter)
Another hears "altitude doesn't matter" (theoretically, it doesn't matter)
They're different things.
There is of course also some who favor a Schrödinger paradigm in arguing that Ratio Deco at the same time
overemphasises deep stops and
underemphasises deep stops.
