This post really got my attention, if we enter to a pond at altitude , will have the same water pressure or water column over us at certain depth .The atmospheric air will be lighter, the problem is the nitrogen loading and the off gasing time, i think that first we have to spend time in surface at this new location and waith till we reach equilibrium , before enter to water, if we think that we are saturated at sea level, when we climb, will reduce the pressure on surface, using this concept a dcs at altitude can be worst as we are on a lower atm and our tissues have to adapt to the new atmospheric pressure, if we dive using ndl will have a risk of dcs as our off gassin capacity will be diferent, using tables, or ratio deco or min deco or navy or bulhmann, when diving at altitude your body have to be aconditioned to the new atmospheric pressure, were the bubles can grow faster when you leave the water as your tissues born at a diferent sea level , so on you have to spend more time on the shallow stops ,the main reason is the off gasing capacity of your tissues - i make this observation based on the haldane and bulhman teory, on the ascent strategy chapter .
Yup, acclimatization is an aspect of it - but even when acclimatized, there is another and very significant aspect that plays into it;
Because the pressure at 0m is lower at altitude but the water pressure is the same, there is a greater relative pressure drop on ascend at altitude than at sea level.
This is more pronounced as the diver gets closer to the surface during ascend.
On the face of it, this could be handled in multiple ways, in some conjunction:
1) Shorter NDL-times:
This would be a rather pragmatic approach in that it would solve the issue and work just fine for recreational diving.
It’s an approach that doesn’t try to approach what an “optimal” ascend adjustment might look like, but rather keep (recreational) divers reasonably safe from DCS.
2) Longer shallow stops:
It stands to reason that due to the difference (“delta/altitude difference”) in relative pressure drop during ascend across sea level and altitude being particularly pronounced with approximation to the surface, extending the shallow stops is another reasonable step to make when diving at altitude.
This is a touch less straightforward than adjusting NDL-times (and as far as I know less documented), but has the advantage of scalability (for the mountainous techies) - perhaps the most appeasing step to me would be to relate the relative pressure drop difference across sea level and altitude, and apply that ‘difference ratio’ within the ascend planning (or deco-) framework one would have used at sea level.
3) Stopping deeper:
Whatever deep stop emphasis one opts for, it would stand to reason that it ought be greater at altitude than sea level (due to the greater difference in relative pressure drop).
There are many ways to skin a cat but the core concept of the discussion, is relative pressure drop difference across sea level and altitude.
