Manual calculation for accelerated deco

[Dan_P]

I've made a simple fix (in bold), but agree otherwise.

Agreed.
The total pressure drop is the same - it's the relationship to surface pressure that differs, as you illustrate.

 

[victorzamora]

So in terms of relative pressure change:

A dive to 30m from sea level (1ata to 4ata and 4x increase) is equivalent to a dive from 2000m of altitude to approximately 24m (0.8ata to 3.2ata), correct?

 

[victorzamora]

I'm concluding that I think "more" deep stop emphasis (such as RD, for instance) on an altitude dive along with added shallow stop time, seems reasonable to me, given an increased relative pressure difference.

So I guess here's where the crux of it is: Most of the community believes in SHALLOWER emphasis when diving at altitude. As far as I'm aware, you're alone in arguing that ascent profiles need to stay DEEPER on ascent when diving at altitude. The description of it I read earlier in this thread was that "your ascents get longer and more squashed" when diving from altitude. I believe that description was in comparing the altitude-diving outputs (varying altitude only) using software like DecoPlanner or MultiDeco.

Below is a chart tracking the relative change in pressure that a 1m depth delta causes at different depths. As you can see, below about 15m the lines start converging and there becomes very little delta between them. What that means, to me, is that the deeper you are the less the surface pressure changes what your body feels. As you get shallower, every foot of ascent makes a bigger and bigger difference. This, to me, would indicate two things:

1) Your shallow stops need to get longer.
2) Your deep stops shouldn't really change.

 

[boulderjohn]

So I guess here's where the crux of it is: Most of the community believes in SHALLOWER emphasis when diving at altitude. As far as I'm aware, you're alone in arguing that ascent profiles need to stay DEEPER on ascent when diving at altitude.

That was the statement that floored me earlier. I went through the pressure changes from 204 feet to the surface, comparing sea level to a 2,000 meter altitude. hey show exactly the same pattern as Virotr's graph and practically scream for an altitude diver to make serious adjustments in the shallowest stops. I said something to the effect that this was obvious, but he replied that it was obvious that the correct solution would be add deep stop time. I was stunned, but he offered no explanation why.

Dan (and UTD--his positions are consistent with what I was taught when i was a UTD diver) is the only individual and organization i the dive world that holds several beliefs related to decompression in general and altitude diving in particular. The rest of the diving community bases its beliefs on more than 100 years of research beginning with Bert and Haldane, but I don't know of any scientific studies supporting UTD's beliefs. (Actually, it goes back hundreds of years to Boyle, since my UTD instructor told me that Boyle's Law was wrong.)

My experience tells me that nothing anyone says here will make any difference.

 

[JohnnyC]

 

[lowviz]

So in terms of relative pressure change:

A dive to 30m from sea level (1ata to 4ata and 4x increase) is equivalent to a dive from 2000m of altitude to approximately 24m (0.8ata to 3.2ata), correct?

Insidious. This short question speaks to the heart of it.

One must make the mental gearshift that diving at 0.8 implies that the diver is equilibrated to that pressure. As such, 0.8 becomes the new 'standard atmosphere'. So now, 8, 16, and 24m are your 1, 2, and 3 additional atmospheres.

Where would the tried and true safety stop be now?

 

[Dan_P]

I'm going to say this one more time:

We don't disagree that altitude has an impact on the physiological process of decompression.
It is my belief that it does, and I adjust my altitude dives accordingly.

Do try to disregard John's heuristics-soaked narrative about my position on the matter.

 

[wedivebc]

“
Altitude doesn’t matter. There’s no evidence.

And if there is, then it’s not convincing.

And if it is, it doesn’t matter much.

And if it does, then it’s not RD’s fault.

And if it was, there must have been another factor.
”

same argument flat earthers use

 

[PfcAJ]

same argument flat earthers use

 

[boulderjohn]

Just a reminder for some people who are not used to this that water weighs the same at all altitudes. Total ATA is found by taking water pressure and adding air pressure. Thus, if you are at 30 meters at sea level, your are under 3 ATA for the water and 1 for the atmosphere for a total of 4 ATAs. At 2,000 meters (ignoring the salt water/fresh water difference for this illustration), the diver is at 3 ATA for the water and 0.8 for the atmosphere, for a total of 3.8 ATA.

It is critical that this is understood. The fact that water weight does not change is the reason that there is very little difference between sea level and altitude at depth, but a huge difference to the diver upon surfacing. That is why doing a deep stop at altitude makes little difference compared to sea level, but extending shallow stops is so important. That is why standard dive algorithms have no difference whatsoever in ascents at the deeper depths when comparing sea level to altitude but have a huge difference in the shallow stops.