Manual calculation for accelerated deco

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Again, DecoPlanner was made after Ratio Deco. The chronology doesn't fit your anecdote.



As for the altitude thing - if you know or believe altitude is a factor, account for it. If you believe or know cold is, you account. If you feel dehydrated or exhausted, you account. Not your computer, but you.

A program *like* DecoPlanner. DP is just buhlmann and vpm. Buhlmann for sure came before RD because RD’s baseline was the buhlmann output.

“Account for it” is totally nebulous. Account for it how? By adding time? How much? Where?

No tool exists for civilians that can even somewhat “account” for stressors like cold and tired except for somewhat arbitrarily adding deco time somewhere.
 
I think this is the thread where UTD's ratio deco was debunked as more religious faith than science: UTD Ratio deco discussion
 
You did mean to say after he was fired, didn't you?

Not really. Is it relevant, or just plain old going for the guy instead of the ball?

A program *like* DecoPlanner. DP is just buhlmann and vpm. Buhlmann for sure came before RD because RD’s baseline was the buhlmann output.

I'm saying that using "RD is supposed to mimic DecoPlanner" is an invalid argument, both in and by itself but, more importantly, also against the statement that "there's no science behind it" and, particularly, against the point that RD does more things than purely decompression.

Saying that all RD does, is mimic DecoPlanner, is missing the point.
That's my point.

As olive branches go, I'm not saying that I'm convinced Ratio Deco is more "optimal" at removing N2 from the tissue, purely physiologically, than some "perfect algorithm" (whichever that may be), is. I've never said anything to that effect, actually quite the contrary.
I fully acknowledge that Ratio Deco, from a purely physiological perspective, cannot be "optimal" - even it it were "optimal", it still couldn't possibly be at all depths.

However, I am satisfied that it is more than safe enough, and I find it extremely practical compared to other solutions. That's it.

And I don't need to bash people for diving something else, whichever brand of computer they choose, if any, or whichever algorithm they put their faith in.

And indeed, I haven't.

I think this is the thread where UTD's ratio deco was debunked as more religious faith than science: UTD Ratio deco discussion

Do you have an insight you'd like to share?
 
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At 2.000m, you're looking at ca. 0,8 bar.
That means the delta relative pressure difference on ascending from 3m to 2m across sea level (1,3 bar at 3m) and 2.000m altitide (1,1 bar at 3m), is less than 1,5%.
The impact of that on an ascend is about as significant as a burp.
If that little difference is what's winding you up in terms of decompression, you'd never do a repetitive dive, ever. Or dive in cold water, for that matter.
Besides, you're talking about, say, making a pressure drop from 6,0 bar to 1,0 bar versus making a pressure drop from 5,8 bar to 0,8 bar. The total difference is still 5,0 bar.

Are you really saying altitudes doesn’t matter?

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).

That looks like a big difference in the underlying cause of bubbles.
 
What matters at altitude is not just the difference in total pressure. What matters is what happens to the diver during the dive. At 2,000 meters, the atmospheric pressure is about .8 that of sea level. The water, however, weighs the same at any altitude. That means that a diver at 204 FFW at sea level is at 7 ATA. At 2,000 meters, that diver is at 6.8 ATA--not much difference (less than 3%) at all because nearly the entirety of the total ATA comes from the weight of the water. That means the diver will be ongassing at approximately the same rate as at sea level. As the diver ascends and breathes the same gases he or she would be diving at sea level, the diver offgases at about the same rate. What is different at altitude is that as the diver nears the surface, the lesser air pressure becomes more and more and more significant, with that last 34 feet (1 ATA fresh water) making the most difference. At 34 FFW, the ambient pressure at that altitude is 1.8, compared to 2.0 at sea level--nearly a 10% difference. The biggest difference at all comes when surfacing--about 20% difference. That means the gradient between tissue pressure and ambient pressure, the cause of DCS, is significantly greater at altitude.

Let's look at a different issue during ascent--bubble growth, using Boyle's Law: P1 * V1 = P2 * V2.

Sea Level: Start with a gas volume of 1 whatever (units don't matter) at 204 FFW. Following Boyle's Law, (7*1 = P2*V2), we divide the original pressure (7) by the new pressure (P2) to get the new volume. If a diver were to ascend to the surface, this is what the bubble's size would be at the following depths, which represent 1 ATA changes in pressure: 170 = 1.16; 136 = 1.4; 102 = 1.75; 68 = 2.3; 34 = 3.5; surface = 7. So bubble growth is small at first but expands rapidly near the surface.

At 2,000 meters: Start with a gas volume of 1 whatever at 204 FFW at 2,000 meters. Following Boyle's Law, (6.8*1 = P2*V2), we divide the original pressure (6.8) by the new pressure (P2) to get the new volume. If a diver were to ascend to the surface, this is what the bubble's size would be at the following depths, which represent 1 ATA changes in pressure: 170 = 1.18; 136 = 1.42; 102 = 1.8; 68 = 2.4; 34 = 3.8; surface = 8.5. All the way to 34 feet, the difference is insignificant. From 34 feet to the surface to the surface, though, things change dramatically. At that point, the increase in bubble size is 21%

So how do other algorithms treat the difference? Much of Buhlmann's work was done at altitude, so he had real measures of real divers at altitude on which to base his theories. I just ran a dive to 200 feet for 30 minutes using 18/45 and doing deco with 50% and 100% through Multideco using Buhlmann ZHL 16-C, once at sea level and once at 2,000 meters. The altitude dive called for 8 more minutes of decompression (an increase of 17%), with all of that coming the last few stops, as you would expect from the information provided above.

So Buhlmann's research indicated that a diver at that altitude needed 17% more decompression time than a diver at sea level. Can you explain what it was in UTD's research that led them to conclude that Buhlmann was wrong?
 
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.
 
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So how do other algorithms treat the difference? Much of Buhlmann's work was done at altitude, so he had real measures of real divers at altitude on which to base his theories. I just ran a dive to 200 feet for 30 minutes using 18/45 and doing deco with 50% and 100% through Multideco using Buhlmann ZHL 16-C, once at sea level and once at 2,000 meters. The altitude dive called for 8 more minutes of decompression (an increase of 17%), with all of that coming the last few stops, as you would expect from the information provided above.

So Buhlmann's research indicated that a diver at that altitude needed 17% more decompression time than a diver at sea level. Can you explain what it was in UTD's research that led them to conclude that Buhlmann was wrong?

I wouldn't expect the added stops to be nearer the surface, at all. I would expect them to be deeper, as I would expect slow tissue on-gassing to in this case become less dominant a factor compared to micronuclei expansion management.
Hence dominating a shift in weighting of gradient and deep stops in this case.

If bubble size alone didn't drive the argument, surface tension certainly would.

In either case, it's theoretical unless either of us has a reference to trials that clear the matter up for us. You mention Buhlmann's work. Do you have a link to something of his that supports your logic?

On a sidenote, out of curiosity, which profiles did you land on, for the 60m dive on 18/45 with 50 and 100?
 
I'm afraid @Dan_P doesn't understand altitude diving, but I guess that's ok because RD doesn't either. :(
 
I wouldn't expect the added stops to be nearer the surface, at all. ...//...
Pick a profile that you like. Personal preference, I don't care.

Your chosen profile will become 'compressed' and shifted towards shallower depths when diving at altitude. There is a physical reason for that change.
 
https://www.shearwater.com/products/perdix-ai/
http://cavediveflorida.com/Rum_House.htm

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