UTD Ratio deco discussion

[boulderjohn]

However IIRC, the original premise of not having to compensate for "Lake Tahoe" type dives was that altitude was conserved in the RD method calculation; IOW, the diminished atmospheric pressure at altitude was automatically translated to at depth in absolute atmospheres, so the tissue ongas/offgas rates would be the same with either the same or slightly less inert loading.

I never heard that explanation. If it were true, it would be true of all altitude-based calculations for all algorithms, wouldn't it?

 

[mikeny9]

Both groups made mistakes. When I was with UTD, we were told not to use the average depth feature of the bottom timer, because it included the ascent time. We were taught to check our bottom timers ever so many minutes and keep a running average in our heads. There is no question that they did realize that they had screwed up the ascent rate to the first stop, just as the second group did. The second group is also at fault because they were of the "the slower the ascent the better" school of ascending, which many people have said is the most common error in technical diving--they don't get off the bottom with the urgency they should.

But you missed the point. Both groups made mistakes. Both groups were unaware of the fact that they made the mistakes. The difference is that one group acted according to those mistaken beliefs, and the other group acted according to their computer's correction of their mistaken beliefs.

You can pick two convenient examples that support your claim. In the first group, they were following ratio deco, screwed up (by not following it correctly) and ended up getting bent. In the second group, they screwed up by ascending too slowly, followed their computer and didn't end up getting bent. Therefore, your claim is you shouldn't use RD because if you make a mistake you can get bent, and if you don't follow RD and make a mistake you can't. This is simply not true.

There are several cases where people follow 30/85, 50/80, some other GF, VPM-B +2, or whatever model you want to pick, and winded up getting bent. I can use the same logic you did, pick out two samples, and say the people who got bet using GFs, if they were using RD, they might have adjusted their profile based on the conditions and would not have gotten bent. The logic works both ways. If people screw up, all bets are off whether they are following RD, trying to follow RD, trying to follow a computer, etc. They are rolling the dice, they could wind up ok or end up with a bad hit. To be fair, I also know people who followed RD 2.0 perfectly and winded up with a bend, while several other people doing the same dive were fine. The same is true for any model you want to follow, sometimes it's undeserved, explainable by other external conditions (PFO, etc) and sometimes not.

I completed several hundred dives, including shallow training dives, in my UTD years. I was certified at Tech II. I took my Ratio Deco class from Andrew Georgitsis. That was a long time ago. I am honestly trying to understand what the current thinking is here, and this is your chance to show everyone what that is.

Below you will find two dive profiles from Multi-deco ZHL-16 C with GFs of 50/80, which is what I am currently using. The first is for a simple freshwater dive using 21/35 at sea level, and the second is the exact same dive at 6,000 feet. (I did it with 2 deco gases; I can change it to 1 deco gas if you prefer.) When I was with UTD, we would have done them both the same, but you say things are different now, and UTD will change practices at altitude.

Could you please post what those two dives would look like in current UTD practice? It doesn't have to be you who answer--any of the other UTD instructors reading this thread can fill in the information.

To be clear, again UTD doesn't teach altitude diving as part of ratio deco. I'll play along though, by depth adjusting for 6000 ft elevation and still using RD.

I'm not trained for two deco bottles, and I'm not trained to go to 180' for 30 min. I've completed UTD's tech 1 program (the new tech 1 is the old tech 2), which is max of 160'. Therefore, I'll depth adjust your sea-level dive to a depth of 130' instead of 180', because 130' at 6000ft of elevation is roughly equivalent to 160' at sea level. I'd also have to change the bottom time to 25 min because my training only provides for 30 min of deco, and at 160' I would get 25 min of bottom time and 30 min of deco at sea level.

Dive to 130', 25 min BT, 21/35 for back gas and 50% O2 for deco gas at 0ft of elevation
Note: I'd probably switch to 25/25 and a 100% bottle for this dive, but you kept the parameters the same between the two so I'll do the same. The deco gas is not as ideal as a 100% bottle.

Descend to 130ft at 60 FPM, level off at 130' for 23 min (25 min BT)
Ascend to 80' at 30 FPM
80': Stop for 1 min
70': gas switch to 50%, stop for 2 min
60': stop for 2 min
50': stop for 2 min
40': stop for 2 min
30': stop for 2 min
20': stop for 2 min
10': stop for 5 min

For completeness:
Dive to 130', 25 min BT, 21/35 for back gas and 100% O2 for deco gas at 0ft of elevation

Descend to 130ft at 60 FPM, level off at 130' for 23 min (25 min BT)
Ascend to 80' at 30 FPM
80': stop for 1 min
70': stop for 1 min
60': stop for 2 min
50': stop for 2 min
40': stop for 2 min
30': stop for 2 min
20': gas switch to 100%, stop for 10 min
10': slowly ascend 3-5 min to the surface

Dive to 130', 30 min BT, 21/35 for back gas and 50% O2 for deco gas at 6000ft of elevation

Descend to 130ft at 60 FPM, level off at 130' for 23 min (25 min BT)
Ascend to 80' at 30 FPM
80': Stop for 1 min
70': gas switch to 50%, stop for 3 min
60': stop for 3 min
50': stop for 2 min
40': stop for 2 min
30': stop for 5 min
20': stop for 10 min
10': stop for 5 min

Are these acceptable?

 

[boulderjohn]

I recently talked with a diver/scientist who works with Duke, NASA, and the Pentagon on decompression theory. Yes, astronauts need to avoid getting bent upon ascent to altitude, as do U-2 pilots. We were discussing very high altitude diving, and he explained that there is a lot more to it than you would think. Things that don't make enough difference to be considered in the first few thousand feet of altitude increase become more and more important the higher you go. Just as one example, at very high altitude, the fact that water vapor being exhaled does not compress becomes a factor that has to be considered.

We were talking about a very specific high altitude decompression dive (at 16,000 feet), and he said that there are only about a half dozen people in the world with the ability to plan such a dive. Yet, people think it is just a matter of extending what you do at lower altitudes. For example, if you go to Multi-deco, open up one of the algorithms, and input a dive to 200 feet at 16,000 feet of altitude, you will get a dive plan, a dive plan that is not even remotely in the ballpark of his rough, off-the-top-of-his-head estimate. He was estimating HOURS more deco than the plans you get.

 

[Kevrumbo]

I never heard that explanation. If it were true, it would be true of all altitude-based calculations for all algorithms, wouldn't it?

No John, of course not.

Remember this context is pre-NEDU Study, with regard to the tenets of original RD methods and applied Bubble Model Theory. As the reasoning went, so long as you kept any bubble nuclei/micro-seeds small with the use of deepstops (i.e. using the original WKPP Deepstop Table which had the 75% max first deepstop with 30min past NDL), you could supposedly use the same or similar profiles of RD at sea level or at altitude.

 

[mikeny9]

Yet, people think it is just a matter of extending what you do at lower altitudes.

I would never, ever do that. Unfortunately there is no solution to people not using their head, nor a solution to providing them with a brain they don't have in the first place.

 

[decompression]

I will keep my monkey out of this circus,

but for the sake of info.....same dive profile regardless of elevation.
180' dive, 18/45 or 15/55, 50% and O2 for deco. Set point 200', double BT then adj for depth (dive is 180 so minus 10 min).

180(3)
180-27(30)
120-2(32)
120-1(33)
110-1(34)
100-1(35)
90-2(37)
80-2(39)
70-5(44), 50%
60-5(49), 50%
50-2(51), 50%
40-2(53), 50%
30-10(63), 50%
20-10(73),100%
10-10(83), 100%

BT 27, RT 83, DT 44

You can shape the S curve and O2 anyway you'd like.

This is a RD 2.0 1:2 ratio deco profile, depth range 170-240.

 

[boulderjohn]

I'm not trained for two deco bottles, and I'm not trained to go to 180' for 30 min. I've completed UTD's tech 1 program (the new tech 1 is the old tech 2), which is max of 160'. Therefore, I'll depth adjust your sea-level dive to a depth of 130' instead of 180', because 130' at 6000ft of elevation is roughly equivalent to 160' at sea level. I'd also have to change the bottom time to 25 min because my training only provides for 30 min of deco, and at 160' I would get 25 min of bottom time and 30 min of deco at sea level.

I am very confused by what you did. Did you plan a dive to 160 feet using an equivalent depth of 130 feet, or did you plan a dive to 130 feet?

Here are the Buhlmann plans for a dive to 160 feet for 25 minutes on 21/35 with one deco gas, both at sea level and at altitude. Could you tell me what the new RD plans would be for those two dives? Don't worry about what your personal limitations are--I just want to know what the new RD rules are.

Elevation = 0ft
Conservatism = GF 50/80

Dec to 160ft (2) Triox 21/35 60ft/min descent.
Level 160ft 22:20 (25) Triox 21/35 1.20 ppO2, 74ft ead, 92ft end
Asc to 70ft (28) Triox 21/35 -30ft/min ascent.
Stop at 70ft 1:00 (29) Nitrox 50 1.53 ppO2, 32ft ead
Stop at 60ft 1:00 (30) Nitrox 50 1.38 ppO2, 26ft ead
Stop at 50ft 1:00 (31) Nitrox 50 1.24 ppO2, 19ft ead
Stop at 40ft 2:00 (33) Nitrox 50 1.09 ppO2, 13ft ead
Stop at 30ft 4:00 (37) Nitrox 50 0.94 ppO2, 7ft ead
Stop at 20ft 7:00 (44) Nitrox 50 0.79 ppO2, 0ft ead
Stop at 10ft 14:00 (58) Nitrox 50 0.65 ppO2, 0ft ead
Surface (58) Nitrox 50 -20ft/min ascent.

 

[boulderjohn]

I will keep my monkey out of this circus,

but for the sake of info.....same dive profile regardless of elevation.
180' dive, 18/45 or 15/55, 50% and O2 for deco. Set point 200', double BT then adj for depth (dive is 180 so minus 10 min).

180(3)
180-27(30)
120-2(32)
120-1(33)
110-1(34)
100-1(35)
90-2(37)
80-2(39)
70-5(44), 50%
60-5(49), 50%
50-2(51), 50%
40-2(53), 50%
30-10(63), 50%
20-10(73),100%
10-10(83), 100%

BT 27, RT 83, DT 44

You can shape the S curve and O2 anyway you'd like.

This is a RD 2.0 1:2 ratio deco profile, depth range 170-240.

So, it appears to me that the first stop is still at 75% of the maximum depth, and the S-curve is still in effect. Is that correct?

 

[decompression]

66%.....118......I rounded up

 

[boulderjohn]

66%.....118......I rounded up

My math was pretty shaky.

How about altitude--would you adjust, and if so, how?