UTD Decompression profile study results published

[PfcAJ]

I've run it before, but I just did again, just for you.

For 130->90 (on air, GF50/80), I get 70 minute run time.

For 90->130, I get 77 minute runtime.

Since I would use best mix, I ran it again for a more realistic bottom time and gas.

EAN28, GF50/80, 50 minutes BT (25 at each depth)

130 - 90, 109 minutes
90 - 130, 119 minutes

Good. Why do you think the top one is longer? Hint: it's because you're starting your ascent from 130'.

Now do it with the depth as 110 (the avg).

A more realistic dive plan would be to use oxygen for deco and 30/30 or more likely 21/35. That further reduces the difference. I sure as hell wouldn't sign up for a 50min dive at 110' without a deco gas.

Real life stuff. Not make pretend.

You can *always* cook up some goober plan that will have an inordinate about of deco. But for real stuff the difference is negligible.

 

[stuartv]

My point is simply that there is a wide variation in your real world tissue loading depending on how you do your dive. A variation that is not reflected in a plan that is based on an average depth. On-gassing is not linear. So, if you use a tool that is based on average depth, and it produces statistically safe results, then the conclusion would be that there are many cases where it is giving an ascent plan that is way less efficient than what could actually be done safely. Sure, sometimes the difference is trivial. Sometimes it won't be.

When you go to jump Snake River, are you going to guess where to put your ramp and how big to make it, based on your past experience? Or are you going to take every measurement you can from past experience and then build a ramp using precise measuring tools, with a placement and size that is based on the data from past experience?

Either method still allows for application of past experience to modify the plan. One way just uses a more simplistic method to get to the baseline that you then modify and the other uses a more sophisticated and precise (and generally more efficient) method to get to the baseline (which you can then modify). You rely on your electronic device to calculate your depth and average depth. I rely on mine to do some additional calculations for me.

 

[PfcAJ]

My point is simply that there is a wide variation in your real world tissue loading depending on how you do your dive. A variation that is not reflected in a plan that is based on an average depth. On-gassing is not linear. So, if you use a tool that is based on average depth, and it produces statistically safe results, then the conclusion would be that there are many cases where it is giving an ascent plan that is way less efficient than what could actually be done safely. Sure, sometimes the difference is trivial. Sometimes it won't be.

When you go to jump Snake River, are you going to guess where to put your ramp and how big to make it, based on your past experience? Or are you going to take every measurement you can from past experience and then build a ramp using precise measuring tools, with a placement and size that is based on the data from past experience?

Either method still allows for application of past experience to modify the plan. One way just uses a more simplistic method to get to the baseline that you then modify and the other uses a more sophisticated and precise (and generally more efficient) method to get to the baseline (which you can then modify). You rely on your electronic device to calculate your depth and average depth. I rely on mine to do some additional calculations for me.

I use a computer too dude.

The neat thing about it is that it's always within a minute or two of what I expect it to be. I'm not married to the device, and I can function just fine without it.

 

[ajduplessis]

If the only tool you have is a hammer, everything looks like a nail.

True for narrow-minded individuals....

 

[stuartv]

I realize that my posts have been coming across as "argumentative toolbag". I am going to shut up now, go dive more, and wait for the Light of Experience to shine its loving gaze upon my countenance. Thank you to those of you who put up with me instead of just putting me on Ignore.

 

[RainPilot]

I realize that my posts have been coming across as "argumentative toolbag". I am going to shut up now, go dive more, and wait for the Light of Experience to shine its loving gaze upon my countenance. Thank you to those of you who put up with me instead of just putting me on Ignore.

Just living up to your title, Stuart...

Seriously, I do like the conversations your posts bring up. Every time i think I know whats what I get a reset from someone with a load more experience than me.

Its the main reason I'm on this board.

 

[decompression]

Keep up the challenges Stuart.......keeps everyone from getting stagnant. Me included.

 

[Michael Guerrero]

then the conclusion would be that there are many cases where it is giving an ascent plan that is way less efficient than what could actually be done safely.

I think you're bringing up two different things here. What is efficient and what is safe are not the same. Tech divers I know would describe efficient as that ascent profile which gets you out of the water in the least amount of time while incurring an acceptable level of risk of DCS. And those same divers would say that the safest ascent profile is one that gets you out of the water with the least risk of DCS.

These are two very different goals. The first is readily achievable with techniques like RD (which I don't use and believe is less efficient than other methods) that get you out of the water in an acceptable period of time with a demonstrably (based on the number of people who use this kind of profile successfully) acceptable level of risk for many. Same can be said for other bubble models.

The second would have you on surface-supplied gas for dozens of hours in the shallows while you reduced the chances of DCS to nil. If you watch serious researches in this field give presentations you will see them make this point often. Some methods are practical but subject to chance, others are impractical but certain.

So, there are many ways to get yourself within the acceptable envelope of relatively safe and relatively efficient. RD probably achieves that for dives within it's design parameters (not super deep or super long). Buhlmann is also good (and what I use, though modified with GFs) for dives within its empirically tested parameters.

What I see with your posts, time and time again, is you've circumscribed your views based on the narrow parameters in which you were trained--you've boxed yourself in. I think what you said in your last post might be the best thing you could do. Dive, dive, and dive some more. Gain an appreciation for the variance that exists in this clearly imperfect hobby of ours, and then understand that the vast majority of us are operating within an empirically-derived envelope of safety that encompasses dive parameters sometimes considered "dangerous" by others. The bubble modelers don't all die, the dissolved gas-ers don't all die. Human physiology is varied between subjects, which may account for successful vs. unsuccessful outcomes with the same parameters.

The more you dive, the more your feel for the in-exactitude of this hobby (not a sport) will develop.

Safe diving,
Mike

 

[Kevrumbo]

Don't you select your Standard Gases based on a target depth, where there is a list of depth ranges? So, you choose your SG based on the depth you are planning to dive to, by consulting a table of gases?

How is that better? . . .

I haven't had the formal training on SG and RD, but to an outsider, it SEEMS like the only real justification for standard gases is that you have learned to plan your dive using RD and RD depends on them. I.e. the tool you are using forces you to accept limitations on the gases you can use. All the other "reasons" I've ever seen or heard just seem to be rationalizations piled on top of that.

Ease of blending? Hey, if you're in a situation where ease of blending makes a certain gas preferable, the Best Mix approach will totally accommodate you choosing your gas based on that - it just wont' require you to choose that gas. Personally, I have never done a dive where that made one ounce of difference. When the gas I want isn't what is banked at the fill station I'm at, I request a custom blend and it doesn't make it any harder or more expensive for me whether I choose a custom blend that is a standard gas or a custom blend that is my own requested concoction. However, I can see where it could be a valid concern if you're taking some big bottles, a whip, and doing your own fills on site. Then, like I said, you can choose to use a mix that is the same as a standard gas if you want to. So, Best Mix doesn't have any disadvantage there. . .

Cost? You choose to use a deco method that seems to be quite clearly one that produces longer, slower ascents than commonly accepted modern, computer-based ascents produce. How much extra helium are you using and how do you factor that into your cost analysis? . .

I haven't done a dive on best mix yet where I didn't factor possible alternative sites into the planning. That was part of the training. Best mix is "best" based on a lot more factors than simply the planned maximum depth of the planned, first choice dive site.

MOD ranges of
UTD Standard Mixes @ 1.2ATA ppO2:
Eanx32: 28m
25/25: 38m
21/35: 47m
18/45: 57m
15/55: 70m
12/60 (or 10/70): 90m
10/70: 110m

So at a bottom gas working ppO2 of 1.2 ATA, the END of the Standard Mixes list above are all at 30m or less and with Gas Densities less than 6 g/L.

Simplicity (easy to use base proportional recipes -really don't need blending software):
Standard mixes can be optionally made by blending banked Eanx32 with Helium --i.g. Recipe for every 100 bar of 21/35: add 35 bar of He and top-off to 100 bar with Eanx32. For every 100 bar of 18/45, add 45 bar of He and top-off to 100 bar with Eanx32 etc. Or with Air top-off add 14 bar Oxygen for every 100 bar of Eanx32; or 12 bar, or 9, 8, or 7 bar of Oxygen with the requisite Helium for every 100 bar of 25/25, 21/35, 18/45, or 15/55. http://www.nowdive.dk/images/std gasses.pdf

Practicality:
An Expedition Diveboat Eanx32 top-off of a set of half-full 18/45 doubles & stages used on an initial dive yields a 25/23 mix [25/25] for a repetitive dive; or Eanx32 top-off of half-full 15/55 yields 23/27 [25/25]; or on half-full 10/70 gives roughly 21/35.

Using Standard Gases is better -the motivation is to work it all out smarter not harder. . .

Here's a simple example and strategy, for a novice Open Circuit Tech diver with double AL80's (twinset 11L cylinders) on a first time dive beyond 39m, with practical & economical use of only the standard mixes of 21/35 and Eanx50:

At a setpoint 150'/45m for Ratio Deco 1:1 Schedule, one 40cf/5.5L Deco Bottle of 50% should safely cover a total deco profile time of 20 minutes (deco RMV of 0.6 cf/m or 17l/m). So the pre-dive "insta-profile" depth & bottom time choices, using RD rules (i.e. adding 5min deco for every 10'/3m you go over the setpoint of 150'/45m, and subtracting 5min for every 10'/3m interval less than the setpoint), calculated out like this:

130'/39m for 30min;
140'/42m for 25min;
150'/45m for 20min [RD 1:1 setpoint]
160'/48m for 15min
170'/51m for 10min

(Choose one of the above for a square profile at the particular depth of interest, or stay around the average depths of the 1:1 setpoint).

The Ratio Deco Ascent Profile and total time on Nitrox 50% is the same (20min) whichever depth and corresponding bottom time you choose above. The deco stop times in minutes starting at 70'/21m with 10'/3m interval stop depths ascending to the surface has a progression like this: 2,2,2,2,2,10 and finally slow 1m/min (3'/min) ascent to surface. Alternatively, this is one simple and easy back-up deco profile for the novice tech diver's wet notes, if the dive computer craps out and all that's left is a back-up bottom timer.

 

[boulderjohn]

(which I don't use and believe is less efficient than other methods) that get you out of the water in an acceptable period of time with a demonstrably (based on the number of people who use this kind of profile successfully) acceptable level of risk for many. Same can be said for other bubble models.

All decompression algorithms, going back to Haldane, work to some degree because they are within a range of strategies that will get a percentage of people out of the water without getting bent. That does not make all of them equal. The percentages of all the ones being used are high enough that the odds are very much in your favor of getting out of the water OK, and if you have had a pretty good track record, it is easy to say "it works for me!" That kind of thinking, though, leads to a logical trap--because you have survived doing what you are doing, you are reluctant to make an objective comparison to see if something different might be better.

I used to see this kind of thinking a lot when I was a staff developer trying to get teachers to use new instructional methodologies that would improve student achievement. Most had the "works for me" mentality about the obsolete and ineffective methods they had been using. "Works for me" included statistically miserable results, and the fact that other methods have been demonstrated to produce far better results was completely ignored. "Works for me," they would say. Then they would say, "If it ain't broke, don't fix it," a mindless phrase that glorifies any refusal to make improvements.