My Journey into UTD Ratio Deco

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CAPTAIN SINBAD

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Woodbridge VA
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Ok … so after reading all the back and forth exchange on ratio deco, I decided to sign up for UTD Technical-1, do a few dives with Ratio Deco and then come back here to state my opinion about this “dangerous and controversial” practice that is taking so much flak. I will be the test-rat of my own experiments and this blog which I plan on keeping as an open diary for everyone to see, will be updated with my progression as well as my own thoughts as they evolve through the course. As I move into this journey, I also invite the whole scubaboard to come with me on here as if they were doing it.

I am already certified for decompression diving to that depth and I am presently doing those dives using dive computers, desktop software and I also consult conventional tables occasionally. UTD Tech-1 will therefore be more of a linear training experience than an upward one. You may ask what is in it for me? To be honest, I am not sure. It will give me first-hand experience with one of the most (if not the single most) controversial and misunderstood issues in diving.

I take into this class a few concerns of my own which I state below.
  1. Applying ratios at altitudes: This has been mentioned here a number of times. I believe I even read an article by George Irvine understating the importance of adjusting to altitudes. I had the chance to briefly discuss this with a UTD instructor and she said that she was not trained for altitude diving but she believed that Ratio Deco tables would have to be adjusted for altitudes. Altitude diving is not in Tech-1 but I will still bring it up.
  2. Depths and Exposure times where ratios fall apart: There has to be some external way of understanding the departure point where following fixed ratios is causing you to deviate from safe-zones that exist between two different algorithms.
  3. Spisni study and its interpretation by UTD: This showed that the initial assumption that UTD as well as the bubble modellers had about deep stops being more effective than buhlmann ascents was wrong. It was partially acknowledged by UTD and the first stop was increased from 75% depth to 66% depth but the 66% depth is till “deep.” For reference, please see: UTD Decompression profile study results published
  4. Dropping gradient factors on repetitive diving: If you are doing repetitive diving on consecutive days, then it may make sense to drop gradient factor hi as the days progress and then to allow a full day of recovery before resuming again from the higher gradient factor. How would a ratio deco diver accommodate this?
  5. The UTD min-deco table is the same for Nitrox 32 as well as 25/25. This is looking to be dangerous on 25/25 because if you have a gas mix that is 25% oxygen and you are applying limits that are calculated for 32% oxygen then that is a 7% more oxygen then what that table is originally meant for. GUE uses 30/30 as their standard gas and they were using it for a table that is for 32% so that is a 2 percent deviation but if you are using a standard mix of 25 and your table is the same as 32 then the difference is significant (IMHO.)
  6. Mental task loading specially when dives go wrong: I have used RD min deco-table for a few test dives and I did not find the mental depth averaging to be overwhelming. It was simple block mathematics which seemed pretty hard to mess up on. I would love to expand further into this concept on dives with more complicated profiles and also when you have accidentally exceeded the limits of the memorized min-deco table.
Lastly, why do it? In the age of dive computers, what is the advantage of turning your mind into a dive computer which runs only on standard gases?

If I am still missing any of the criticisms of ratio deco then please let me know so that I may add to the above list. I am making this journey with an open mind and I hope that the readers and participants who follow me here will do the same. Let us be honest with ourselves. Decompression is still a scientific mystery so this is not meant to be a thread where one prophet logs on to burn the other false ones at the stake. There are so many other threads where that is already happening. Instead I am hoping that this will be a thread that every single person will be able to follow and say that they learnt something that they did not know before be is positive or negative.

As this blog progresses, each of the above may generate so much discussion that moderators may have to branch them into their own threads just so that you can follow whatever bothers you the most. Everyone’s opinion is welcome and appreciated. A few whose opinions I would love to hear are:

@Dr Simon Mitchell
@boulderjohn
@Dan_P
@Kevrumbo
@PfcAJ
@TBone
@rjack321
@Doppler (Steve Lewis but I think he dives more and logs less which is why he is so happy.)

Many thanks,

Sinbad.
 
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I would be curious to hear what you learn about use of Standard Gases.

From what I can tell, the only benefit to diving them (not talking about possibly benefits to logistics, like convenience of blending) is that they allow you to then use RD. Ergo, if you're not using RD, there is no reason to limit yourself to Standard Gases. E.g. I'm diving Cozumel and the dive operator supplies me EAN32 for the first dive and EAN36 for the second. I can't see any advantage to insisting on a "Standard Gas" instead - unless I require a Standard Gas in order to support my use of RD.
 
I would be curious to hear what you learn about use of Standard Gases.

From what I can tell, the only benefit to diving them (not talking about possibly benefits to logistics, like convenience of blending) is that they allow you to then use RD. Ergo, if you're not using RD, there is no reason to limit yourself to Standard Gases. E.g. I'm diving Cozumel and the dive operator supplies me EAN32 for the first dive and EAN36 for the second. I can't see any advantage to insisting on a "Standard Gas" instead - unless I require a Standard Gas in order to support my use of RD.
Using standard gases allows you to quickly memorize and identify trends in deco, reduces confusion in bottle marking, simplifies dive planning, gives you the ability to create permanent tables, plus the obvious logistics advantages.
 
Using standard gases allows you to quickly memorize and identify trends in deco, reduces confusion in bottle marking, simplifies dive planning, gives you the ability to create permanent tables, plus the obvious logistics advantages.

I am really looking for what Sinbad gets out of his class.

But, since you mentioned it, it seems to me that there are no logistical advantages to Standard Gases. Only disadvantages.

Why would I say that? Because, example: I'm planning a dive to 150'. I dive Best Mix. If there is a logistical advantage to using 21/35 (a Standard Gas) - say because it will be easy to blend - then I can choose to use that. Best Mix enables me to use whatever gas makes the most sense for my dive. Advantage in logistics: Neither.

Example 2: I'm diving recreational dives on wrecks in NC. The shop banks EAN30. I dive Best Mix, so I can use that, no problem. If I require a Standard Gas, then I have to get a custom blend done. Advantage in logistics: Best Mix.

It is impossible to compare a system that allows any gas to a system that has a limited selection of gases and say that the limited selection has an advantage in logistics. Best Mix can use any gas that Standard Gas offers, therefore there is NO logistical advantage to Standard Gas. Only the disadvantages of being limited to certain gases.

As I said in my previous post, the only real reason I can see for limiting oneself to Standard Gases is to facilitate using RD. But, I am looking forward to hearing what Sinbad learns in the class he takes - especially if he is able to ask about this topic (without getting kicked out).


Statements about Best Mix diving that imply that Best Mix REQUIRES the diver to use the gas that exactly gives a ppO2 of 1.4 at the planned max depth (or any other requirement) are really just statements that seem to me to reflect ignorance of anything other than Standard Gases. Or an agenda to promote Standard Gases, even if it means saying things that are not true. Best Mix does not dictate use of any one specific gas (or 2 or 3 choices) for a given dive, and that is the fallacy that leads to statements like Standard Gases have "obvious logistics advantages."
 
I loaded my truck last night for a 190’ profile dive.

This morning as I was pulling out of my driveway I got a text stating that the plan was changed. No big deal, I just snagged 240 gas and a 120 deco bottle. No need to try and fill tanks for a super specific profile. Super handy.
 
Using standard gases allows you to quickly memorize and identify trends in deco, reduces confusion in bottle marking, simplifies dive planning, gives you the ability to create permanent tables, plus the obvious logistics advantages.

I am really looking for what Sinbad gets out of his class.

But, since you mentioned it, it seems to me that there are no logistical advantages to Standard Gases. Only disadvantages.

Why would I say that? Because, example: I'm planning a dive to 150'. I dive Best Mix. If there is a logistical advantage to using 21/35 (a Standard Gas) - say because it will be easy to blend - then I can choose to use that. Best Mix enables me to use whatever gas makes the most sense for my dive. Advantage in logistics: Neither.

Example 2: I'm diving recreational dives on wrecks in NC. The shop banks EAN30. I dive Best Mix, so I can use that, no problem. If I require a Standard Gas, then I have to get a custom blend done. Advantage in logistics: Best Mix.

It is impossible to compare a system that allows any gas to a system that has a limited selection of gases and say that the limited selection has an advantage in logistics. Best Mix can use any gas that Standard Gas offers, therefore there is NO logistical advantage to Standard Gas. Only the disadvantages of being limited to certain gases.

As I said in my previous post, the only real reason I can see for limiting oneself to Standard Gases is to facilitate using RD. But, I am looking forward to hearing what Sinbad learns in the class he takes - especially if he is able to ask about this topic (without getting kicked out).

Statements about Best Mix diving that imply that Best Mix REQUIRES the diver to use the gas that exactly gives a ppO2 of 1.4 at the planned max depth (or any other requirement) are really just statements that seem to me to reflect ignorance of anything other than Standard Gases. Or an agenda to promote Standard Gases, even if it means saying things that are not true. Best Mix does not dictate use of any one specific gas (or 2 or 3 choices) for a given dive, and that is the fallacy that leads to statements like Standard Gases have "obvious logistics advantages."
MOD ranges of
Standard Mixes @ 1.2 bar average ppO2;
Eanx32: 27msw
25/25: 39msw
21/35: 48msw
18/45: 58msw
15/55: 72msw
12/60 (or 10/70): 90msw
10/70: 110msw

At the above MOD ranges for each particular Standard Mix @ 1.2 bar average ppO2, the END (O2 plus N2) are all 30msw or less; and Gas Densities less than 6 g/L to reduce WOB Carbon Dioxide retention at that depth. In other words, the three critical parameters of ppO2, END and Gas Density are all automatically covered with an appropriate Open Circuit Standard Bottom Gas chosen for a particular operational depth.

Standard Mix Bottom Gas Trimix can be easily made on expedition by optionally blending banked T-bottles of Eanx32 with Helium -->i.g. The recipe for every 100 bar of 21/35: add 35 bar of He and top-off remainder to 100 bar with Eanx32. For every 100 bar of 18/45, add 45 bar of He and top-off remainder with Eanx32. For every 100 bar of 15/55, add 55 bar of He and top-off remainder with Eanx32. For every 100 bar of 12/60, add 60 bar of He and top-off remainder with Eanx32. For every 100 bar of 10/70, add 70 bar of He and top-off remainder with Eanx32, etc (Do you see and understand the pattern here @stuartv? No fancy smartphone blender app needed -just a straightforward "cookbook" application of the above, a transfer fill whip & pressure gauge and an O2 analyzer). [A full fill to 230 bar for a twinset of 12L/HP100's cylinders for example, just simply multiply the above per 100 amounts by 2.3 (or similarly for a full fill to 3442 psi in US Imperial Units, multiply by 34.42)].

Finally a practical logistics example:
An Expedition Diveboat with banked Eanx32 and strategically topping-off a set of half-full 18/45 doubles & stages used on an initial deep dive yields a 25/23 Triox (close to Standard Mix 25/25) for a shallower repetitive divesite; or Eanx32 top-off of half-full 15/55 doubles & stages yields 23/27 (again close to 25/25); or Eanx32 top-off on half-full 10/70 gives 21/35 Standard Mix. With this top-off strategy and retaining the use of Standard Gases, you can still implement the Ratio Deco/Min Deco Method on a repetitive dive. . .
 
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UTD Tech-1 training covers how to blend UTD standard mixes. I am assuming that if you are into DIR standard mix diving then you will be mixing your own brew and that is why UTD tech 1 training includes a chapter on how to do it.
 
UTD Tech-1 training covers how to blend UTD standard mixes. I am assuming that if you are into DIR standard mix diving then you will be mixing your own brew and that is why UTD tech 1 training includes a chapter on how to do it.
Any shop can blend a standard gas for you just the same as any other mix
 
Any shop can blend a standard gas for you just the same as any other mix

True but doesnt hurt to know how to do it if you are that type of person :)
 
When I took the RD class with AG he tried to make the point that small differences in depth or time can be insignificant to the plan. He did not round up as you do when planning with a dive table. Just speculating but he may have waived away a few thousand feet of altitude change as an insignificant pressure change without considering what would happen with five or ten thousand feet of altitude change. That was the approach over ten years ago it may have changed.
 
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