UTD Ratio deco discussion

[CAPTAIN SINBAD]

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A ScubaBoard Staff Message...

this thread was created as a spin off of another thread. The original thread is here

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This could easily get off-topic into yet another discussion about ratio deco. However, I believe the main argument for ratio deco is that there's a big difference in trusting factual things, like depth, time, average depth, current temperature, etc. and trusting something which is computationally precise but questionably accurate like decompression. How you feel and other conditions of the dive may play a role in how much or how little deco you do using a UTD ratio deco approach (I make specific mention of the "UTD ratio deco," because the GUE ratio deco is terribly incomplete and only used in emergencies).

Also, you may think ratio deco is complex math, but to me it's really not. It's fairly simple arithmetic, not complex algebra or anything like that. I recently had a discussion with someone about a dive profile, which initially resulted in them running the profile in their program and it determined they needed to spend 55 minutes at 20' on 100% O2. They didn't realize until I told them that there's something terribly wrong with that plan, and it turned out to be a bug in the software (software was set to calculate last stop at 20'). Computers have their issues as well, as much as I hate to admit it (I'm a software developer by day).

Finally, if you compare ratio deco profiles to 30/85 Buhlmann profiles they are strikingly similar, so I wouldn't let ratio deco be the reason that one should avoid a UTD advanced class.

I respect that and if you read my earlier posts I am have been very accepting of UTD's ratio deco. In the past I have had a greater trust in deep stops and VPM etc. Recently Dr. Simon Mitchell's presentation below shows that Deep Stops are not as safe as they convince people to be and that is why Navy has rejected their use.


Based on this, the most appropriate gradient factor (according to all the research as it stands today) is not 30/85 but 50/70. This is what the likes of John Chatterton have been saying, "Get off the bottom!" How would you accommodate this into Ratio Deco which will still force you to do your first stop much deeper?

Secondly, when we look at the study that Andrew did to prove the effectiveness of RatioDeco seemed to actually show the short-comings of it.

UTD Decompression profile study results published

Even Andrew and the UTD community accepted the results that Ratio Deco is dangerous on some profiles. Instead of abandoning it and moving towards Buhlmann's gradient factors Andrew developed "Ratio Deco 2.0"

Why?

I believe that UTD has a lot to offer to the world if it expands its decompression curriculum to include Buhlmann GF's, VPM and RGBM, GUE Ratio Deco VS UTDs as well as Italian study that led to 2.0 along with the Navy Study and why they are not buying any of it. The purpose should be to create a diver who understands all approaches to modern decompression without the agency pressure to accept one as the gospel truth over the other. If they could do that that would be closer to Andrews ideals of the "thinking diver." It would be GUE with all the good practices people love about it but without the things that they are ticked off / discouraged about.

Just something to think about for the higher level UTD instructors.

 

[mikeny9]

Hi Sinbad, nice to see you on here again . I don't believe the results of the Italian study concluded that ratio deco was more dangerous. The proportion of divers experiencing inflammatory markers relative to those who didn't isn't statistically significant. Even if they were, whether the inflammatory markers should be used as conclusive evidence of DCS is questionable. Dr. Mitchell mentioned on that thread you linked that those markers would be a "poorly characterized indicator" of DCS risk.

That being said, the result of the Italian study did have some minor changes in the UTD ratio deco approach (hence "ratio deco 2.0") and generally has the diver stopping a bit shallower on the deep stop portions of the ascent (66% vs 75%).

One of the reasons UTD does not advocate moving toward a single model like Buhlmann with GFs is because it's just one model, similar to how VPM is another model, and RGBM is another model. The UTD ratio deco is a "strategy," which involves using more than one model, as well as other external conditions such as how you feel, are you doing repetitive dives, the need to change the profile under water because that wreck you thought you'd have 30 ft of relief on doesn't have a bridge anymore or vice-versa, etc. I don't believe decompression is as black and white as my current depth, my average depth, the water temperature, my run time, etc., and has very much a gray area. These external factors are what affect the gray area.

I believe the Navy study you are referring to is the one by Doolette which was performed by NEDU to determine if the Navy should switch from using Heliox to Trimix. The only real conclusion out of that study was that there shouldn't be a Helium penalty in any model like there still is today on Buhlmann GFs. Buhlmann GFs are actually more inaccurate due to the Helium penalty they add. The study doesn't prove or disprove that Heliox is any better than Trimix, it could be, but that's not what the study was trying to look at. It also doesn't prove that Trimix is better than Heliox either. It only proves that Heliox was no worse than Trimix, so the Navy shouldn't need to switch to Trimix. Keep in mind the study was performed for a specific profile too, and people shouldn't conclude this is the same for all depths.

 

[mikeny9]

In a UTD instructional setting, a UTD instructor was criticizing a decision one of the students made during the just completed instructional dive. The student start to respond by saying, "I was thinking that...." The instructor responded by saying, "I need to have you stop thinking and start doing exactly what I tell you to do." I was another student in that class, and I said, "And that is how we at UTD create 'the thinking diver.'"

That, to me, illustrates the paradox inherent in the organizational philosophy of UTD.

Sorry you had that experience. That's definitely not been my experience. I certainly wouldn't call that the "philosophy of UTD" either.

 

[boulderjohn]

I believe the Navy study you are referring to is the one by Doolette which was performed by NEDU to determine if the Navy should switch from using Heliox to Trimix.

No, there as a specific study that compared UTD's version of Ratio Deco to a Buhlmann profile with gradient factors that created a deeper stop than many people are using now, but not as deep as the UTD ratio Deco first stops. The Buhlmann results were significantly better. Other studies suggest that gradient factors leading to a shallower first stop are better than the deeper stop profiles, leading some to assume that if those other gradient factors had been used instead, the difference would have been even greater.

 

[mikeny9]

You're referring to the Italian study that Sinbad linked to? The net effect of "ratio deco 2.0" was basically shallower deep stops, and as a result less time spent to get to 50% of your max/average depth.

 

[CAPTAIN SINBAD]

Hi Sinbad, nice to see you on here again . I don't believe the results of the Italian study concluded that ratio deco was more dangerous. The proportion of divers experiencing inflammatory markers relative to those who didn't isn't statistically significant. Even if they were, whether the inflammatory markers should be used as conclusive evidence of DCS is questionable. Dr. Mitchell mentioned on that thread you linked that those markers would be a "poorly characterized indicator" of DCS risk.

That being said, the result of the Italian study did have some minor changes in the UTD ratio deco approach (hence "ratio deco 2.0") and generally has the diver stopping a bit shallower on the deep stop portions of the ascent (66% vs 75%).

One of the reasons UTD does not advocate moving toward a single model like Buhlmann with GFs is because it's just one model, similar to how VPM is another model, and RGBM is another model. The UTD ratio deco is a "strategy," which involves using more than one model, as well as other external conditions such as how you feel, are you doing repetitive dives, the need to change the profile under water because that wreck you thought you'd have 30 ft of relief on doesn't have a bridge anymore or vice-versa, etc. I don't believe decompression is as black and white as my current depth, my average depth, the water temperature, my run time, etc., and has very much a gray area. These external factors are what affect the gray area.

I believe the Navy study you are referring to is the one by Doolette which was performed by NEDU to determine if the Navy should switch from using Heliox to Trimix. The only real conclusion out of that study was that there shouldn't be a Helium penalty in any model like there still is today on Buhlmann GFs. Buhlmann GFs are actually more inaccurate due to the Helium penalty they add. The study doesn't prove or disprove that Heliox is any better than Trimix, it could be, but that's not what the study was trying to look at. It also doesn't prove that Trimix is better than Heliox either. It only proves that Heliox was no worse than Trimix, so the Navy shouldn't need to switch to Trimix. Keep in mind the study was performed for a specific profile too, and people shouldn't conclude this is the same for all depths.

Hey Mike, Nice to hear from you Mate.

When I was doing UTD the first stop would start at 75% and it did not matter how deep you were and what the rest of the profile would look like. If you had a preference for bubble control models (which I did) this was not anything radical. If you were more tilted to towards Buhlmann gradient factors then the GF low would have to be kept pretty low to justify such a profile. Another thing that bothered me was that the shallowest stop was never increased to compensate for the deep stops.

I do not know how Ratio Deco 2.0 has altered any of this but it seems that UTD has finally accepted that the first stop does not need to be that deep. This means that when I go and dive with my UTD friends they will be changing their ascent strategy to match mine and it wont be the other way around. I believe that this is an intelligent change on their part and shows a willingness to incorporate modern research. The question then is that when UTD releases Ratio Deco 3.0 or 4.0 then how close it would be to what I am already doing?

The Navy study I am referring to was done because the Navy wanted to adopt bubble models instead of dissolved gas. In order to see whether bubble models (And deep stops) had any additional benefit over what they were doing they did this study that is mentioned at 28:00 of that video clip. It all ended with them abandoning Bubble models and sticking to a more traditional profile.

 

[mikeny9]

Ah yes, that study. I think everyone is pretty much in agreement these days that strict VPM isn't so safe. From what I understand, the ratio deco approach maintains some deep stop theory to avoid too large of bubble sizes, much less than a strict VPM. For example, if you shape your O2 window from 70' to 30' and determine you need 1 min stops, but the deep stop table has you maintain 3 min stops, then you'd have to keep 3 min there to avoid too much bubble growth. That's where the "ascent strategy" comes from: they use deep stop theory to get to the O2 window and shallow/slow tissue zones. The approach aims to keep on-gassing of the slows to a minimum but also tries to control the bubble size to some extent.

The deep stops used to start at 75%, but now they are 66%. There is a 75% stop if you exceed NDL by 30 min, but haven't exceeded it by more than 45 min. However, those profiles are impractical for a Tech 1 student because you'd end up with too much deco time and would need a 50% and 100% O2 bottle. Also, when shaping the O2 window, ratio deco 2.0 prefers to add the "stolen" time from the middle to the shallowest (30') stop. So for example, a BT of 30 min at 150' using 50%, your ascent would look like:
Ascend to 100' at 30 FPM
100': 1 min (deep stop theory)
90': 1 min (deep stop theory)
80': 1 min (deep stop theory)
70': <switch 50 %> 3 min (O2 window)
60': 3 min (O2 window)
50': 2 min (O2 window)
40': 2 min (O2 window)
30': 5 min (dissolved gas theory)
20': 12 min (dissolved gas theory)
10': 3 min (dissolved gas theory) (or 20' 10 min 10' 5 min, etc)

I've compared a lot of profiles to my GUE friends and it's very similar to what they come up with in DecoPlanner that I wouldn't have a problem using their profile and everyone I'ved talked to (about 4 people so far) wouldn't have a problem doing the UTD profile either.

 

[boulderjohn]

John, do you feel GUE has the same sort of philosophy? Just curious.

I was a part of UTD for several years. At one point there was only one UTD student in the world farther along in the tech training sequence than I. In contrast, I have only a few real brushes with GUE. Here are some comparisons that I can make.

I must have been considered a real pain in the butt for UTD, because I challenged a lot of the orthodoxy, and I was threatened with expulsion for that, specifically for questioning some of the information in the course materials. (I was saved from expulsion when it turned out I was right.) . The final break came because of a ScubaBoard thread I started. My UTD group did all our diving at altitude, and UTD taught that we were to plan our deco using Ratio Deco exactly as we would at at sea level, because altitude has no effect on decompression. (I believe they still teach that.) Because we had a pretty high incidence of DCS in our small group, I was pretty concerned. As far as I knew, we were the only diving organization in the world that thought altitude was not a factor for decompression. I started a thread in which I described what I just wrote above and asked people for information on altitude and decompression, and I got an email warning me that if I ever wrote anything like that again in a public forum, my name would be turned over to PADI for violating the member standard against making derogatory statements about other agencies. I would thus face disciplinary action from PADI, possibly expulsion, for making such a statement.

I replied that I had not said a single thing against UTD--I had just said our group had had a number of DCS cases (I think 6 at that time), which was 100% true, and I wondered about research regarding altitude. The reply was that in the thread I had failed to mention that in all the DCS cases, there was a reason other than altitude for the DCS. I didn't know that, and I asked what the reason was. They didn't know, but it had to be something else. Why? Because altitude is not a factor in decompression. I should have said that altitude was definitely not a factor in DCS cases in a thread in which I wanted to ask about altitude as a factor in DCS cases. Indicating there was a possibility that altitude was a factor was considered an attack upon UTD as an organization.

At that time, I was put into direct contact with Jarrod Jablonski of GUE, and we had a very interesting and very frank exchange about using Ratio Deco at altitude. He said that Ratio Deco had been designed to recreate the results of one decompression profile in a specific range of depths using standard gases at sea level. he said that if Ratio Deco could not be used at altitude because that mathematical construct would not recreate what that algorithm would produce when adjusted for altitude. So GUE as an organization is different in that way, although I do know an individual GUE instructor who currently teaches students that altitude is not a factor in decompression, so it is not universal throughout the organization.

In that discussion, Jarrod and I also talked about the S-curve in Ratio Deco. I told him that I thought the research upon which that was based was seriously flawed, and the conclusion was dead wrong because it violated Dalton's Law. He had heard that argument and now agreed with it, and he said they were giving the S-curve some thought. Not long after that, GUE dropped the S-curve. I was still in UTD at the time, and I said the same thing to Andrew. After a while, he agreed that the research was flawed, but when the study comparing UTD Ratio Deco to Buhlmann was released this year, I saw that UTD was still using the S-curve. I don't know if it is in the latest version.

About a year ago I did some boat dives with some very died-in-the-wool GUE divers. They planned and executed their dives using personal computers. I don't know how far that practice extends into official teaching, but the UTD people I know are still opposed to any computer usage. If one of their thinking divers were to think computers were useful on a dive, well, I don't think that would go over well.

That is all I can truly say in comparing the two. I have never taken a GUE course.

 

[mikeny9]

John, altitude not having an effect in decompression is definitely a 180 degree turn from what I've been taught in my time with UTD, for what it's worth.

Also regarding S curves, I believe they used to take the stolen time from the middle and equally distribute it to the deeper and shallower sections of the s curve. This is not the case any more, all of the time stolen in the middle is tacked on to the shallower stop, and emphasizes more dissolved gas theory (Buhlmann-style) approach.

 

[boulderjohn]

John, altitude not having an effect in decompression is definitely a 180 degree turn from what I've been taught in my time with UTD, for what it's worth.

So how does Ratio Deco adjust for altitude now?

Also regarding S curves, I believe they used to take the stolen time from the middle and equally distribute it to the deeper and shallower sections of the s curve. This is not the case any more, all of the time stolen in the middle is tacked on to the shallower stop, and emphasizes more dissolved gas theory (Buhlmann-style) approach.

In the study comparing UTD RD to Buhlmann, the S-curve was definitely there as I knew it. The total time for the middle section of the deco was distributed to weight the deeper stops. Stop time did not increase again until reaching the shallow portion.