The study referred to in this string - published in the March 2017 issue of DHMJ - looks like it took place in early 2014. Since then, UTD revised RD and released Ratio Deco version 2.0 in mid 2016 - which places less emphasis on deep stops ...
Effect of slow compartments size in relation to NDL and DECO
- Thread starter narke
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When they explain integrals they call them "slices" -- I doubt "tissue slices" would work much better, esp. for people practicing (dive) medicine.
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So here is the deal. Computers algorithms - like Sheerwater Perdix, can be adjusted with gradient factors depending on your own personal preference. Likewise, Ratio Deco 2.0 can be shaped depending on your own personal preference. Below is a comparison of two ascents used during the study, and an example of an ascent I calculated using RD 2.0. Please note that I could have shaped my 21-9m stops to look like the RD stops used in the study - but I chose not to - and as far as I know - my shape would also be correct. Also note that the main difference between RD 1 and 2.0 *in this profile* is that 2.0 eliminates the 36m and 33m stops.
Also notice that the main difference between my RD 2.0 profile and the Buhlmann is that mine spends only 5 extra minutes total spread between the 21-18 meter stops - right after switching to ean50.
Disclaimer: I am not a UTD Technical Instructor, and this table contains a possible UTD RD 2.0 tec 2 profile. It is provided as an example only, so do not rely on it for your own personal dive without first studying RD, taking a UTD RD class, and accepting the risk for yourself.
Also notice that the main difference between my RD 2.0 profile and the Buhlmann is that mine spends only 5 extra minutes total spread between the 21-18 meter stops - right after switching to ean50.
Disclaimer: I am not a UTD Technical Instructor, and this table contains a possible UTD RD 2.0 tec 2 profile. It is provided as an example only, so do not rely on it for your own personal dive without first studying RD, taking a UTD RD class, and accepting the risk for yourself.
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victorzamora
Contributor
So here is the deal. Computers algorithms - like Sheerwater Perdix, can be adjusted with gradient factors depending on your own personal preference. Likewise, Ratio Deco 2.0 can be shaped depending on your own personal preference. Below is a comparison of two ascents used during the study, and an example of an ascent I calculated using RD 2.0. Please note that I could have shaped my 21-9m stops to look like the RD stops used in the study - but I chose not to - and as far as I know - my shape would also be correct. Also note that the main difference between RD 1 and 2.0 *in this profile* is that 2.0 eliminates the 36m and 33m stops.
Also notice that the main difference between my RD 2.0 profile and the Buhlmann is that mine spends only 5 extra minutes total spread between the 21-18 meter stops - right after switching to ean50.
Disclaimer: I am not a UTD Technical Instructor, and this table contains a possible UTD RD 2.0 tec 2 profile. It is provided as an example only, so do not rely on it for your own personal dive without first studying RD, taking a UTD RD class, and accepting the risk for yourself.
Do you mind providing the bottom time, bottom depth, and deco gasses for the profile you created? I tried replicating it with 30/85 and couldn't quite find it. Closest I got was 200ft for 15min with O2 and EAN50.
According to the summary at the link that @Dan_P posted.
A comparative evaluation of two decompression procedures for technical diving using inflammatory responses: compartmental versus ratio deco. - PubMed - NCBI
The study was 50m for 25:00, using "trimix", 50% and O2, with GF30/85. The summary does not say exactly what blend of trimix they used. When I put the dive parameters through the Subsurface planner, assuming 18/45 for the bottom gas, the result has a first stop at 24m, and a total deco time of 33:00 (i.e. total run time of 58:00), compared to @sigxbill's first stop of 27m and deco time of 30:00.
I ran it through Multi-Deco, just to compare, and got a first stop at 27m, but only for 27 seconds. Total deco time of 32:00.
Definitely not sure where sigxbill got his numbers for the Buhlmann ascent. Maybe because he used GF30/80, instead of 30/85? And what for bottom gas? Anyway, sigxbill's numbers seem close enough for purposes of discussion, assuming 25:00@50m, TX18/45, 50%, O2, and GF30/85.
BTW, the conclusion (from the study link) is:
RD 2.0 may be "new and improved" from RD 1.0, but then, based on recent research, I would use GF50/80 for the Buhlmann option. So, how would those compare? I would bet a dollar that GF50/80 would still produce a shorter runtime AND less "increased secretion of inflammatory chemokines". Only a dollar, though. ;-)
victorzamora
Contributor
Bill messaged me that he was using the profile from the study, which I must have missed. It's 165ft for 25min. When I plug it into DecoPlanner 3.1.4, I get a total of 30min of deco. The only difference I got was 2min at 60ft and 1min at 50ft compared to his 1min at 60ft and 2min at 50ft.
One thing that needs to be brought up is what you mentioned: even 30/80 is considered pretty "deep" by most people. I personally dive 50/70 which gives me a first stop at 70ft and 32min deco. 30/80 is 30min deco with a first stop at 90ft. Bill's RD2.0 profile above is 40min of deco with a first stop at 100ft. RD1.0 above is 42min of deco with a first stop at 120ft.
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Jack Hammer
Contributor
"Standard" gas for a dive to 50m/165' would be 18/45.
victorzamora
Contributor
Maybe RD1.0 and RD2.0 are more similar than they are different. Here they are compared to GF50/70.
This is 5 different profiles:
On the second chart, I think it's pretty clear that 50/70 and 50/80 are pretty similar but 50/70 keeps you in the water longer. Also, it's pretty clear that 30/80 is notably deeper than 50/70 and 50/80 but still NOTABLY shallower than even RD2.0.
This is 5 different profiles:
On the second chart, I think it's pretty clear that 50/70 and 50/80 are pretty similar but 50/70 keeps you in the water longer. Also, it's pretty clear that 30/80 is notably deeper than 50/70 and 50/80 but still NOTABLY shallower than even RD2.0.
Dan_P
Contributor
Is there an admin that wouldn't mind splitting the Ratio Deco discussion into a separate thread, please?
So far, it's wonderfully serious in how it's conducted - but, as has been pointed out, and while both discussions in this thread are very interesting, they are only somewhat peripherally related.
Also, I did promise Simon I'd shut up
As for an ascend schedule on a 25 minute dive to 50m using 18/45 - as were employed in the trials - I'd land on something on the lines of this:
3m - 3
6m - 12
9m - 5
12m - 2
15m - 2
18m - 3
21m - 3
24m - 3
27m - 2
30m - 2
Total 37 minutes.
On a specific note, if it were a 24 minute dive and not a 25 minute dive, the first three stops "by the book" would be 1, 1 and 2 minutes - the extra three minutes there (on the deep stops) would be the same for a dive 14 minutes longer. This is what I mean when I say there's a probable skewering in the results based on the design of the trials (depth and time). The emphasis on deep stops would be significantly smaller if the dive was longer or shorter;
This is the nature of "standard" versus "optimal", both when it comes to deco and when it comes to gas.
For a 30m dive, one can choose a standard gas that is only just within the density parametres one has decided on, but on a 31m dive, choose a lighter one that is - some might say unduly - well within density parametres. The exact same conceptual principle is valid in a deco context, relating to emphasis on deep stops.
If the dive were 1 minute shorter or 14 minutes longer, the RD blueprint would emphasise deep stops significantly less.
On a more general note, the benefits of using a standardized gas or deco blueprint transcend "optimal" decompression. That's why I personally opt for such a solution. It relates to a thought that an ascend doesn't need to be "perfect" (what is "perfect", anyway?), but "safe" will do fine if it brings about other advantages that in turn increase safety in a different fashion (in fairness, that's subject to my view).
For me, I think it's particularly handy that the ppO2 average is the same on CCR and O/C, among other things. But understanding the why of things requires understanding of how every link in the chain fit together.
"Why Ratio Deco?", "Why standard gasses?", "Why a BOV on a rebreather?", "Why Rock Bottom gas planning?"
Any reasonable discussion on either of those questions inevitably relate to the others, and more.
So far, it's wonderfully serious in how it's conducted - but, as has been pointed out, and while both discussions in this thread are very interesting, they are only somewhat peripherally related.
Also, I did promise Simon I'd shut up
As for an ascend schedule on a 25 minute dive to 50m using 18/45 - as were employed in the trials - I'd land on something on the lines of this:
3m - 3
6m - 12
9m - 5
12m - 2
15m - 2
18m - 3
21m - 3
24m - 3
27m - 2
30m - 2
Total 37 minutes.
On a specific note, if it were a 24 minute dive and not a 25 minute dive, the first three stops "by the book" would be 1, 1 and 2 minutes - the extra three minutes there (on the deep stops) would be the same for a dive 14 minutes longer. This is what I mean when I say there's a probable skewering in the results based on the design of the trials (depth and time). The emphasis on deep stops would be significantly smaller if the dive was longer or shorter;
This is the nature of "standard" versus "optimal", both when it comes to deco and when it comes to gas.
For a 30m dive, one can choose a standard gas that is only just within the density parametres one has decided on, but on a 31m dive, choose a lighter one that is - some might say unduly - well within density parametres. The exact same conceptual principle is valid in a deco context, relating to emphasis on deep stops.
If the dive were 1 minute shorter or 14 minutes longer, the RD blueprint would emphasise deep stops significantly less.
On a more general note, the benefits of using a standardized gas or deco blueprint transcend "optimal" decompression. That's why I personally opt for such a solution. It relates to a thought that an ascend doesn't need to be "perfect" (what is "perfect", anyway?), but "safe" will do fine if it brings about other advantages that in turn increase safety in a different fashion (in fairness, that's subject to my view).
For me, I think it's particularly handy that the ppO2 average is the same on CCR and O/C, among other things. But understanding the why of things requires understanding of how every link in the chain fit together.
"Why Ratio Deco?", "Why standard gasses?", "Why a BOV on a rebreather?", "Why Rock Bottom gas planning?"
Any reasonable discussion on either of those questions inevitably relate to the others, and more.
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