UTD Decompression profile study results published

[dmaziuk]

Correct observation but wrong conclusion imo. If you have have to pad a model with an arbitrarily chosen variable you should discard the model or at the very least change it to make it describe reality a bit better.

By "arbitrarily chosen variable" you mean gradient factors, one assumes?

 

[Kevrumbo]

Correct observation but wrong conclusion imo. If you have have to pad a model with an arbitrarily chosen variable you should discard the model or at the very least change it to make it describe reality a bit better.

There is no "right or wrong" conclusion in practice: Qualitatively and strategically, you do as much shallow deco time as you need to ensure surfacing with slow tissue tensions below critical supersaturation levels (in other words, if there are post-dive sub-clinical symptoms like extreme fatigue and/or the "niggles" (or worse -overt & acute DCS) then that's our only usual "uh-oh" sign indicating not enough O2 deco shallow) -how much additional deco time that is on top of the calculated value of whatever model algorithm chosen to generate the decompression schedule is "arbitrary" and depends on the individual along with other factors, such as residual inert gas tissue loading stress over consecutive days of deco dives, water temperature & hypothermia, physical exertion, CNS OxTox exposure etc.

. . .Getting off the bottom (that is, skipping the deep stops) can reduce tissue loading in intermediate and slow tissues. No matter what is done at depth, prolonging shallow stop time is effective at reducing VGE in individuals predisposed to develop them. Other strategies might work, but I am most impressed by those based on credible evidence. I call prolonged shallow stops really cheap insurance.

Neal Pollock Ph.D

https://www.ccrexplorers.com/community/threads/diving-tooh-carefully.18348/page-18#post-178445

Objectively, I think just in general, the above advice from Neal Pollock is a practical option and good "cheap insurance" for any deco algorithm in use, and especially a solution for anyone still choosing to use applied bubble/dual phase theory like Ratio Deco.

By "arbitrarily chosen variable" you mean gradient factors, one assumes?

At least with a gas content model and a Shearwater Petrel/Perdix with Buhlmann GF's, you can have some relative quantifiable reference value to de-emphasize the deep stops and extend out the O2 stops as an option as well -for example start with 40/70 or 50/80 for day one of a multi-day dive trip, and keep that setting or optionally adjust GFHi to a lower value for conservancy as needed -either pre-dive or realtime during the dive if conditions change (i.g. physical exertion, hypothermic stress etc) -for subsequent dives on each consecutive dive day.

 

[Ayisha]

I'm thinking that it might be prudent for GUE to evaluate changing the name from RD to something else since it's been appropriated so badly and people confuse the two, even scientists.

 

[StefinSB]

By "arbitrarily chosen variable" you mean gradient factors, one assumes?

You assumed wrong. I meant Kevrumbo's arbitrarily added shallow stops to Ratiodeco.

 

[Centrals]

I'm thinking that it might be prudent for GUE to evaluate changing the name from RD to something else since it's been appropriated so badly and people confuse the two, even scientists.

If GUE had patented the name in the beginning including DIR then there won't be any confusion.

 

[barth]

I'm thinking that it might be prudent for GUE to evaluate changing the name from RD to something else since it's been appropriated so badly and people confuse the two, even scientists.

When I did Tech1 last year there was no RD. There was pragmatic deco.They did change the name.

 

[huwporter]

By "arbitrarily chosen variable" you mean gradient factors, one assumes?

There is some truth in this. I didn't appreciate exactly how much of a kludge (and how non-'magic') gradient factors were til I programmed my own implementation. I can think of at least a couple of better ways of implementing the same concept.

 

[atdotde]

Just for the fun of it (and to complicate matters), I ran the UTD RD profile through the Subsurface dive planner:

Turns out, with GFs set to 30/80 this ascent is ok (as in: never violates the ceiling).But only barely: If you lower GFhigh by a bit or slightly mess with the timing of the first gas switch to EAN50 you violate the ceiling in the final ascent. So, from the point of view of Bühlmann with GF, you would not expect any more DCS symptoms as if you let GF 30/80 directly compute your ascent.

For comparison, here is the latter plan (note well the different time scales on the time axis!):

 

[stuartv]

Agreed, its a practical get out of the water approach for a change in plan or whatever. I personally use 2 computers but can buy the idea that others prefer "simple" (ok, subjectively) rules that they can use too, and it seems a tool I'd like to have for that really bad day.The comparison graphs (to me) support that view, thanks.

-Mark

2 computers - buy 2 computers. Use 1 to tell you your ascent. If it breaks, use the other one to complete your ascent. If they both break, follow your buddy.

Ratio Deco - buy 2 bottom timer devices. Use your brain and 1 bottom timer to tell you your ascent. If the BT breaks, use the other to complete your ascent. If they both break, follow your buddy.

Which one is "simple"?

For the RD proponents, if they dive with at least one of their 2 BT devices being a completely mechanical device that tells them time and depth, then I can accept and respect their protocol. But, anyone who says "I can't depend on a computer because it's an electronic device" and then dives with 2 electronic bottom timers, well, I feel like they have really drunk the Kool-Aid. ESPECIALLY if they are using one of those electronic devices to tell them their average depth (a value the BT CALCULATES) and then calculating their ascent based on that.

There was one post that almost made some sense to me. The poster said they were cheap and didn't want to spend $2K on computers. I can certainly understand that. But, you can buy a brand new DR Nitek Q for $400 that is a multi-gas trimix computer. So, for $800, you can do whatever tech diving you want, with 2 fully capable computers. If you can't afford the difference between 2 bottom timers and 2 DR Niteks, then, really, you probably can't afford to go tech diving anyway.

I think RD (in the form I understand GUE to employ it) is cool. Doing your dive plan and having an idea of what the ratio of deco time to bottom time is certainly can't hurt. Being able to apply that knowledge to sanity check the ascent calculated by your dive computer is nice.

But, I think the NEED for it anymore is pretty much like the NEED for OW students to learn how to use tables. I.e. the notion that it is NEEDED is simply outdated.

 

[AlexL]

But, you can buy a brand new DR Nitek Q for $400 that is a multi-gas trimix computer.

I was actually just looking at a Nitek, and when my LDS called DR to see about a price match and delivery time, they were informed that its been discontinued for a while now. apparently once they're out of stock at DGX, that's it.