Manual calculation for accelerated deco

[hanymamdouh]

If you mean decompression simulation and the "internals" of deco algorithms, these topics are discussed in my book Deep Into Deco. Excerpts from the book (in the form of articles) are often published in Tech Diving Mag (free publication; link in the sig line).

Dear Mr. Aseer, thanks for the reply. I'm welling to get the book and to have a personal meeting with you if possible.

 

[Red Sea Shadow]

Dear Mr. Aseer, thanks for the reply. I'm welling to get the book and to have a personal meeting with you if possible.

Most welcome.

 

[hanymamdouh]

Thanks all for your help and support. I'm still working on it, and here are my findings up to now:

Already Done:
1. I studied Decompression Theory to find rate for tissue absorption of inert gases (Ref. Decompression Theory - Jaap Voets)
2. Using M-Value for Buhlmann ZH-L15A table, I created Excel sheet for M-values for 16 tissue compartments for depths from 0 to 90m (Ref. Understanding M-Values - Erik Baker)
3. I plotted M-Values for 16 compartments on Patm - Ptissue diagram
4. Using Haldane Equation, I can get Tissue Pressure against dive time, hence plotting it on the Patm-Ptissue diagram

Still working on this:
5. From this point, I can predict decompression time and rate, ensuring that all Ptissue drops occurs within decompression zone (between M-Value and Ambient Pressure Line)
6. Using Haldane equation again, I can accelerate the deco by reversing the process on the newly selected profile.

 

[rossh]

Hi all tecies,

Regarding decompression; I want to understand how to calculate accelerated decompression. In other words; using Buhlmann's tables I can calculate decompression stops for a dive if back gas is air. In case of Nitrox; I simply use EAD with Buhlmann's tables to figure out deco stops. But in real world; we use rich mixes (EANx50 and higher) to accelerate decompression at shallower depths (12, 9, 6 meters). Simply I can use computer software like MultiDeco to calculate the profile, but I'm eager to know exactly how to calculate this acceleration by hand.

Thanks so much.

Accelerated deco occurs when the combinations of all inspired and tissue pressures (immediately after the gas switch), compare to the allowable gradient (supersaturation): this provides a temporary lull in pressures allowing for the profile to be sped up briefly.

In the ZHL / VPM gas kinetic formula, this involves the "Buhlmann-Keller" weighted average formula for combining inert gas pressures and allowable values, into one value for creating ascent limits.

To see how this works, you need to get deep inside the dynamics of the formula involved.

***********

The above is intrinsic to all dive planning and use - we have all been using accelerated deco on virtually any deco gas switch. It can't be separated out with any tool we have at present, but easily done manually.

.

 

[wedivebc]

Back in the day ANDI used to teach washout ratios for various nitrox mixes. Using washout table you could use US Navy table for basic air deco then accelerate the deco based on the washout ratio of your deco gas. This table may still be found in the "Technical Safeair Diver Manual" from ANDI.

 

[hanymamdouh]

Thanks so much Mr. Ross for your reply.

In the ZHL / VPM gas kinetic formula, this involves the "Buhlmann-Keller" weighted average formula for combining inert gas pressures and allowable values, into one value for creating ascent limits.

do you mean the following formula (Schreiner equation)

Pt(t) = Palv,o + R ( t - R/k) - (Palv,o - Pt,o - R/K)e^(-kt)

 

[rossh]

Hi,

No, not Schreiner.

I guess we need to define what is meant by "accelerated" deco. In a one inert gas plan, any change in the N2/O2 ratio is straight forward and easily understood for what happens. While this speeds up deco, it all occurs directly proportional to the inspired N2/O2.

But a two inert gas plan, has to balance the limits of N2/He/O2, and making a change in the ratios here, can give rise to real accelerated deco. The model has to bring two sets of inert limits, into one limit for the diver to follow, and its here that the accelerated part occurs.

.

 

[hanymamdouh]

Hi,

I guess we need to define what is meant by "accelerated" deco. In a one inert gas plan, any change in the N2/O2 ratio is straight forward and easily understood for what happens. While this speeds up deco, it all occurs directly proportional to the inspired N2/O2.

.

I'm sorry not to make my question clear. I'm concerned with 1 inert gas only (N2/O2). That's why I mentioned Schreiner eq. In fact, I think of using Buhlmann's algorithm eq

Pcomp = Pbegin + (Pgas - Pbegin) x (1 - 2^{-te/tht})

this will allow me to calculate inert gas pressure (in my case PN2) at any depth after any period of time. Then plotting these values for all compartments on M-Value graph to draw a dive plan. From this point I can decide which phase I can switch to richer mixter (Lower N2) and recalculate for Pcomp as this equation work for on/of gassing rate, hence define the accelerated deco.

After delving deep into the topic, I concluded that it is impossible to work this on paper accurately, but it gave me a great understanding of how things occur and how software like yours work. And at least I can estimate values in case of any emergency and conduct near to safe ascend.

Being computer programmer; I can understand the huge efforts you put into v-planner and MultiDeco softwares, and I really appreciate your work.

 

[Dan_P]

"There is no science behind it.

As Jarrod Jablonski explained its origins to me when I was trying to come to an understanding of the difference between RD for GUE and UTD, RD was designed as a way to approximate what DecoPlanner would have come up with for that dive. If you plan dives with any software program and then plan some contingencies for those dives, it won't be long before you get the sense of a pattern. You can pretty much predict what the contingencies will be, within a certain range. So they made a mathematical process that creates an approximation of what DecoPlanner would give you for a certain range of depths using certain specific gases."

This is the sort of statement that makes me encourage interested people to seek knowledge from instructors actually qualified to teach the relevant subject.

 

[boulderjohn]

"There is no science behind it.

As Jarrod Jablonski explained its origins to me when I was trying to come to an understanding of the difference between RD for GUE and UTD, RD was designed as a way to approximate what DecoPlanner would have come up with for that dive. If you plan dives with any software program and then plan some contingencies for those dives, it won't be long before you get the sense of a pattern. You can pretty much predict what the contingencies will be, within a certain range. So they made a mathematical process that creates an approximation of what DecoPlanner would give you for a certain range of depths using certain specific gases."

This is the sort of statement that makes me encourage interested people to seek knowledge from instructors actually qualified to teach the relevant subject.

That's why I went to Jarrod Jablonski for that information--or doesn't he count?