No decompression limit equation question

[wstorms]

If you have empirical data showing that ZH-16C at GF70..85 is "too aggressive" (Freadrich), and/or that longer ascent times result in "better" DCS scores (Spisni), you should publish it in a peer-reviewed journal.

Otherwise, I wouldn't.

Keep in mind the C version (actually the B already) was developed to add more conservatism compared to the original Buhlmann M values and the ZHL16 algorithm
Adding GF is a way to add conservatism on top of that. If that was already added I must have missed it, and in that case I agree you are probably good to go.
I read the OPs statement as a reference to the original M values, without GF. Could be wrong there.

 

[John C. Ratliff]

If you go to the current U.S. Navy Diving Manual, they recommend that, for Navy divers using commercial dive computers, that they validate the computer against the U.S. Navy Dive Computer, and have aprotocol for that. You might check it out before trying to actually use your calculations for a dive.

SeaRat

 

[theofficialcroissant]

Looking for some help on a personally build pet project of an excel VBA based dive computer:

The project is just for fun, and to understand the black box that is a dive computer. I have almost everything working, but am running into one issue that has been stumping me for several days. My VBA code is a Euler time step model (calculate current state of tissues, hold constant for a small time step, update values, etc etc). Everything works properly except the running NDL calculation during an ascent. I'm calculating NDL for a standard air dive as LND = halftime/0.69*ln(1-()ppn2_allowed_at_surface-ppn2_current_in_tissue_compartment)/(ppn2_in_tissue_compartment)-ppn2_inspirated)). I'm pretty confident this is correct, can provide more details on what it means / the derivation if the formula looks weird.

Anyway my issue is that during ascent phases I generate a negative ln which of course is undefined. I took a quick look through the code by dmazuik, and I think it avoids this issue by not updating tissue partial pressures during ascent. I'd like to do this as my code is not just discrete steps at different depths, but allows you to ramp from one depth to another.

Any help is much appreciated and ill of course give you credit for the assist if I make the program available to more people

Best,

 

[LFMarm]

If you have empirical data showing that ZH-16C at GF70..85 is "too aggressive" (Freadrich), and/or that longer ascent times result in "better" DCS scores (Spisni), you should publish it in a peer-reviewed journal.

Otherwise, I wouldn't.

The work on iso risk curves by NEDU and led by Doolette shows that for bigger dives (higher PrT), the length of deco needs to be higher (ie lower GF High) to keep risk of decompression sickness equal.

Question - Iso-risk decompression schedules

I just watched the great presentation of David Doolette at RB4 on alternative decompression strategies (Advances In Decompression Theory And Practice). He shows a Navy algorithm that provides decompression schedules that are iso-risk. Interestingly they are similar to GF 50/85 for shallower...

scubaboard.com

From those curves, it seems that for NDL dives a GF High of 80 has a risk of DCS of 2.3% or less; for saturation dives the same risk is achieved with GF High of 40.