different tissue definiton in OSTC and subsurface

Robert C. Helling helling at atdotde.de
Thu Jan 10 14:26:17 PST 2013

On Jan 10, 2013, at 8:37 PM, Jan Schubert wrote:


> I just stumbled over the fact that the OSTC seems to use different
> definitons for halftime, a and b for N2 and He for the fastest tissue
> (#1) then the definitions in subsurface. Some implementations for
> Bühlmann different between Tissue 1a and 1b, might be that this might be
> a reason, just a guess.


> Anyway, changig the values to the one used in
> the OSTC and also ignoring the precompiled values for 1sec

You realize those are used in the deco calculation, not the half-times? In any case, for a half-time t12 you can compute the precompiled value for one second as

1 - exp(-ln(2) / 60 / t12)

which should be well approximated by ln(2) 60 / t12 (the error being about the square of this number).

> I do not see
> much difference in the outcome of the calculated deco for my example (as
> in there most likely the slower tissues will lead). Attached is a diff
> for this.

> Also I've seen the OSTC defining more conservative values for
> satmult=0.9 (instead of 1.0) and desatmult=1.1 (1.01) which will result
> in much more conservative calculations then we see now so this might
> something which I may got wrong.

I would have though that results in more aggressive profiles: It loads the tissues 10% at depth and clears them 10% faster.


Robert C. Helling     Elite Master Course Theoretical and Mathematical Physics  
                      Scientific Coordinator                                   
                      Ludwig Maximilians Universitaet Muenchen, Dept. Physik    
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