[PATCH] Fix deco planning for low oxygen mixes

Robert C. Helling helling at atdotde.de
Tue Jan 8 13:49:40 PST 2013


On Jan 8, 2013, at 8:59 PM, Jan Schubert wrote:

>> BTW: weren't you one of the people who despise the 3m stop at the end?
>> Or was that someone else?
> 
> Hm, I'm just saying that there are people how do not 3m but 6m stops as
> the last stop. Personally I do 3m and would like to be able to do 2m or
> even 1m if my dive computer or dive planning software would allow this.
> Mind the pressure difference when surfacing from 6m (1,6bar to 1bar -
> 60%!) or 3m (still 30%) and compare this to a ascend from 90m to 80m
> (just 10%).

If you have 100%O2 as a deco gas you don't gain anymore a lower inert gas pressure for off-gasing by ascending from 6m to 3m. So you can do a large part of the deco there which might be more comfortable if there are significant waves or boat traffic or (for cave divers) you have a habitat there. For the reasons Jan mentioned you still want to follow this with a very slow ascent from 6m to the surface.

But this applies only for O2 deco. My experience with dives using only air and with some minutes of deco obligation is that at 6m it typically takes twice as long to finish deco than my Vyper/Vytec suggests it takes at 3m.

Best
Robert

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