On Thu, Jul 28, 2016 at 2:52 AM, Rick Walsh <[email protected]> wrote:
> > > On 25 July 2016 at 09:33, John Van Ostrand <[email protected]> wrote: > >> >> Although my Cochran offers very generous amounts of no-deco time the one >> conservative feature is its no-fly time. At the end of a week of >> live-aboard diving it often displays no-fly times well over 24 hours. >> >> I can only guess that it's offering desaturation time. The fact that in >> practice a 20 tissue model no-fly time is longer than the 16 tissue model >> also suggests it's a desautration level and the longer tissues of the 20 >> tissue model means longer desat times. >> >> >> > In the DAN Flying After Recreational Diving workshop proceedings, Mike > Cochran said that the Cochran dive computer calculates no-fly time as time > it takes for all tissues to reach ambient pressure (i.e. desaturate) then > add 12 hours. That sounds like a conservative approach and is no doubt why > your dive computer gives long no-fly times. > p82 (p83 of the pdf) > https://www.diversalertnetwork.org/files/FADWkshpBook_web.pdf > > He didn't say what they consider to constitute having reached ambient > pressure (x half lives or a maximum difference between tissue and ambient > partial pressure). > Thanks Rick. I don't know the half times of Cochran tissue compartments but if the longest is 635 minutes (same as Bühlmann) so a 6x half time would be 63.5 hours. It would have to be a tissue tension threshold. I used 6x in a comment because that duration is how long people consider a fully m-value supersaturated tissue takes to de-saturate. That's somewhere around 1.5% of the m-value and I presume that means that a one half m-value super-saturated tissue would take only 5x to de-saturate. -- John Van Ostrand At large on sabbatical
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