Discussion about EAD & END terminology

Dirk Hohndel dirk at hohndel.org
Tue Dec 10 05:29:48 UTC 2013

On Tue, 2013-12-10 at 08:51 +0100, Henrik Brautaset Aronsen wrote:
> On Tue, Dec 10, 2013 at 12:15 AM, Salvador Cuñat
> <salvador.cunat at gmail.com> wrote:
>         Attached is a simple patch that will do the work. No changes
>         on strings
>         and tried on EAN and TRIMIX test dives.
>         Would need a test run with CCR dives but it's far beyond my
>         posibilities, and I expect it would work well.
> I'm not able to test until tonight but something looks wrong with this
> patch.  
> 1) "EAD --> Equivalent Air Depth, considering N2 and He if diving
> trimix"
> This is just wrong.  You are talking about Helium and Trimix in the
> context of EAD, which is weird.  EAD is mainly used to show the depth
> as if you where diving on air, when doing Nitrox dives.  That way I
> can use Air tables when diving with Nitrox.
> 2) "Equivalent Narcotic Depth, considering both N2 and O2 narcotics."
> The description is better, but the calculation looks off somehow.  The
> role of END is to take into account the narcotic content of the gas,
> when doing Trimix dives: (pO2 + pN2) == (1 - pHe).  It is used to show
> how narcotic my trimix gas at a given depth is, compared to when
> diving on air.  If you look at my previous calculation:
>    The END (Equivalent Narcotic Depth) at 57 meters is (1 - fHe) x ATA
> = (1 - 0.45) x 6.7 = 3.7 ATA = 27 meters
> That means that when diving with 18/45 to 57 meters, I will not get
> more narked than if I was diving with air to 27 meters.  Good stuff.

Salvador, Henrik... can you work this out and send a patch authored by
one of you and ACKed by the other? I really would like to get this right
BEFORE shipping 4.0 :-)


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