Simon,

Oops...
My mistake: the formula should read: (fO2+fN2)*(D+33)-33

That qualifies a mix like 18/45 instead of 18/55 for this dive...

Regards,

THOMAS


----- Original Message -----
From: S I L E N T I M M E R S I O N <silent@cu*.ne*>
To: Simon Murray <simonm@ho*.co*.za*>; Tech Diver
<techdiver@aquanaut.com>
Sent: Monday, December 06, 1999 12:11 PM
Subject: Re: O2 Narcotic was Re: decompresion gas selection and procedures


> Simon,
>
> > I have been going through your post and I have a few questions regarding
> the
> > calculation of EAD (assuming O2 is narcotic).
> >
> > I assume that you meant your formula to read as follows: (FO2+FN2) /
> > .79(D+33)-33   and not FO2+FN2/.79(D+33)-33.  The difference being the
> extra
> > set of brackets.
>
> Of course, with brackets...
>
> > I  use the adjusted formula in the following example:
> > 61m (200ft) dive using 18/40, I get an EAD of 43.9m
> > 61m (200ft) dive using 18/55, I get an EAD of 30.4m
> >
> > and a 61m (200ft) dive using Nitrox 18 gives an EAD of 79.8m since the
> > formula adds fractions of O2 and N2.
> >
> > Now, if I run a similar dive on zplan (O2 set to narcotic), I get an EAD
> of
> > 37m, while GAP gives 32.5m.  Clearly different packages use different
> > formulas to calculate the narcotic effects of oxygen, with Thomas's
being
> > the most punitive on O2.
>
> It would be interesting to see all different ways to calculate the true
EAD
> for a trimix and evaluate which one is most valid. I just present the way
I
> do it and my assumption is that the higher He is better...
>
> Regards,
>
> THOMAS
>

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