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If you are diving with individuals who have a significant difference in SAC rate
*and* you are encountering a wide variety of cylinder types/volumes, what is
wrong
with a bit of conservatism? With a degree of variance in each cylinder's actual
volume (not posted specs), pressure gauge accuracy between divers, RMV at rest,
normal, and stressed, not to mentioned reg/isolator shut down time if a failure
occurs, on and on, conservatism in gas management is something you should
certainly have allocated. Too many variables and the potential accumulation of
those variables are ever present to be attempting an exact gas management
calculation. In fact, under actual field conditions, it cannot be done.
I believe the IANTD tables were meant to be used as a guide. Modifications
can be made by the diver(s) as deemed necessary. Also, exact SRF's would
necessitate a table big enough to make a rain suit. Hell, I think I'll pass that
on to Tom.
Gas management is probably *not* an area of the dive plan where a person
should be bitching about 1/10 of a cubic foot. Be conservative. A day might
come when you are glad you were.
-Jason
P.S. If you want a hypothetically exact calculation formula, I'll send it to
you, but it sounds like you've done something like this already.
Imdamaged wrote:
> I recently found this tech diver list. Man you guys are mean!!!! All this
> talk is about diving ? There MUST be a WOMEN involved somewhere to generate
> this type of animosity. ANYWAY..
>
> My post is about Gas matching as presented in the IANTD Deep Air Text. The
> book describes a method of calculating the required adjustment to the rule of
> thirds for a penetration dive for a pair of two divers. The IANTD solution
> involves working through a series of tables to determine the "turn pressures"
> for the divers.
>
> I attempted to verify and regenerate the tables using a spreadsheet and found
> that the solution presented by IANTD in the Deep Air Text is not correct.
>
> The error in the solution is that sometimes the answer is correct and
> sometimes it is around 15% conservative depending on the relative tank volumes
> and RMV's of the individual divers. The diver using the IANTD tables seems to
> have no way of determining when the solution is exact (i.e. no magin for
> error) and when it is conservative.
>
> I have written a simple spreadsheet solution to get the answer correct. It
> would seem that a diver using this technique could add a known safety factor
> rather than an unknown or non-existant one as is supplied by IANTD.
>
> I have provided documentation of the problem to Tom Mount and IANTD quite a
> while ago and have received no response.
>
> Does anyone really use the IANTD method? Does anyone want to do it correctly
> with a spreadsheet? Is this just petty BS that the experts know about
> already?
>
> Jim Fyfe
>
> Jim Fyfe
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