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Devon E Bowen wrote:
> 
> Somebody (no attribution) wrote:
> > 
> > One item you wrote that interested me was the fact that you'd adjust 
> > for the altitude. Exactly how would you do that?
> 
> What I was suggesting was adjusting the tables as you would for any
> altitude dive. [Adjust for 8000' (cabin pressure)...]

Am I missing something?  In adjusting your tables, you're assuming that 
you have been at 8000' long enough to have outgassed N2 accumulated at 
whatever (lower) altitude you came from and are at equilibrium at 8000'.
All the tables (and computers) I'm aware of assume that you start at N2
equilibrium.

In the example you give, you are diving at sea level.  By adjusting your 
table for 8000' you are ignoring the fact that your tissues are already 
saturated at a higher pressure of 1 ATA.  All you table calculations will 
be off because this initial N2 load is not accounted for.

Now, if you dive for 24 hours (or whatever 3x the longest compartment 
half-time in your particular table is) this initial error will have 
dissipated away, and what you propose would be valid, but of course it 
would be wildly conservative for the remaining dives, since you only 
"surface" at 8000' after the last dive. 

> it seems reasonable to me that some day you may be able
> to tell your computer that you plan, for example, to fly in 6 hours.
> Then just let the computer adjust your dive time to make it safe.
> 
> Devon

All the computer needs to do is, after you complete a dive, continue to 
calculate the safe ceiling, where in this case ceiling is above sea 
level, so it needs to have a table to convert pressures in FSW to alti-
tudes.  It will be safe to fly, under your assumption, when you ceiling 
reaches 8000'.  Full decompression computers should allow you to plan 
this in dive planning mode.

I thought some computers did this calculation today (don't know what 
ones) while most just implement a 12- or 24-hour count down upon 
surfacing.

Cheers!

Brad May (bmay@co*.ci*.co*) 

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