From: mayne@open.cs.fsu.edu (William Mayne)
Newsgroups: rec.scuba
Subject: Re: Oxygen Decompression
Date: 3 Apr 92 16:02:35 GMT
Article-I.D.: mailer.1992Apr3.110235.22518
Reply-To: mayne@cs.fsu.edu
Organization: Florida State University Dept. of Computer Science

In article <920402192121_73467.2574_DHE76-2@CompuServe.COM> 73467.2574@CompuServe.COM (Andy Schmidt) writes:
> 
>However, if decompression involves several hours, other procedure might
>apply.  You could decide to decompression on mixes other than air with an
>elevated O2 level at the 30 meter decompression stops and later switch to
>pure O2 for the 3 and 6 meter stops. At that point, hypothermia might be a
>major concern as well as O2 toxicity.
> 
>For such an application you can't just modify your standard air tables, you
>NEED custom tables with appropriate bailout/alternative options.  Custom
>tables will cost about $ 5.00 per depth/time combination.
> 
>I recommend Prof. Buehlmann's book 'Dekompression und
>Dekompressionskrankheit' published by Springer in German and English with
>complete dive table algorithms for any mix for O2, N2 and He.

I've read the English version of Prof. Buhlmann's book and I concur
in recommending it.

Since the algorithm and all the parameters for the Buhlmann model (and
several others) are published and any PC can be programmed to compute dive
tables from them $5.00 per depth/time combination seems like a rip off to me.
The vendors of custom dive tables claim to have specially tweaked trade
secret models. I won't say that this is just marketing hype. I actually
believe otherwise. But I don't see why a published model which has been
tested, subjected to review, and used to generate tables which have been
used by thousands of divers shouldn't be okay.

I haven't tried to adjust my decompressions based on my own calculations
because I haven't had the need to do it yet, and I may never. The longest
decompression I've ever done was 131 minutes, which is not so long that
I feel the need to risk adjustments. But I don't know any good arguments
against computing my own adjusted decompression schedule rather than
relying on someone else's. It would seem to me that if I have confidence
in my programming (which I do) I should be as willing to dive a table I
compute from a model as one somebody else computes from that model.

The only places I see room for tweaking are adjusting the parameters
to make the model more conservative (or less, but I don't even want
to think about that) and reducing repetitive dives to pressure
groups. The math for the former is very simple, and there is no need
to do a repetitive dive table with pressure groups. Even if repetive
dives are done it is better to compute the entire profile, including
surface intervals, for all compartments anyway. Such calculations can
be done with my own computer, better than any precomputed table. Hence
I might consider buying a program with one of these trade secret
models from an expert like Bill Hamilton, but not a $5.00 per line
table which can't possibly cover all profiles without a bunch of
fudge factors and approximations. 

Is anyone out there willing to admit if they have actually dove
home grown schedules? I would be most interested in your experiences
and comments.

Bill Mayne
From: davew@hp-ptp.ptp.hp.com (Dave Waller)
Date: Sun, 12 Apr 1992 15:16:43 GMT
Subject: Re: Scuba Lessons in Peekskill, NY
Organization: HP Pacific Technology Park - Sunnyvale, Ca.