Art you wrote ...... 

>

>Say you are using a helium rich mixture, say 50% He, 21% O2 (want to
keep

>the O2 the same when comparing.  What you would be doing with this mix
in

>your tanks I don't know.

>


There are a number of reasons you might have this mix in your tanks but
the most common reason would be the site you set out for today got blown
out and you ended up on a shallower wreck.


Back in November of '92 we all went out with sets of 17/50 trimix for a
dive on the <italic>U-Who </italic>only to wake up in the middle of
snotty seas and opted not to continue out to that wreck. We were already
committed to the day for diving and opted to go to the USS San Diego for
some fun dives, but with only one set of  air on board (yeah we used to
use air for 65-120 fsw dives).  Via Cell Phone Billy Deans got Dr.
Hamilton to make us tables to use that mix that day on a 120 fsw site.
Mind you this was long before desktop software. 


The point is there will come a time when the "perfect mix" is not
available and you need to make due with what you have.  Although 21/50 is
not an optimal gas for a 130 fsw dive site it does have some merits. A
PO2 of 1.01 atm and P-air of 3.55 atm.  The clarity at 130 fsw is about
50 fsw/air which means lots of fun looking for artifacts. 


The 21% oxygen makes the deco time quite reasonable (vs 16%) whereby you
can do anywhere between a 20-60 minute dive with no more than 15-60
minutes of deco with the OEA50%. (run on Abyss. Add in 100% oxygen and it
drops to almost a range of 10-50 minutes respectively. 


For the most part once the oxygen is introduced the decompression time
starts to drop quickly, and missing a few minutes either way rarely makes
a whole lot of difference (don't read that to mean you can cut your time
bend-free).


As George has indicated he has had good experience experimenting and
testing decompression models and profiles on himself. We all do that to
some extent each time we dive. The empirical data that gets accumulated
while one works a set of tables is invaluable to the ultimate
decompression profile. 


For the most part I have used either Hamilton Research Trimix Tables or
Abyss software for eight years now, with some very good results. The key
is to keeping good notes, and understanding how the model works with you.
Where I cut some time and add some other, that may not work for you or
someone else, but it does for me.


As long as you accept the fact that DCI is not an accident, that it can
occur on most any dive where decompression is incomplete (incomplete for
the gas load not necessarily completing the table in hand,) then you can
mess with this stuff all day long. The proof is in the diving. I just
would caution those who are new to decompression diving that a 60 or 100
minute deco is not a walk in the park, especially in the ocean. It's easy
to toss around long or short deco times from the comfort of  the boat
deck, but when the sea kicks up, shorten the bottom time and get the
flock out of the water. 


All decompression tables work until they don't


Regards, 




<bold>Joel D. Silverstein

</bold>http://www.trimixdiver.com

http://www.nitroxdiver.com

--------------------------

Technical Diving Resources

--------------------------
--
Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'.
Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.

Navigate by Author: [Previous] [Next] [Author Search Index]
Navigate by Subject: [Previous] [Next] [Subject Search Index]

[Send Reply] [Send Message with New Topic]

[Search Selection] [Mailing List Home] [Home]