David Strike wrote:

> Wouldn't you feel more comfortable with equipment that's O2 cleaned and
> serviced and where you didn't have to concern yourself with only having
the
> cylinders filled, for example, from a membrane system?

The obvious answer is yes, but it's not that easy.  I have 2 O2 cleaned and
certified tanks which I use for partial pressure fills from 40 to 22%
(acually, I think 26 is the lowest I've gone with them).  They can be filled
with air, but only from a nitrox quality source.  These tanks are, in fact,
the ones I use for nitrox most often.

On the other hand, there are reasons for having air tanks as well.  Jayna is
not nitrox certified.  She dives air and, when I dive with her, so do I.
There's no point in spending two to three times the money for a nitrox fill
when you know you're going to dive by air rules.  I have 4 non not O2
cleaned air tanks for this purpose.  There are a few reasons why these tanks
are not cleaned.  O2 cleaning and certifications are required annually and
they are not cheap.  I could do them myself, but would then have to come up
with some kind of industry acceptable sticker indicating that I had.  Since
tanks have to be inspected annually anyway, it's not worth my time.  Once a
tank is cleaned, it's important to ensure that nothing less than nitrox
quality air goes into it.  One fill from  contaminated source, and I get to
start over . . . if I'm lucky or more precisely, if the fill station
operator is lucky.  Not all shops do nitrox fills and some that don't, can
not meet the higher quality standards required for an O2 service tank.  So,
it's a good idea for me to have tanks that I did not pay to have cleaned and
don't have to worry about whether they are filled from normal versus nitrox
sources.  Keep in mind, that normal air is subject to standards as well and
that air tanks are also visually and eddie current tested annually.  We're
not talking clean versus dirty here, we're talking clean versus cleaner.

The obvious next question becomes, why would I ever use my air tanks for
nitrox.  That's easier to answer.  There are at least two situations where I
use my air tanks for nitrox.  Of course I only do this from a premix
(includes anything that does nto involve pure oxygen in my tank) source.
Most often, I use my air tanks because my O2 clean tanks are full of
something less appropriate for the dive, an oxygen concentration either too
high or two low.  I've been known to use gas from 26 to 39% on occasion.
For most of the dives I do in the Boynton area, 39% is too high and 26% is
too low, so I use get a fill in whatever tank is most empty or, if all are
full, one that costs me the least to drain, ie, one filled with air.  The
other situation where I use my air tanks for nitrox started this thread.
I've got as many as 6 Cozumel friends coming into town to go diving.  Most
of them will fly in.  The more I can loan tanks to, the more save money on
rentals.  It's likely that all 6 of my tanks plus any I can borrow will be
in use for nitrox for Boynton diving.  Since my tanks are safe for nitrox
use and fills in Boynton Beach are from a premixed source, there's good
reason to use them and little reason not to.

Lee