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Art Greenberg wrote:
 
> Cylinders and valves should be cleaned *and filled only with clean gas* if
> you ever expect to introduce pure oxygen at high pressure into them.
 
Some shops, including the one in which I received my training, do nitrox
fills by first introducing pure oxygen and then completing the mix with an
appropriate volume of air, hence the need for a cleaned tank.
 
>There is no reason to limit a clean cylinder to nitrox use - EAN21 is fine,
as
> long as the source meets the appropriate standards for hydrocarbon
> content.
 
The logic here is clear, but begs a question by the uninformed.  What are
the standards and how does one know they are being observed?
 
> Even a few fills of Grade E (the minimum CGA grade for SCUBA
> applications) in a season would be ok, as that's "pretty clean" - it would
> take a number of borderline Grade E fills to add enough hydrocarbon to
> cause concern.
 
This does not seem like something I would be comfortable with.  Again, as
the uninformed, I would chose to avoid a risk which I don't fully understand
when the possible result of a mistake could be catastrophic.
 
> Some O-ring and diaphragm materials will break down over time in the
> presence of high pressure oxygen. This is a cumulative effect. It has not
> been an issue in my diving over the last three seasons. My "standard"
> regulators have showed no sign of problems this season after 120 or so
> hours of exposure to EAN28.
 
> > Since I have no plans to dive percentages greater than 40% in the near
> > future, my short term plan is to have my regulators O2 cleaned at their
next
> > service interval and use them for whatever diving I happen to be doing.
 
> This will certainly do no harm, but may be a waste of money. If you're
> going to be this conservative, you should then *not* use your regulators
> with standard air.
 
The basis for my decision to have the regulators oxygen cleaned is primarily
based on a preference to avoid the cumulative damage to materials not oxygen
compatable.  As far as I know, the one time cost of replacing incompatable
parts is relatively small relative to the benefit of reducing the
probability of regulator failure when I least want a failure, on an
expensive dive vacation for example.  At my present risk tolerance level,
I've bought in to the concept of compatable materials and the idea that,
having done so, use of EAN21 - 40 is OK.  Limiting my regulators to EAN use
is undesirable.  I have 4 regulators for 2 people, the extra regulators
resulted from upgrades to what we like best.  They're fine as backups but
not our preferred equipment.
 
Lee