Not (legally) mandatory, but if you want a shop to fill it then they can
enforce whatever rules they like.  They could quite legitimately say that
they'll only fill cylinders that are painted flourescent pink - the problem
is that you can be 100% confident about the source of your fills, but they
might not be.  Of course the annual O2 cleaning really doesn't mean much
either, but from their point of view thats really the most they can ask, and
by following that means that if there are any problems then they're
following industry standards so they'd be pretty much protected if there was
an accident.

Other option would be to get O2 from BOC or someone and do your own fills,
although then you have the issue of getting full pressure, hiring the
cylinders, etc.  Depending on how much you use it may be more trouble than
it's worth.

David

Steve,

I'm a bit surprised that you aren't already aware of these regulations and
conditions.

Before you bought the RB, were you not already a nitrox qualified diver and
owned nitrox cylinders?

This is are exactly the same situation as for normal open circuit SCUBA
cylinders, where 100% O2 is filled into an empty cylinder and then diluted
with air or helium and air.

Apart from the obvious reasons for the annual O2 clean that being the
removal of any hydrocarbon build-up over the year and a general inspection
of the condition of the internal surface of the cylinder, there is another
good reason for this service.

It's quite obvious that a cylinder that is only ever filled with 100% O2 is
less likely to become contaminated with hydrocarbons or water, as could be
the case in a nitrox cylinder where contaminants can be introduced from a
faulty or badly maintained compressor; however the use of 100% O2 also has a
negative impact on the longevity of all the O rings and seals.

Butyl rubber as used for all the O rings (Viton is not now commonly used),
may well last 2.5 years in a cylinder with low %O2, but RAPIDLY become
brittle and their effectiveness as a seal is compromised when used for
extended periods exposed to high %O2.

The relatively small cost of a O2 clean is a small price for peace of mind.

BTW, if you do decide to get your own O2 and complete one of the gas blender
courses, as I have done, you will also then be qualified to perform your own
O2 cleaning.  If you then decide to do so you will need to invest in some
additional tools and equipment.  If you choose not to make the investment
then at least you will know what is involved.

Tony

It's pointless but they are just saying what they were told on the course.
You want them to be mindless rule followers when it comes to compressed gas
as you might be in the shop when somebody brings in the "years out of test"
tank that really isn't man enough for 232bar anymore. I have no wish to be
digging bits of tank out of my vitals just because nobody looked at the stamps.

I fill my own which makes things easy although most shops are getting more
relaxed about 'clean' stickers provided it was cleaned at the last hydro/vis
cycle.

That said I've been in shops for 'clean air' after a bit of car boot mixing
and they've insisted on measuring it. When it comes in at 18% we've had some
interesting discussions.

nigelH