Some Guy wrote:
Tom Horne wrote:

Is there any difference between a tank of welding oxygen vs
medical oxygen (...)

....


From what I've been reading tonight, ALL forms of compressed oxygen
(Aviation, Medical, Welding) come from the SAME source (a tank of Liquid
Oxygen - LOX) and are transfered to variously labelled tanks and charged
various prices based on the label on the tank.
....

So the bottom line is that if you walk into a welding supply store to
buy an oxygen tank, don't let on that you intend to use it to fill your
plane's on-board tank, or you want to make an oxygen tent for your sick
pet. ...

The bottom line is how confident do you want to be that what comes out
of that refilled tank is, indeed, fit for breathing purposes and hasn't
been contaminated since that point?

The scenario in the posting link later of a single large bottle
refilling known smaller ones is reasonably well controlled; just taking
the next random welding bottle returned from who knows where...errr, not
so much. As someone else pointed out, you don't know what was done with
those bottles previously nor what has been done since w/o the
certification--that's the role it plays.

As for cost; it's a lot like the "N-stamp" nuclear-grade
components--many of them are, in fact, identical to their non-graded
cousins but they've been through the qualifications to prove their
pedigree; the poor red-headed stepchild _may_ be just as good but
doesn't have the papers to prove it.

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