Re: [PSUBS-MAILIST] O2

["Sean T. Stevenson"<sts@telus.net>]

Not quite.  The medical grade is, as you mention, tracked with an extensive
paper trail, which is why it is so expensive.  Prescriptions are necessary
if you are ordering it as medical grade O2 or filling medical cylinders with
the suppliers knowledge.  A better way to go is merely to specify the minimum
requirements of your oxygen (hydrocarbons, moisture content, etc.)  If the
medical stuff fits the bill, they will supply that with no prescription.

The aviator grade is of the same purity.  The difference there lies in the
tested and certified moisture content of the gas.  Aviator grade oxygen is
extremely dry (the idea being to avoid any problem with moisture freezing due
to adiabatic cooling at altitude).

The welding stuff is exactly the same (filled from the same cryo tanks as every
other grade), with the sole difference that it is not tested, certified or
otherwise tracked apart from the supposed content.  Even these cylinders are
vacuumed once prior to filling - and they are pure enough to breath (unofficially,
of course).  Common sense applies, and you should always analyze the contents
of a cylinder to discover gross errors (such as correct valve - wrong gas).


Get yourself a copy of Vance Harlow's "Oxygen Hacker's Companion" - a handy
reference for dealing with gases and gas suppliers.

-Sean

>As far as I know, oxygen is divided into 3 major groups:
>
>1. Medical
>2. Aviation
>3. Welding
>
>To get medical grade O2, you DO have to have a prescription. Now, in case

>with aviation grade as far as I know it's the same purity as medical. The

>difference is that you don't need a prescription to get it; and a tank, 
>unlike in case with medical grade, does not have a unique serial number each

>individual cylinder can be traced by, only the lot number. I think they're

>doing it in case of medical grade because life and death depend on it — they

>need a way to find out where the stuff came from if something goes badly 

>wrong.
>
>Medical and aviation O2 cylinders are getting purged of all gases before 

>they're filled with gas. Welding grade O2 cylinders are not. There's no 
>telling what could be in it other than O2. For all you know, it could be CO

>or some other pretty nasty stuff.
>
>However, welding O2 manufacturers say it's critical to have very pure O2 for

>metal cutting purposes, so I guess that stuff should be more than fit to 

>breathe.
>
>I'd try my chances trying to get aviation grade first. And then, if I 
>failed, I would talk directly to the manufacturer of welding grade O2 and

>ask him about chemical contents of his product.
>
>Sincerely, Paul.
>
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