Don Foreman wrote:

On Tue, 11 Jan 2011 17:33:23 -0600, Ignoramus29041
wrote:

can industrial welding oxygen be used to breathe. Long term effects
are of no importance whatsoever.

Long term effects may seem more important when the doc gives you the
bad news years later.

In many cases, welding oxy and medical oxy come off the same manifold.
Medical oxy has a high standard of purity but it's often not
cost-effective to maintain different fill manifolds. Oxygen is
produced by distillation of liquid air in either case but some
filtering is applied to medical oxygen. Unfiltered LOX is still quite
pure unless the plant producing it draws its air from near an LA
freeway or something. Even then, the distillation process would
purify.

The purity standard for welding O2 is higher than the purity standard
for medical O2. Only the analytical grade has a higher purity standard
and sees any additional testing.