Remember that the spec's for the different grades were originally set
as levels of minimum purity, not maximum purity and not even typical
purity**.  At that time dirty was cheaper so there were differences.
Today all grades are made using the highest volume production method,
yielding one grade that passes all minimum criteria.  So we are free to
breath clean and pure O2 whatever the label. And cheaper is indeed
better!

Robert M. Simon
ES-P N301ES

**  Reminds me of the story wherein General Motors told a potential
supplier in Japan that they expected 99.99% adherence to the
specification.  The Japanese company, being eager to please, agreed but
noted that they would have to set up a special production run to make
that 0.01% out of spec to meet GM's requirements.  
 
________________________________

From: Byron and Jean Buckingham [mailto:byronjean@jefnet.com]


But, don't do it, welder's oxygen contains too much water, and
other impurities.  It will freeze at high altitudes, more importantly it
can corrode the regulator and gauge and will void any warranty.