So there are actual rules and regulations with fill pressures and oxygen mixtures in cylinders.
However, the shop has there facts mixed up a little.
DOT 3AL type cylinders are limited to a fill pressure of 3000 PSI for oxygen service. And "oxygen service" is any gas that contains more then 23.5% oxygen. To put any gas in a cylinder that has more then 23.5% oxygen in it, the cylinder and valve must be O2 cleaned, it must have straight threads, and the valve must be brass or stainless.
There are no pressure limits listed for an oxygen mixture for any of the 3AA cylinders. And worthington's special permit required to make the HP cylinders does not list a pressure limit as well. The cylinders standard fill pressure limit still applies of course.
Here is a link to the DOT regulations regarding this issue, its CFR 49 section 173.302 paragraph (b) sub paragraph (4)
Electronic Code of Federal Regulations:
Here is a link to the special permit filed for Worthington cylinders SP14157
http://www.phmsa.dot.gov/staticfiles/PHMSA/SPA_App/OfferDocuments/SP14157_2009070249.pdf
Looks like Mike beat me to it, nice post Mike. I posted the actual links to the actual laws that are current and up to date as of this posting for the na sayer's that will now jump out of the wood work.
