Ed Pawlowski wrote:

I know how a medical tank was handled. I don't know anything about
a welding tank. The oxygen may be pure going in, but I don't know
what was in the tank beforehand.

So you are speculating that the average compressed-gas retailer or
supplier does not perform the same steps to evacuate / clean / what-ever
/ a welding tank that he (or you) does with a medical tank.

I'm not stuck on decades information, my son owns a medical supply
company that supplies oxygen.

So you have a vested interest to maintain the impression that the
average citizen shouldn't or can't use less expensive welding oxygen
tanks in place of "medical" certified tanks for breathing or as a
respiratory aid.