George wrote:

Next time watch the significant difference on how medical use vs
other tanks are filled. Any medical use tanks are first evacuated
to insure there is nothing else in the tank before it is filled.

How exactly could something get into the tank in the first place?

If it's connected to a manifold system, then yes, the gas from a
higher-pressure tank could flow into it. But doesn't that
higher-pressure tank already contain known-pure O2?

If it's never connected to a manifold system or to another tank, then
how exactly could something get into it? Deliberate tampering?