What you think about using https://wiki.openstreetmap.org/wiki/Tag:shop%3Dtrade ?

And tagging it shop=trade trade=oxygen_for_industrial_use ?

(I also have seen some shops selling bottles with "high-oxygen air" as miracle cures, this also makes possible to both classify it in detail if some program supports rare values and allows to broadly support for apps supporting shop=trade and it sounds like shop=trade fits here)