you've never noticed that the connectors for co2 are different vs nitrogen vs oxygen, etc. etc? i'm not an authority or someone who's worked in the industry but its pretty obvious the containers are not interchangeable...
we had a bulk liquid tank we used at our old brewery and i remember that in the process of looking for supplier initially i asked them about food grade vs industrial. i was told that because we have a big old budweiser plant, crap ton of wineries, a large amount of hospitals/medical/research activity, and a major population center that food grade was the default. i've never even seen the option of selecting your grade at praxair, matheson, airgas, etc. we also have a few refineries as well which you would think would use alot of cheaper industrial grade. but i've never seen it offered. ( i also havent ever asked for it) but the story seems to match reality in our area.