the stuff of life....
for FLs air survey bottles our were filled with "medical dry breathing oxygen".
You needed then, if to DIY to have the connectors and gauge units to do the refill. ...and keep everything meticulously clean....and free from any oil contamination. Or else !!!!
I have never heard of low pressure making things toxic
Bottles do need regular check ups for corrosion, servicability etc.
Breath easy !
ps arent scuba bottle refilled with just air??