Cheap compressors (even labeled oil free) will still have residue machine oil on internal surfaces from the manufacturing process. Chinese manufacturers usually

Cheap compressors (even labeled oil free) will still have residue machine oil on internal surfaces from the manufacturing process. Chinese manufacturers usually surface coat metal to prevent rusting during shipping. It might not be enough to bother you or I, but if someone is respiratory compromised to the point they are on a vent, they really need medical grade oxygen.