What is the industry requirement for clearance around a steel door in a steel frame?

Where doors have been fire-rated, such clearances are subject to regulation under NFPA 80, “Fire Doors & Other Opening Protectives”. The clearance between the door and frame must occupy a space of at most 1/8″. Clearances between the adjacent edges of two doors must be 3/16″. Clearance from the lowest point of the door to the lowest point of the frame must not exceed 3/4″. Clearance between the door face and the stop must be 1/16″.

SDI 100 A250.8-2.1.8 details more information on clearance.