One-hour (60 minute) doors
One-hour rated doors are used in walls between rooms, which are also typically one-hour rated.
3/4-hour (45 minute) doors
Doors with 3/4-hour fire protection rating are used in one-hour walls. A 3/4-hour rated door is found in walls of corridors and room partitions. A door with this rating may also be located in the exterior wall of a building subject to moderate fire exposure from the outside of the building.