The building code mandates the required fire resistance rating of a wall in a particular location, and also states the required rating of the opening protective, or fire door assembly. The fire resistance requirements for various types of fire walls, fire barriers, and fire partitions, as well as smoke partitions and smoke barriers can be found in Chapter 7 of IBC.
The 2012 edition of the International Building Code includes new tables that help clarify the opening protective requirements. For example, Table 716.5 states a two-hour exit enclosure requires a 1 ½-hour fire door assembly, and lists requirements for the glass used in that assembly. The rating of the door assembly is often less than the required rating of the wall, because it is assumed the door will have a lower fuel load since no combustibles (e.g. furniture, storage, etc.) will be piled in front of the door. If a fire door is no longer needed, it should be removed and replaced with construction of the same rating as the wall to accommodate the potentially higher fuel load.