See the 1999 NEC, Section 700-1, FPN No. 3:
Emergency systems are generally installed in places of assembly where artificial illumination is required for safe exiting and for panic control in buildings subject to occupancy by large numbers of persons, such as hotels, theaters, sports arenas, health care facilities, and similar institutions.
Emergency systems may also provide power for such functions as ventilation where essential to maintain life, "fire detection and alarm systems," elevators, fire pumps, public safety communications systems, industrial processes where current interruption would produce serious life safety or health hazards, and similar functions.
