Emergency Voice/Alarm Communications Systems
Chapter 24 of NFPA 72 addresses emergency communications systems (ECS), which go beyond traditional fire alarm notification by providing voice and data communications during emergencies. Emergency voice/alarm communications systems (EVACS) use speakers to deliver live or pre-recorded voice messages to building occupants. These systems allow targeted messaging to specific zones, enabling phased evacuation strategies and providing real-time instructions during evolving emergency situations.
Mass Notification Systems
Mass notification systems (MNS) represent a broader category of emergency communications designed to address threats beyond fire, including severe weather, active threats, chemical releases, and other hazards. MNS may be configured as in-building systems, wide-area systems, or distributed recipient systems. In-building MNS use speakers and visible appliances within a building. Wide-area MNS use high-power speakers, sirens, or other means to reach outdoor populations. Distributed recipient MNS deliver messages via telephone, text, email, or other personal communication methods.
Intelligibility and Performance
A central requirement of Chapter 24 is speech intelligibility. Voice messages must be clearly understood by occupants in all areas served by the system. The code requires that designers measure or calculate intelligibility using recognized metrics such as the speech transmission index (STI). Factors affecting intelligibility include speaker placement, room acoustics, ambient noise levels, and system equalization. Design documentation must demonstrate that intelligibility requirements will be met.
Two-Way Emergency Communications
Chapter 24 also covers two-way emergency communications systems, including area of refuge communication stations and firefighter telephone systems. These systems enable communication between building occupants in areas of refuge or stairways and a central control point. Two-way radio enhancement systems for in-building fire department communications are also addressed, ensuring that emergency responders can maintain reliable radio communication throughout the building.
