Section 21.3.1/In-Building Mass Notification Systems
NFPA 72 Section 21.3 covers mass notification system design including speech intelligibility and priority over fire alarm.
In-building mass notification systems must provide intelligible voice communications to all occupied areas. The system must achieve a minimum speech intelligibility of 0.70 Common Intelligibility Scale (CIS) or 0.65 Speech Transmission Index (STI) in each space. The MNS must have priority over the fire alarm system and any background music or paging systems. Pre-recorded and live voice messages must be supported. The system must operate on emergency power with the same battery and generator requirements as the fire alarm system. Visual notification (text displays, visible signals) must supplement audible notification.
Why this section exists
Mass notification systems address threats beyond fire (active shooter, severe weather, hazardous material release, bomb threat) where occupants need specific instructions rather than just an alarm tone. During the September 11 attacks and subsequent mass casualty events, the inability to deliver intelligible voice instructions contributed to confusion and delayed evacuations. MNS requirements ensure buildings can communicate specific protective actions (evacuate, shelter in place, lockdown) to all occupants simultaneously.
What plan reviewers look for
Plan reviewers check the fire alarm drawings for MNS speaker locations and coverage. They verify the speech intelligibility calculations or testing specifications. They check that the MNS has priority over other audio systems. They verify emergency power provisions (battery and generator). They check for text display capabilities and integration with the fire alarm control unit.