NFPA 72 code sections · Emergency Communication Systems
Mass notification can override the fire alarm — if the risk analysis says so
An emergency communications system is designed from a documented risk analysis that identifies the threats (fire, weather, active shooter, chemical release) and how occupants should be told about each. The default is that the fire alarm signal has priority, but the code allows an in-building mass notification message to take priority over the fire alarm — for example to hold people in place during a security event — when the risk analysis supports it and the AHJ approves. Any such override has to be recorded, the fire alarm must resume once the MNS message is done, and the panel has to show the fire alarm was suppressed.
NFPA 72 reference
Chapter 24 — Emergency Communications Systems
24.3.12 Risk Analysis for Mass Notification Systems; 24.4.3 In-Building Mass Notification Systems (MNS priority over fire alarm signals where permitted by the risk analysis and AHJ; fire alarm resumes after the MNS message and the override is indicated at the control unit)
References use NFPA 72 2019/2022 numbering — section numbers can shift between editions, so confirm in the edition your AHJ has adopted.
On the job
A university lecture hall gets a combined fire/MNS system. During commissioning the integrator leaves the MNS at default priority, so a test weather message is cut off the moment a smoke detector is tested. The campus risk analysis actually calls for lockdown messages to override fire evacuation; the priorities are reprogrammed per the approved document and the AHJ witnesses the retest.
Quick check
1. The starting document for designing a mass notification system is the:
2. An MNS message may take priority over the fire alarm when:
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