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Reference · Design

Intelligibility

How clearly voice messages can be understood, measured with STI/CIS. Voice systems must be intelligible in acoustically distinguishable spaces, not merely loud.

NFPA 72: 18.4.11, Annex D

Section numbers vary by edition — confirm in the edition your AHJ has adopted.

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Read more in these guides

Voice Evacuation Intelligibility, Explained (NFPA 72 Chapter 24)A voice message no one can understand is worse than a tone. Here's how Chapter 24 turns 'clear enough to act on' into something you can design and measure.

Related terms

Candela (cd)A-weighted Decibel (dBA)Manual Fire Alarm Box (Pull Station)Secondary Power SupplyStandby (Supervisory) CurrentAlarm Current
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