Reference · Design
A-weighted Decibel (dBA)
Sound level measured with the A-weighting curve, which approximates human hearing. Public mode audible signals must be at least 15 dBA above average ambient or 5 dBA above the maximum 60-second sound level, whichever is greater.
NFPA 72: 18.4.4 (Public Mode Audible Requirements)
Section numbers vary by edition — confirm in the edition your AHJ has adopted.