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To meet the 15 dBA requirement, there are cases where high levels of background noise require
extremely high levels of emergency annunciation to overcome the noise. When background noise
exceeds 105 dBA or when the SPL calculations require greater than 110 dBA, the use of visual
notification appliances is warranted.
There are cases where the background noise can be reduced or eliminated by allowing the
emergency voice/alarm communications system to remove the source of the noise. For example,
background music can be disabled during an alarm condition.
Very large areas such as arenas pose a particular challenge to meeting NFPA 72 requirements.
These areas have sound systems installed that produce tens of thousands watts of power, however
these systems are not typically designed to meet NFPA 72 requirements. If the systems are
engineered to provide adequate SPL and intelligibility then it would make sense from a
performance perspective to use the systems for emergency evacuation. By working closely with
the AHJ and the building’s owner, it may be possible to allow the use of the existing PA system.
However, some modifications may be required.
Audibility, Continued
High Background
Noise
Large Areas