If the primary power is disconnected and the fire alarm system goes into an alarm condition, what is the minimum acceptable time for secondary power to operate the voice evacuation systems?

For voice evacuation systems in a fire alarm system, the minimum acceptable time for secondary power to operate is critical to ensure that occupants can be effectively notified and evacuated in the event of an emergency, especially if primary power is lost. A duration of 15 minutes is considered sufficient to allow for adequate alarm coverage, ensuring that messages can be communicated effectively throughout the building.

This period allows the system to function long enough to provide instructions for evacuation, inform occupants of the situation, and give them time to respond appropriately. Additionally, standards and codes governing fire alarm systems, such as NFPA 72, often specify this 15-minute duration as a requirement for secondary power for voice communication systems to support occupant safety.

Shorter durations may not provide enough time for occupants to react and evacuate, and longer durations could imply unnecessary complexity or redundancy not typically required in standard operational scenarios. Thus, 15 minutes strikes a balance between operational efficiency and safety requirements.