What minimum backup battery capacity duration is required to sound the fire alarms?

• A. Ten minutes
• B. Five minutes
• C. One minute
• D. Fifteen minutes

Answer: (B)

The requirement focuses on how long the backup power must keep the alarms sounding after a power loss. The idea is to ensure occupants have a reasonable window to hear the audible alerts and begin evacuating, even if the main power goes out. Five minutes is the minimum duration that meets this practical need—long enough for alert transmission and initial evacuation, but not so long as to require a much larger backup system. A one-minute duration wouldn’t reliably support evacuation, while ten or fifteen minutes go beyond the minimum standard. So, five minutes is the shortest backup-power time that satisfies the requirement.