According to NFPA 72, battery backup of a household fire alarm system must sustain the system after utility power is disconnected for how many hours?

• A. 24 hours under normal load, 4 minutes under alarm load
• B. 8 hours
• C. 12 hours
• D. 48 hours

Answer: (A)

NFPA 72 requires that a household fire alarm system have enough battery backup to continue operating after power is lost. The system must run for 24 hours under normal load, which means the continuous, everyday current draw of detectors and related components. It also must have enough reserve to sustain the alarm load for at least 4 minutes, since sounding devices draw more current during an alarm. This combination ensures long-term standby capability and a short, reliable window during an actual alarm for occupants to evacuate. The other time frames don’t meet these specified standby and alarm-load requirements.