What is the 5 mins of alarm during battery power operation?
It means that all of the horns and strobes must be in alarm continuously for 5 minutes on battery power, after power failure. I think it’s 15 minutes on voice evac.
It is a requirement that the fire alarm system must still be able to support a full 5 minute alarm condition after 24 hours on battery backup. It is a factor that goes into the backup battery calculations when a system is installed.
So let’s say the power went out 24 hours earlier and then a fire is detected. The system must maintain the alarm condition (notification appliances sounding, strobes flashing, etc) for a minimum of 5 minutes without the batteries dying.
Keep in mind this is based on the worst case scenario possible: backup batteries close to or at the end of their useful life, full load on the system, full 24 hours power failure before the alarm, etc.
Does that mean they activate when battery power is low?
Not at all. It must support an alarm condition if it were to occur under these circumstances. It will not CAUSE an alarm.
The batteries could die without any alarms souding at all?
The backup batteries are there for temporary outages but they cannot support the system for a long duration. The hope is that the power will be restored or another backup solution, like an emergency generator, will have taken over in its absence before the batteries are depleted.
Battery failure would never case a fire alarm activation, only a fire (or a manual evacuation of the building for some other cause) elicits this condition.
Oh wow! I never knew that it had to be 5 minutes after a power failure lasting 24 hours! :shock:
From NFPA 72 2007 edition.
4.4.1.5.3* Capacity.
4.4.1.5.3.1 Unless otherwise permitted or required by 4.4.1.5.3.1 (A) or 4.4.1.5.3.1(B), the secondary power supply shall have sufficient capacity to operate the fire alarm system under quiescent load (system operating in a nonalarm condition) for a minimum of 24 hours and, at the end of that period, shall be capable of operating all alarm notification appliances used for evacuation or to direct aid to the location of an emergency for 5 minutes.
(A) The secondary power supply for emergency voice/alarm communications service shall be capable of operating the system under quiescent load for a minimum of 24 hours and then shall be capable of operating the system during a fire or other emergency condition for a period of 15 minutes at maximum connected load.
The AHJ can reduce the required battery standby time to 4 hours if the building fire alarm system receives power from a standby emergency generator. In that case the batteries are providing system power for the time it would take to repair a generator that failed to start automatically.