To limit the probability that, during a failure of the normal power supply to a fire alarm system, the fire alarm system will not be capable of performing its intended functions for a length of time sufficient for normal power to be restored, which could lead to emergency responders not being promptly notified of a fire situation, which could lead to delays or ineffectiveness in carrying out fire emergency response operations, which could lead to the spread of fire, which could lead to damage to the building.