In terms of survivability, fire alarm circuits must operate for at least how long?

The requirement for fire alarm circuits to operate for at least two hours is rooted in ensuring that the systems maintain functionality during a fire event. This timeframe is critical for survivability, as it allows for not only the alerting of occupants but also the effective notification to emergency services and the overall response strategy.

Operating for two hours ensures that the fire alarm system can function during the initial stages of a fire, when conditions may be most dangerous. It supports the essential roles of detection, notification, and potential building evacuation, which are all key in minimizing risks to life and property.

Standards and building codes, including those established by the National Fire Protection Association (NFPA), emphasize this duration for reliable and effective operation under adverse conditions. This reflects the real-world need for a safety period that accommodates for the time it might take for a building to be evacuated and for first responders to arrive and act.