Emergency voice/alarm communications systems (EVACS) are required to have a secondary power supply capacity of ?.

Emergency voice/alarm communications systems (EVACS) are required to have a secondary power supply capacity of ?.

• A. 1 hour
• B. 2 hours
• C. 4 hours
• D. 8 hours

Answer: (B)

The main idea is that EVACS must keep functioning even when the building’s normal power fails, so it needs a reliable secondary power supply with a defined runtime to support life-safety communications during an emergency. Two hours is specified because evacuation and instruction of occupants can take a significant amount of time, and power outages during fires or other emergencies may last well beyond a few minutes. A two-hour standby capacity ensures the system can continue delivering clear messages and alerts throughout the critical phase of an incident, even if power restoration is delayed. It strikes a practical balance between ensuring reliability and avoiding the need for excessively large, costly batteries. In practice, this secondary power is usually provided by dedicated batteries (and can be backed up by a generator for longer outages) and is designed to operate the EVACS at its rated load for the required duration. Shorter runtimes, like one hour, might not cover the full evacuation window, while much longer runtimes (four or eight hours) would add unnecessary cost for most fire scenarios. So, the best fit is a two-hour secondary power supply, ensuring continuous operation during the critical period of an emergency.

The main idea is that EVACS must keep functioning even when the building’s normal power fails, so it needs a reliable secondary power supply with a defined runtime to support life-safety communications during an emergency.

Two hours is specified because evacuation and instruction of occupants can take a significant amount of time, and power outages during fires or other emergencies may last well beyond a few minutes. A two-hour standby capacity ensures the system can continue delivering clear messages and alerts throughout the critical phase of an incident, even if power restoration is delayed. It strikes a practical balance between ensuring reliability and avoiding the need for excessively large, costly batteries.

In practice, this secondary power is usually provided by dedicated batteries (and can be backed up by a generator for longer outages) and is designed to operate the EVACS at its rated load for the required duration. Shorter runtimes, like one hour, might not cover the full evacuation window, while much longer runtimes (four or eight hours) would add unnecessary cost for most fire scenarios.

So, the best fit is a two-hour secondary power supply, ensuring continuous operation during the critical period of an emergency.