Innovations in fire safety: exploring survivability and alarms

Learn to navigate NFPA 72 by understanding the evolving landscape of fire alarm circuit survivability

By Consulting-Specifying Engineer January 30, 2024
Survivability may require occupant evacuation. Courtesy: Amara Rozgus, CFE Media and Technology

Survivability insights

  • In cases of partial evacuation or relocation, survivability is necessary, ensuring communication integrity during relocation.
  • Different scenarios, such as using two-hour rated cable or separating equipment and cabling by fire-rated constructions, offer flexibility in meeting these requirements, including options for nonrated cable in certain situations, as outlined in the updated code.

The survivability requirements for fire alarm circuits in NFPA 72: National Fire Alarm and Signaling Code vary based on the evacuation strategy. Learn about survivability from Ray Grill, PE, Principal, Ray Grill Consulting, Clifton, Virginia.

Read the transcript of this webcast, and watch the on-demand event here. This transcript has been edited for length and clarity.

There have been a lot of changes in survivability over the years. Survivability of the circuits for notification are only required in NFPA 72 when you are doing partial evacuation or relocation. If you are doing total evacuation in a building with your fire alarm system, then survivability is not required. The whole idea is that if you relocate someone, you still need to be able to communicate with them. You are typically relocating them to another floor, so the circuits must be able to maintain their integrity from fire so that subsequent messages can be delivered.

For example, if we have class B wiring, which is not redundant, we can have our fire alarm equipment and our circuits runs in a stacked electrical room where the electrical rooms are two hours, so they are basically creating a shaft for all practical purposes. We only then would need to provide two-hour rated cable when we come out of that shaft. Between the fire alarm control panel, we would need two-hour cable in this scenario.

Another option would be having our fire alarm equipment within two-hour rated rooms and then our interconnection of that equipment would be using a fire rated cable. The cable on the floor that connects to the devices. It is not typically required to be rated because it is only serving one compartment. If we have a fire on the floor and it ultimately destroys those circuits, we might need isolation modules so that a short circuit does not take out the entire system, but we would not be providing rated conductors on those floors.

Now the code also added some additional options. In a sprinkler building we can have class X wiring, which is a redundant run, and there’s also isolation modules between the elements so that if we do have a short circuit, the system can still perform. We would have to have our equipment in two-hour rated and closures, but our cabling would not have to be rated if we can separate the outgoing and the return runs by at least one-third the diagonal dimension of the notification zone through which they are passing.

There are some options that have been added to the code that allow for nonrated cable. Another option that has been added, now this is for a sprinkler or nonsprinkler building, we can have class X wiring, we can have our equipment in one hour or rather in two-hour rated rooms, and we can have cable and conduit that is separated by one-hour rated construction. That is an option that is also incorporated in the standard now.