Commercial Fire Alarm Basics: What Is Initiation?

As a business owner, your fire alarm system is one of the most critical life safety components within a building — second only perhaps to functioning exit doors. Most of us have grown up with fire alarms and understand how they work; however, as a business owner with legal and ethical responsibility for people within your building, you must have some understanding of how it functions.

There are six parts of the modern commercial fire alarm: initiation, supervision, power supply, notification, emergency control function, and off-premise signaling. In this first post in the series, we’ll walk you through initiation.

What Is Initiation in a Fire Alarm?

The initiation section of the fire alarm reports the status of the area in which you have sensors. We call this the protected space. You’ll find initiations in all kinds of detectors (CO, heat, water leak, etc.).

When the sensors detect a “threat,” they initiate either a/an:

  1. Alarm condition: There is a current threat to alert people about.
  2. Supervisory condition: There is an issue within the system itself, such as a closed sprinkler valve.

Initiation in Conventional Vs. Addressable Systems

In the conventional system, a switch contacts both sides of the initiating device to make a circuit (a completed path of electricity). The FACU (Fire Alarm Control Unit) understands this connection to mean there is an alarm condition. Once this happens, no other devices in the area can send a signal. This helps responders identify where the threat is in a building.

Conversely, the addressable systems can communicate an identifiable code(s) to specify which device(s) picked up a threat. However, unlike conventional, one device sending an alert signal doesn’t keep others from doing so in cases of simultaneous threats.

What’s more, some addressable systems can assess the severity of the situation, such as measuring smoke density or heat.

How Initiator Detects a Threat

Here are some common ways this happens:

  • Ionization Smoke Detector – Trace amounts of radioactive particles allow the device to detect a reduction in current.
  • Photoelectric Smoke Detector – Light scatters, indicating a threat.
  • Beam Smoke Detector – A light beam breaks.
  • Fixed Temperature Heat Detector Non-Restorable – Solder melts at a certain temperature, causing a plunger to lower.
  • Fixed Temperature Heat Detector Restorable – Two metals expand with different amounts of heat, lowering a plunger. They return their original shape after.
  • Rate-of-Rise Heat Detector – Chambers measure temperature elevation and close a chamber, when the threshold is reached.

Do you know how your building’s fire alarm works? We encourage you to check out other parts in our series, and if you have questions please visit or reach out to us at  [email protected].