How Fire Alarm System Works

A fire alarm system alerts people of a fire by shouting, “Fire!” The system aims to save lives, protect property and minimize damage.

It consists of a control panel, detectors, and notification devices. These devices communicate with the fire alarm control panel through wiring.

Control Panel

The control panel is the heart of the fire alarm systems companies and is responsible for determining how to respond to an emergency. For example, it can sound an evacuation alarm, call the fire department or activate the building’s sprinkler system to try to put out the fire.

Conventional panels represent a building as a series of zones, each with its own detection devices (smoke detectors, heat detectors, pull switches) and associated signaling lines and NACs. When an instrument within a zone activates, the electrical current to the fire alarm panel changes, and an indicator is displayed on the panel to show which area the device has started in.

Addressable Panels and PLC Panels represent a building as a series of regions, with each area having its own “address” in the system and each device sending data rather than simply notifying via a change in electrical current. This allows the fire alarm system to be more detailed and personnel and first responders to identify precisely where a fire is.

Detectors

Fire alarm systems are designed to find fires early in development when time is still available for occupants to evacuate safely. This can save property loss and downtime for building operations and protect emergency response personnel from injury or death.

There are four main types of detectors for a fire alarm system: smoke, heat, fixed temperature, and rate-of-rise. Each has its applications and working principles.

Smoke detectors rely on air ionization when smoke enters the sensing chamber. This disrupts the flow of electrical current within the device, triggering an alarm horn.

Heat detectors likewise use ionization to reduce the flow of electricity in the sensing chamber when smoke enters it. The sensor then sends a signal to the control panel, which triggers the alarm horn.

Rate-of-rise and fixed temperature detectors activate when the room reaches pre-set temperatures. As a result, they are more sensitive than traditional smoke detectors and are less likely to have false alarms.

Notification Devices

Fire alarm notification devices alert building occupants of the need to evacuate in the event of a fire. They may utilize a range of audible, visible, and tactile stimuli such as horns, strobes, bells, and speakers.

Notification appliances are essential to a fire alarm system and can be classified as either addressable or non-addressable. Addressable devices have a unique ID and location, so the control panel can know where to send a signal in an emergency.

Notification appliances are typically connected to a conventional fire alarm system’s Class “A” circuit. A device then supervises them called an end-of-line resistor (ELOR). This resistor keeps the current from going to the notification appliance while not operating.

Backup Batteries

Backup batteries help keep a fire alarm system powered on when the power is out. In addition, they’re used to power hardwired smoke and CO detectors, motion sensors, and security cameras.

The batteries used to provide secondary power for a fire alarm system are usually Valve-Regulated Lead Acid (VRLA) batteries. They’re often located within the control panel enclosure or in a separate battery box.

When a fire alarm system is powered, its backup battery slowly stores power. This way, it’s ready to activate when AC power is lost.

According to NFPA 72, these sealed lead-acid batteries must be replaced every five years. That’s because the battery capacity decreases over time, or the amount of amp hours.