What Are the Basics of Fire Alarm Systems?

The most important aspect of fire protection engineering is occupant safety. The best way for a person to survive a fire is to get out of the building as soon as possible. A fire alarm system should not only alert occupants of a fire with an evacuation sound but also call the local fire department to extinguish the fire.

Table of Contents

1. Control Panels

2. Fire Detectors

3. Notification Systems

1. Control Panels

The "brains" of a typical fire alarm system is the control panel. The control panel receives inputs from detectors and decides what the outputs should be. For example, if the control panel receives a certain signal from a duct detector, it will shut down the associated air handling unit and send a notification for maintenance but will not necessarily sound a general evacuation alarm or call the fire department. However, if a control panel finds that the sprinkler system has been activated through a waterflow alarm, it will sound an alarm so the occupants can leave and notify the fire department. The ability of the fire alarm control panel to communicate with authorities is paramount-the sooner the fire department is notified, the faster they can fight the fire and keep it under control. Additionally, the fire alarm control panel can control other building systems, such as recalling elevators to the first floor or activating a smoke control system. The control panel is also a good resource for firefighters to find out where the fire has occurred, as many of them have displays telling which device has been activated. A fire alarm system might also have an annunciator, which is placed at the main entrance of a building to inform responding firefighters on the situation.

2. Fire Detectors

An aspect of fire alarm systems that many people are familiar with are fire detectors, as it is a requirement to have functioning smoke alarms in every residential structure. Smoke alarms provide an audible signal to alert occupants that they should evacuate. In fact, a smoke alarm helped save one of my relatives' homes from certain doom. They had forgotten a pot of food on the stove and left for work-after a couple of hours, the pot began to produce enough smoke to activate the smoke alarms. The neighbors heard the alarm and checked on the house. When they smelled smoke, they called the fire department who promptly arrived and saved the house from serious damage.

Every house should have a smoke alarm in each bedroom to save lives and property. For commercial applications, there are several types of detectors, including smoke, (which sense particles in the air), heat (which trip when a temperature threshold has been reached), and optical detectors (which pick up on infrared or other spectral bands). These detectors send a signal back to the fire alarm control panel. The type of hazard and environment will determine what type of detectors are used. For instance, in a sawmill, a smoke detector might activate constantly with all the dust in the air, so a heat or optical detector might be more appropriate.

3. Notification Systems

Once a detector has sent an alarm signal to the fire alarm control panel, the notification system will activate so that occupants can leave. The device that people are probably most familiar with is the horn/strobe, through which a light will flash and an audible signal will be emitted. Both the light and sound are designed to alert the occupant of the emergency. For high-occupancy buildings such as stadiums or concert halls, a speaker system may be used as well as strobes to provide exact instructions to the occupants. These systems, known as emergency voice/alarm communications systems, can guide occupants to the best exit and provide them more information on the emergency. These systems can also be used by the fire department for crowd control.

Fire alarm systems are integral to fire protection engineering. They save lives and property and give the responding fire department a head start in fighting the fire. Understanding these systems is essential for a safely built environment.

About the Author: Nick Tran

Nick Tran is a licensed Mechanical and Fire Protection Engineer in California. He has an Associates degree in Computer Aided Design from De Anza College, a Bachelor of Science degree in Mechanical Engineering from San Jose State, and a Master of Science degree in Fire Protection Engineering from Cal Poly SLO. He is currently on the UL Standards Technical Panel for UL 38 and was president of the Alameda County Fire Prevention Officers Association.