Most people have experienced a fire alarm system in action, whether it was during school as part of a planned evacuation drill or an inadvertent alarm during an event. But rarely do people think about the basic functions and components of a fire alarm system.
The basic fire alarm system has four primary purposes:
- Detect a fire
- Alert occupants of the fire condition
- Activate safety control functions
- Alert the local fire department
Some of the functions require complex design and engineering to accomplish, but in all cases these serve as one of the four primary functions.
All the functions of a fire alarm system are accomplished by a series of inputs and outputs. The system inputs consist of fire detection devices and system monitoring devices that activate the control panel and the outputs are responsible for occupant notification and control functions associated with life safety. Many high-rise buildings and other unique occupancies require specialized fire alarm systems and sometimes very complex protection systems; but when the most complex fire alarm system is broken down into the individual components, it is nothing more than a series of inputs and outputs.
Detecting a fire is typically accomplished by installing smoke and/or heat detectors, manual pull stations and automatic sprinkler system water flow switches. Most of us are familiar with smoke and heat detectors because these devices are installed in our homes. Another important detection device is a water flow switch that detects movement of water in the sprinkler piping, typically by a paddle type device that is activated by water moving through a pipe when a sprinkler is activated. The flow causes the paddle of the device to move, thus activating a switch and transmitting an alarm signal to the fire alarm control panel.
Occupant notification is accomplished by the installation of audible notification appliances. These are either horns (the appliance that produces that loud and very annoying sound) or speakers that play a pre-record message and/or allow emergency responders to provide spoken instructions to the occupants. Another key component is visual notification appliances, or strobes as they are referred to in the industry, to provide notification to occupants that are hearing impaired. Each classification of building requires different type of occupant notification system. For more information, refer to NFPA 72, The National Fire Alarm and Signaling Code and the 2010 ADA Standards for Accessible Design.
There are many different types of control functions the typical fire alarm system performs. The activation of a duct mounted smoke detector will shut down the heating ventilation and air conditioning (HVAC) equipment to prevent the migration of smoke to non-affected areas of the building. A smoke detector in an elevator lobby will automatically recall the cars to a designated floor. The activation of smoke detectors could also start fans for smoke exhaust or to pressurize areas to hinder smoke movement.
Fire Department Notification
The codes require fire alarm signals be automatically transmitted directly to the local fire department, or to a central station monitoring service that notifies the fire department of the emergency. This gives the fire department a signal immediately and allows them the opportunity to extinguish the fire before it gets too big.
In conclusion, these are the basic functions and components. More information concerning fire alarm systems can be found in the NFPA 72, The National Fire Alarm and Signaling Code.