What is a "Fire Alarm System"?

What is a “Fire Alarm System”?

In this week’s post, with the help of our wonderful Travelling Trainer & new guest blogger, Michael Baker, we’re going back to the basics! For his first post, Michael will be explaining what a fire alarm system is.

Let’s start with the NFPA 72-2013 definition:

3.3.105 Fire Alarm System. A system or portion of a combination system that consists of components and circuits arranged to monitor and annunciate the status of fire alarm or supervisory signal-initiating devices and to initiate the appropriate response to those signals.

Consider a simple box-and-bell system used to evacuate an elementary school building. The school principal notices a trash can fire and immediately pulls the fire alarm manual box, which results in ringing bells throughout the school. The kids instinctively react to the temporal sound by standing up and calmly marching single-file to a muster area.

Here’s what the Fire Alarm System saw during that scenario:

When the manual box was pulled, a short-circuit occurred on the Initiating Device Circuit (IDC). The Fire Alarm Control Unit (FACU) responded to the short circuit by reversing polarity on the Notification Appliance Circuit (NAC), which resulted in bells ringing.

Inputs (manual box, smoke detector, water flow switch) -> FACU -> Outputs (bell, strobe, speaker, chime)

Fire Alarm Systems run the gamut from a simple box-and-bell evacuation system to addressable, analog, voice systems. They all work the same in that the Fire Alarm Control Unit receives signals from devices, modules, and other control units, then processes these signals to satisfy the objective of operating the required system output functions.

NFPA categorizes Fire Alarm Systems as follows:* Combination System. A fire alarm system in which components are used, in whole or in part, in common with a non-fire signaling system.

A. Combination System. Examples of non-fire systems are security, card access control, closed circuit television, sound reinforcement, background music, paging, sound masking, building automation, time, and attendance. Household Fire Alarm System. A system of devices that uses a fire alarm control unit to produce an alarm signal in the household for the purpose of notifying the occupants of the presence of a fire so that they will evacuate the premises. Municipal Fire Alarm System. A public emergency alarm reporting system.* Protected Premises (Local) Fire Alarm System. A fire alarm system located at the protected premises.

A. Protected Premises (Local) Fire Alarm System. A protected premises fire alarm system is any fire alarm system located at the protected premises. It can include any of the functions identified in Section 23.3. Where signals are transmitted to a communication center or supervising station, the protected premises fire alarm system also falls under the definition of one of the following systems: central station service alarm system, remote supervising station alarm system, proprietary supervising station alarm system, or auxiliary alarm system.

The requirements that pertain to these systems apply in addition to the requirements for the protected premises fire alarm systems.

The following two definitions were added in the 2007 code-cycle to make it clear that a fire alarm system may be used for purposes other than evacuation and/or relocation. For example: elevator recall to satisfy the elevator code, fan motor shutdown to satisfy the mechanical code, door release to satisfy the building code, and water flow switch monitoring to satisfy the fire code. When a fire alarm system is used for these other signaling purposes, they are exempt from certain requirements such as a manual box. Building Fire Alarm System. A protected premises fire alarm system that includes any of the features identified in and that serves the general fire alarm needs of a building or buildings and that provides fire department or occupant notification or both. Dedicated Function Fire Alarm System. A protected premises fire alarm system installed specifically to perform emergency control function(s) where a building fire alarm system is not required. Releasing Fire Alarm System. A protected premises fire alarm system that is part of a fire suppression system and/or that provides control inputs to a fire suppression system related to the fire suppression system’s sequence of operations and outputs for other signaling and notification.

Mircom manufactures a wide variety of equipment, to satisfy nearly every requirement, ranging from a simple conventional evacuation fire alarm system to a network of emergency voice systems installed throughout a multi-building campus