Key Terms

Following is a brief glossary of key terms and concepts used in fire alarm system design.

Addressable Device: A fire alarm system component with discrete identification that can have its status individually identified or that is used to individually control other functions.

Alarm: A warning of fire danger.

Alarm Signal: A signal indicating an emergency requiring immediate action, such as a signal indicative of fire.

Annunciator: A unit containing one or more indicator lamps, alphanumeric displays, or other equivalent means in which each indication provides status information about a circuit, condition, or location.

Authority Having Jurisdiction: The organization, office, or individual responsible for approving equipment, an installation, or a procedure.

Detector: A device suitable for connection to a circuit having a sensor that responds to a physical stimulus such as heat or smoke. Types of detectors include the following:

• Air Sampling-Type Detector: A detector that consists of a piping or tubing distribution network that runs from the detector to the area(s) to be protected. An aspiration fan in the detector housing draws air from the protected area back to the detector through sampling ports, piping, or tubing. At the detector, the air is analyzed for fire productions.

• Combination Detector: A device that either responds to more than one of the fire phenomenon or employs more than one operating principle to sense one of these phenomena. Typical examples are a combination of a heat detector with a smoke detector or a combination rate-of-rise and fixed-temperature heat detector.

• Fire-Gas Detector: A device that detects gases produced by a fire. (genius at work!)

• Fixed Temperature Detector: A device that responds when its operation element becomes heated to a predetermined level.

• Flame Detector: A radiant energy-sensing fire detector that detects the radiant energy emitted by a flame.

• Heat Detector: A fire detector that senses heat produced by burning substances. (Heat is the energy produced by combustion that causes substances to rise in temperature.)

• Line-Type Detector: A device in which detection is continuous along a path. Typical examples are rate of rise pneumatic tubing detectors, projected beam smoke detectors, and heat-sensitive cable.

• Projected Beam-Type Detector: A type of photoelectric light obscuration smoke detector wherein the beam spans the protected area.

• Radiant Energy-Sensing Fire Detector: A device that detects radiant energy (such as ultraviolet, visible, or infrared) that is emitted as a product of combustion reaction and obeys the laws of optics.

• Rate Compensation Detector: A device that responds when the temperature of the air surrounding the device reaches a predetermined level, regardless of the rate of temperature rise.

• Rate-of-Rise Detector: A device that responds when the temperature rises at a rate exceeding a predetermined value.

• Spark/Ember Detector: A radiant energy fire detector that is designed to detect sparks or embers, or both. These devices are normally intended to operate in dark environments and in the infrared part of the spectrum.

Fire Alarm Control Unit (Panel): A system component that receives inputs from automatic and manual fire alarm devices and might supply power to detection devices and a Aux Panel(s) or an off-premises transmitter(s). The control unit might also provide transfer of condition to relays or devices connected to the control unit.  The fire alarm control unit can be a local fire alarm control unit or master control unit.

Fire Alarm Signal: A signal initiated by a fire alarm-initiating device such as a manual fire alarm box, automatic fire detector, waterflow switch, or other device whose activation is indicative of the presence of a fire or fire signature.

Fire Alarm System: A system or portion of a combination system consisting of components and circuits arranged to monitor and annunciate the states of fire alarm or supervisory signal-initiating devices and to initiate the appropriate responses to those signals.

Initiating Device: A system component that originates transmission of a change of state condition, such as in a smoke detector, manual fire alarm box, or supervisory switch. Types of initiating devices include the following:

• Analog Initiating Device (Sensor): An initiating device that transmits a signal indicating varying degrees of condition as contrasted with a conventional initiating device, which can only indicate an on/off condition.

• Nonrestorable Initiating Device: A device whose sensing element is designed to be destroyed in the process of operation.

• Restorable Initiating Device: A device whose sensing element is not ordinarily destroyed in the process of operation. Restoration can be manual or automatic.

• Supervisory Signal-Initiating Device: An initiating device such as a valve supervisor switch, water level indicator, or low-air pressure switch on a dry-pipe sprinkler system whose change of state signals an off-normal condition and its restoration to normal of a fire protection or life safety system; or a need for action in connection with guard tours, fire suppression systems or equipment, or maintenance features of related systems.

Manual Fire Alarm Box: A manually operated device used to initiate an alarm signal.

Notification Appliance: A fire alarm system component such as a bell, horn, speaker, light, or text display that provides audible, tactile, or visible outputs, or any combination thereof. Types of notification appliances include the following:

• Audible Notification Appliance: A notification appliance that alerts by the sense of hearing.

• Visible Notification Appliance: A notification appliance that alerts by the sense of sight.

Notification Appliance Circuit: A circuit or path directly connected to a notification appliance(s).

Power Supply: A source of electrical operating power including the circuits and terminations connecting it to the dependent system components.

Signaling Line Circuit: A circuit or path between any combination of circuit interfaces, control units, or transmitters over which multiple system input signals or output signals, or both, are carried.

Signaling Line Circuit Interface: A system component that connects a signaling line circuit to any combination of initiating devices, initiating device circuits, notification appliances, notification appliance circuits, system control outputs, and other signaling line circuits.

Smoke Alarm: A single or multiple station alarm responsive to smoke.

Smoke Detection: A general term for various means of detecting the smoke from a fire. Methods of smoke detection include the following:

• Ionization Smoke Detection: The principle of using a small amount of radioactive material to ionize the air between two differentially charged electrodes to sense the presence of smoke particles. Smoke particles entering the ionization volume decrease the conductance of the air by reducing ion mobility.  The reduced conductance signal is processed and used to convey an alarm condition when it meets present criteria.

• Photoelectric Light Obscuration Smoke Detection: The principle of utilizing a light source and a photosensitive sensor onto which the principal portion of the source emissions is focused. When smoke particles enter the light path, some of the light is scattered and some is absorbed, thereby reducing the light reaching the receiving sensor. The light reduction signal is processed and used to convey an alarm condition when it meets preset criteria.

• Photoelectric Light-Scattering Smoke Detection: The principle of utilizing a light source and a photosensitive sensor arranged in a manner so that the rays from the light source do not normally fall onto the photosensitive sensor. When smoke particles enter the light path, some of the light is scattered by reflection and refraction onto the sensor. The light signal is processed and used to convey an alarm condition when it meets preset criteria.

Supervisory Signal: A signal indicating the need of action in connection with the supervision of guard tours, the fire suppression systems or equipment, or the maintenance features of related systems.

Zone: A defined area within the protected premises. A zone can define an area from which a signal can be received, an area to which a signal can be sent, or an area in which a form of control can be executed.