Reference
Leer en españolFire Alarm Glossary
The terms behind the panel: what they mean, where NFPA 72 covers them, and which guide or quiz to open next.
45 terms
A
A-weighted Decibel (dBA)Sound level measured with the A-weighting curve, which approximates human hearing. Public mode audible signals must be at least 15 dBA above average ambient or 5 dBA above the maximum 60-second sound level, whichever is greater.Acceptance TestThe 100 percent functional test of every device and function witnessed by the AHJ before a new or modified system is placed in service.Alarm CurrentCurrent drawn with all notification appliances and relays active. Multiplied by alarm minutes (as a fraction of an hour) in a battery calculation and used for NAC voltage-drop sizing.Alarm SignalA signal indicating an emergency requiring immediate action, such as a fire. It has priority over supervisory and trouble signals and triggers notification appliances and emergency control functions.Authority Having JurisdictionAHJThe organization, office or individual responsible for enforcing the code and approving equipment and installations — typically the fire marshal or building official. Their adopted edition and amendments govern.
C
Candela (cd)The unit of luminous intensity used to rate visible notification appliances (strobes). NFPA 72 tables give the required candela for a room size and mounting height so occupants with hearing loss are alerted.Class A PathwayA circuit with a redundant return path to the panel. A single open or ground fault does not stop devices beyond the fault from operating, and the panel reports a trouble. Costs more cable but keeps the system working under a single fault.Class B PathwayA circuit that ends at an end-of-line device with no return path. A single open prevents devices beyond the break from reporting; the panel detects the fault as a trouble. The most common and lowest-cost pathway class.Class N PathwayPathway class for network (IP/Ethernet) based systems with redundant communication paths and supervised links, introduced for emergency communications and networked panels.Class X PathwayA Class A pathway with added isolation so that a single short circuit also does not take down the loop. Common for SLCs in high-value or high-rise applications.
D
Digital Alarm Communicator TransmitterDACTThe dialer that sends alarm, supervisory and trouble signals to the supervising station over phone lines or, increasingly, cellular/IP communicators. Must test its path at least every 6 hours (24 h for some arrangements).Duct Smoke DetectorA smoke detector sampling air inside HVAC ductwork to shut down air handlers and prevent smoke circulation. Requires a remote test/indicator where the housing is not visible.
E
Elevator RecallEmergency control function that returns elevators to the designated level (or alternate level if the lobby detector is in alarm) when smoke detectors in lobbies, machine rooms or hoistways activate.Emergency Communications SystemECSA system that delivers voice or text instructions for emergencies — in-building fire emergency voice/alarm communications (EVACS) and mass notification systems (MNS).End-of-Line DeviceEOLThe resistor (or diode/capacitor) installed at the electrical end of a Class B circuit. The panel measures the small supervisory current through it; an open removes the current (trouble), a short increases it (alarm or trouble depending on circuit type).End-of-Line VoltageThe voltage measured at the last appliance on a NAC under full alarm load. The practical pass/fail number of a voltage-drop calculation.
F
G
H
I
ImpairmentA condition where a fire protection system or part of it is out of order. Requires notification of the AHJ, supervising station and building occupants, and a tag on the panel until restored.Initiating Device CircuitIDCA conventional circuit that connects initiating devices (pull stations, smoke and heat detectors, waterflow switches) to the panel. Devices simply close or change the circuit; the panel knows a zone is in alarm but not which device. Supervised with an end-of-line device.IntelligibilityHow clearly voice messages can be understood, measured with STI/CIS. Voice systems must be intelligible in acoustically distinguishable spaces, not merely loud.Isolator ModuleAn SLC device that opens the loop on either side of a short circuit so the rest of the addressable loop keeps working. Required to meet Class X and often used to limit the devices lost to one fault.
M
Manual Fire Alarm Box (Pull Station)A manually operated initiating device. Required within 5 ft of each exit door on each floor, mounted 42–48 in to the handle, with travel distance not exceeding 200 ft on any floor.Monitor (Input) ModuleAn addressable module that puts a conventional contact — waterflow switch, tamper switch, pull station — onto the SLC with its own address.
N
P
Plenum-Rated Cable (FPLP)Power-limited fire alarm cable listed for use in ducts, plenums and other air-handling spaces because of its low smoke and flame spread. FPLR is for risers and FPL for general use.Power-Limited Fire Alarm CircuitPLFAA fire alarm circuit supplied by a listed power-limited source, allowing smaller wiring methods and cable types under NEC Article 760 Part III.Projected Beam Smoke DetectorA transmitter/receiver pair (or reflector) that detects smoke obscuring a light beam across a large open space such as an atrium or warehouse.
R
Record of CompletionThe NFPA 72 form documenting the installed system, its components, circuits, power supplies and test results, completed at acceptance and kept on site.Relay (Control) ModuleAn addressable module with dry contacts that the panel operates to control doors, fans, elevators or other equipment as part of the sequence of operation.
S
Secondary Power SupplyBatteries (or generator) that keep the system running when primary AC fails: 24 hours of standby followed by 5 minutes of alarm for most systems, 15 minutes of alarm for emergency voice systems.Sequence of OperationsThe matrix that defines what every input does to every output — which detectors recall elevators, release doors, shut down fans and sound which appliances. The single most useful commissioning document.Signaling Line CircuitSLCThe addressable data loop of an analog/addressable system. Each detector, module and pull station has an address, so the panel knows exactly which device is in alarm and can read smoke sensitivity values. Isolators limit the effect of a short.Smoke Detector Sensitivity TestVerification that a smoke detector's response is within its listed sensitivity range — using a calibrated test method, the panel's analog values or a listed test instrument. Required within one year of installation, then every alternate year.Spot-Type Smoke DetectorA detector that senses smoke at a single point using ionization or photoelectric sensing. Spacing is nominally 30 ft (9.1 m) on smooth ceilings, reduced for beams, slopes and airflow.Standby (Supervisory) CurrentCurrent drawn by the panel and all connected devices in the normal, non-alarm condition. Multiplied by the standby hours in a battery calculation.Supervising StationA facility that receives signals from protected premises and dispatches response — central station, proprietary or remote supervising station. Requires two communication paths or a single path that meets specific performance criteria.Supervisory SignalA signal that indicates something that affects the fire protection system needs attention but is not a fire — for example a closed sprinkler valve, low air pressure or a disabled duct detector. Distinct from alarm and trouble.
T
Temporal-Four PatternT-4The four-pulse carbon monoxide alarm signal pattern, used to distinguish CO alarms from fire evacuation signals.Temporal-Three PatternT-3The standard evacuation signal: three half-second pulses, a 1.5-second pause, repeated. Required for fire alarm evacuation signals so occupants recognise the same pattern everywhere.Trouble SignalA signal indicating a fault in the system or its pathways: open circuit, ground fault, low battery, loss of AC power, communication failure. Must be indicated within 200 seconds and is distinct from alarm and supervisory signals.
V
Valve Supervisory (Tamper) SwitchA switch that reports a supervisory signal when a sprinkler control valve moves off the fully open position, so a closed valve is never silent.Voltage DropLoss of voltage along a conductor due to its resistance. On a NAC the last appliance must still see its minimum rated voltage (often 16 V on a 24 V system) at the end of battery life.