Fire Protection Glossary

AHJ (Authority Having Jurisdiction)

The local official, office, or agency (typically the fire marshal or building department) responsible for enforcing fire and building codes and approving system designs and installations in a given jurisdiction.

Backflow Preventer

A device installed where a fire sprinkler system connects to the potable water supply, preventing stagnant sprinkler-system water from siphoning back into the drinking water system. See our full Backflow Prevention guide.

Clean Agent

A gaseous fire suppression agent (such as FM-200 or Novec 1230) that extinguishes fire without water or residue, commonly used in data centers and other sensitive-equipment spaces. See Clean Agent & Gaseous Fire Suppression.

Deluge System

A sprinkler system in which all heads are open at all times; when the fire detection system activates, water discharges from every head simultaneously. Used in high-hazard areas like aircraft hangars and chemical storage. See Fire Sprinkler System Types.

Dry Pipe System

A sprinkler system with pipes filled with pressurized air or nitrogen instead of water, used in unheated spaces where water could freeze, such as parking garages and cold storage.

Fire Department Connection (FDC)

A fitting on the exterior of a building that lets fire crews pump additional water into a building’s sprinkler or standpipe system during a fire. See Fire Department Connections.

Fire Pump

A pump that boosts water pressure and flow to meet a sprinkler or standpipe system’s hydraulic demand when the existing water supply can’t do it alone, tested under NFPA 20. See Fire Pump Systems.

Fire Watch

A temporary safety measure, typically a trained person patrolling a building at set intervals, used when a fire protection system is out of service or impaired, until the system is restored. See our full post on what a fire watch involves and when one is required.

Hazard Classification

A rating (light, ordinary, or high hazard) assigned to a building or space based on the amount and combustibility of its contents, which determines sprinkler system design requirements under NFPA 13.

Hydraulic Calculation

The engineering calculation used to size pipes and confirm water pressure and flow will meet a sprinkler system’s design demand at every sprinkler head.

ITM (Inspection, Testing, and Maintenance)

The ongoing cycle of inspecting, testing, and maintaining fire protection systems required by NFPA 25 and similar standards to confirm they will function correctly in a fire.

NFPA (National Fire Protection Association)

The nonprofit organization that develops and publishes the fire protection standards (such as NFPA 13, 25, 20, 72, and 96) referenced throughout this site and adopted, in whole or in part, by most U.S. jurisdictions.

Notification Appliance

A fire alarm system component, such as a horn, strobe, or combination horn/strobe, that alerts building occupants when the alarm activates.

Occupancy Classification

The building code category (such as business, assembly, storage, or healthcare) assigned to a building based on its use, which affects which fire protection systems are required.

Post Indicator Valve (PIV)

An above-ground control valve for an underground fire sprinkler supply line, with an indicator showing whether the valve is open or closed at a glance.

Pre-Action System

A sprinkler system requiring two events, a fire detection signal and heat at the sprinkler head, before water enters the pipes and discharges, adding protection against accidental discharge. Common in data centers and archives.

Riser

The vertical pipe that carries water from a building’s water supply up through the fire sprinkler or standpipe system, typically the main point of connection and control valves.

Sprinkler Head

The individual device mounted on sprinkler piping that releases water when triggered by heat, typically via a heat-sensitive glass bulb or fusible link.

Standpipe System

A system of piping and hose connections, in Class I, II, or III configurations, that delivers water throughout a building primarily for fire department use. See Standpipe Systems.

Suppression System

Any fixed system designed to extinguish or control fire, including water-based sprinklers as well as specialized systems like clean agent and wet chemical kitchen hood systems.

UL Listing

Certification from UL (Underwriters Laboratories) indicating a fire protection product or system has been independently tested and meets applicable safety standards. See why UL listings matter for fire protection equipment.

Water Flow Switch

A device on a sprinkler system that detects water movement in the pipe (indicating a sprinkler has activated) and signals the fire alarm system.

Wet Chemical System

A fire suppression system using a liquid chemical agent, most commonly installed over commercial kitchen cooking equipment to suppress grease fires. See Commercial Kitchen Fire Suppression.

Wet Pipe System

The most common type of commercial fire sprinkler system, in which water is held in the pipes at all times and discharges immediately when a sprinkler head activates. Compare it with dry pipe systems in our post on wet pipe vs. dry pipe sprinklers.