NICET Special Hazards II key terms

An electrically nonconductive, volatile extinguishing agent that evaporates after discharge, leaving no residue, and is used where water or powder would damage sensitive equipment or contaminate the space.

A clean agent built from carbon plus halogens such as fluorine, which suppresses fire mainly by absorbing heat from the flame rather than by depleting oxygen in the room.

A clean agent made of naturally occurring gases such as nitrogen, argon, or blends, which extinguishes fire chiefly by lowering the oxygen level in the protected space below the point that supports combustion.

The agent concentration, expressed as a percentage by volume in air, that a total flooding system must achieve and hold to reliably extinguish the hazard, set above the cup burner value by a safety margin.

The minimum agent concentration, determined by a standardized small-scale flame test, that extinguishes a liquid fuel flame; it is the baseline from which the design concentration is calculated.

The highest tested agent concentration at which no measurable harmful physiological effect appears in test animals; it caps the concentration allowed in normally occupied spaces.

The lowest tested concentration at which a harmful physiological effect is observed; it governs whether occupants may remain in a space during discharge and how quickly they must leave.

A fixed system that discharges agent into and holds it within an enclosed volume so the entire protected space reaches the design concentration, rather than applying agent to a specific object.

A door fan or blower door test that measures leakage from the protected room to confirm it can retain the agent at design concentration for the required hold time.

The period during which a total flooding system must keep the agent concentration at or above the design value after discharge, allowing responders time to control the source of the fire.

An audible and visual warning that sounds before agent release, giving occupants time to evacuate and trained staff time to investigate the alarm before the system discharges.

A programmed interval between the alarm and agent discharge, required to give occupants time to leave the space and to allow manual abort where the hazard proves minor.

The time needed for occupants to travel from the protected space to a safe location, used to justify the time delay and to judge whether a space may be occupied during discharge.

A manually operated device that interrupts the discharge sequence after an alarm, allowing a trained operator to stop release when the signal is false or the hazard is small.

A hand-operated station that lets a person start agent discharge on demand, bypassing automatic detection, typically installed at the exit of the protected space.

A detection arrangement requiring two independent signals, usually from detectors in different zones, before the system releases agent, reducing discharges caused by a single faulty detector.

A defined portion of the protected area served by its own detectors, used in cross-zoning logic and to identify where within the space an alarm has originated.

An engineered orifice that distributes agent into the protected space at a designed flow rate and pattern so the required concentration mixes uniformly within the required time.

The hydraulic calculation of agent piping so each nozzle receives the flow and pressure assumed in the design, keeping discharge within the time limit and avoiding excessive pressure at the nozzles.

A header that connects multiple agent cylinders to a common supply pipe, allowing them to discharge together as one system while each cylinder keeps its own valve and actuation.

A pressure vessel storing the extinguishing agent, fitted with a valve, actuation device, and often a pressure gauge and safety relief, sized so the system holds enough agent for the design.

The maximum period allowed for a system to deliver its full agent quantity, set short enough to knock down the fire before it grows but long enough to limit turbulence and pressure surges.

The automatic stopping of fans and closing of dampers serving the protected space before discharge, so agent is not exhausted and the design concentration is not diluted.

A fire in flammable or combustible liquids and gases, such as solvents, fuels, and cooking oils, where the hazard is a fuel surface rather than glowing solid material.

A fire involving energized electrical equipment, where the primary concern is shock risk until power is removed, after which the fire is treated according to the burning material.

A fire in cooking appliances involving combustible cooking media such as vegetable or animal oils and fats, requiring a wet chemical agent that saponifies the surface.

A pre-engineered system that discharges an alkaline solution onto cooking media, reacting with the fat to form a soap-like layer that smothers the fire and cools the surface.

A heat-sensitive device that separates at a rated temperature to actuate detection or release, commonly used over cooking appliances and in pre-engineered system piping.

A hand-operated device that mechanically or electrically actuates a special hazard system when a person discovers fire, required as a backup to automatic detection.

A system using carbon dioxide, which extinguishes mainly by displacing oxygen, and is permitted only in spaces not normally occupied because of its severe asphyxiation hazard.

A system that blankets a flammable liquid surface with a foam blanket, separating fuel from air and cooling it, used for storage tanks, spill areas, and aircraft hangars.

A sprinkler system with open nozzles and a control valve that opens on detection, applying water over an entire area at once rather than only where a sprinkler has fused.

A fixed system using nozzles that produce a directed, finely divided water pattern onto specific equipment or hazards, often for cooling tanks or protecting transformers.

A device that senses a fire signature such as smoke, heat, or flame and sends a signal to the control panel, initiating alarm and, through the panel, discharge logic.

A packaged special hazard system whose components and piping are designed and tested as a unit by the manufacturer, with limits on pipe length, nozzle count, and layout.

The examination of submitted drawings, calculations, and specifications against applicable standards before installation, confirming agent quantity, pipe sizing, and detection are adequate.

The documented on-site verification after installation that the system operates as designed, including detection, alarm, actuation, and, where applicable, enclosure integrity.