NFPA Firefighter I key terms

Model showing the four components required for flaming combustion: fuel, oxygen, heat, and the self-sustaining chemical chain reaction. Removing any one of the four components stops the fire.

The chemical breakdown of a solid material caused by heat, which releases combustible gases and vapors before the material actually ignites. It explains why solid fuels burn as gases.

The lowest temperature at which a material will begin to burn on its own without a spark, flame, or other external ignition source, given sufficient time and oxygen.

The lowest temperature at which a liquid releases enough vapor to form a flammable mixture with air near its surface, allowing a brief flash when an ignition source is applied.

The minimum concentration of a flammable vapor or gas in air, usually expressed as a percentage, that will ignite. Below this level the mixture is too lean to burn.

A transition in a compartment fire in which heat feedback ignites all exposed combustible surfaces almost at once, causing full-room involvement and a sudden, steep rise in temperature.

The ignition of hot, accumulated fire gases at ceiling level as they mix with air, producing flames that spread rapidly overhead ahead of the main body of fire.

A sudden explosion of fire gases that occurs when air is admitted to an overheated, oxygen-starved compartment, igniting the accumulated fuel-rich smoke and pushing fire outward.

Boiling liquid expanding vapor explosion. A pressure vessel containing liquid fails from flame impingement, releasing vapor that ignites into a fireball with fragments thrown long distances.

Immediately dangerous to life or health. An atmosphere that poses an immediate threat of severe exposure, death, or irreversible health effects, or that impairs a person's ability to escape.

Self-contained breathing apparatus. A portable backpack unit that supplies filtered compressed air from a cylinder through a regulator so the wearer can breathe safely in contaminated atmospheres.

Personal alert safety system. A motion-sensing alarm worn by firefighters that sounds a loud signal if the wearer stops moving for a set period, helping rescuers locate a downed member.

The radio term used to declare that a firefighter is lost, trapped, out of air, or otherwise in immediate life-threatening danger, which triggers emergency rescue procedures on the fireground.

A team of at least two firefighters, staged with full equipment, whose only job is to rescue trapped or injured personnel. Required at structure fires under two-in/two-out rules.

An OSHA requirement that at least two firefighters remain outside a hazardous atmosphere, ready to rescue, whenever two enter, until a second crew arrives and a rescue capability exists.

The ensemble of coat, trousers, helmet, hood, gloves, and boots designed to shield firefighters from heat, flame, and water. It does not protect against every hazard by itself.

The National Fire Protection Association standard that sets minimum design, performance, and testing requirements for protective ensembles used in structural firefighting and proximity firefighting.

A standardized, modular management system that assigns clear roles, span of control, and communications so multiple agencies can work together safely and efficiently at an emergency scene.

The ongoing process of gathering and evaluating information about an incident, such as construction, occupancy, fire location, and resources, to form an action plan before and during operations.

The planned and systematic release of heat, smoke, and fire gases from a structure with replacement by fresher air, which improves visibility, tenability, and the effectiveness of fire attack.

Opening the roof or upper level directly above the fire so hot gases and smoke vent upward. It improves interior conditions but must be coordinated with fire attack.

A fast, systematic sweep of the fire area and likely occupied spaces, done early and often under poor visibility, to find and remove victims who are still alive.

The stage after fire control in which crews open concealed spaces, remove smoldering debris, and check for hidden fire to prevent rekindle before leaving the scene.

Protecting property from water, smoke, and damage during and after a fire by covering contents, catching runoff, and moving valuables to a safe location.

The pressure lost as water moves through hose, pipes, and fittings because of turbulence and contact with the walls. It increases with flow rate, hose length, and smaller hose diameter.

The pressure the pump must produce so the nozzle receives the desired pressure after friction loss and elevation changes are taken into account by the operator.

The voltage difference across the surface of the ground around an energized conductor, greatest near the contact point. Firefighters use a shuffle step or hop to avoid step potential.

A space large enough to enter, with limited entry or exit, and not designed for continuous occupancy. Many require permits, atmospheric testing, attendants, and retrieval systems before entry.

Stacked wooden or composite blocks used to support, stabilize, and hold lifted objects such as vehicles or collapsed structures so rescuers can work safely beneath them.

The process of preventing a vehicle from moving or shifting during extrication by chocking wheels, setting the parking brake, and placing cribbing or struts at key contact points.

The location inside a structure or vehicle where a fire began, identified through burn patterns, damage analysis, and witness information. It is the starting point of a cause determination.

A fire that was intentionally set under circumstances in which the person knew it should not be ignited. It is one of the cause classifications used in fire investigation.

A foam concentrate designed for flammable liquid fires. It forms a blanket over the fuel surface that smothers vapor, separates fuel from oxygen, and helps prevent reignition.

The process of mixing foam concentrate with water at the correct percentage, such as 1, 3, or 6 percent, before the solution reaches the nozzle or the air-aspirating device.

Drawing water from a static source such as a pond, pool, or portable tank by using a pump to create a partial vacuum, since the water source itself is not pressurized.

A tanker-based supply operation in which apparatus carry water from a fill site to a portable tank at the fire scene and then return for more, moving water where hydrants are unavailable.

Piping built into a building that provides firefighters with a hose connection at each floor, letting them attach hose and obtain water without stretching lines from the street.