NFSC Sub-Officer Entrance key terms

The sudden transition in a compartment fire where all exposed combustible surfaces ignite almost simultaneously, producing a room fully involved in flame and a rapid, steep rise in temperature.

A sudden explosion-like ignition of accumulated hot gases when air is admitted to a fire in a poorly ventilated, oxygen-starved compartment, driving flame out of the openings.

Chemical decomposition of a solid fuel by heat in the absence of oxygen, releasing flammable gases and vapours that then burn in the flame zone.

The three elements needed for combustion: fuel, oxygen and heat. Removing any one of them extinguishes or prevents fire, and the model underlies most extinguishing methods.

An extension of the fire triangle adding the chemical chain reaction as a fourth element, used to explain why chemical extinguishing agents such as dry powder stop flaming combustion.

A layer of foam, gas or vapour held over a liquid fuel surface that separates the fuel from oxygen and suppresses the release of flammable vapour.

The lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture with air near its surface, without the vapour continuing to burn.

The temperature slightly above the flash point at which a liquid releases vapour fast enough to sustain continuous burning once ignited.

The range between the lower and upper concentration limits of fuel vapour in air within which ignition can occur; outside this band the mixture is too lean or too rich to burn.

The mass of a vapour or gas compared with an equal volume of air. Values above one mean the vapour is heavier than air and tends to collect in low-lying areas.

Rapid ignition of a pre-mixed cloud of unburnt smoke and air inside a compartment, producing a pressure wave without the inflow of fresh air that characterises a backdraught.

The speed at which a material loses mass or releases heat per unit area per unit time while burning, used to estimate fire growth and required extinguishing application rates.

The rate at which a fire liberates thermal energy, usually expressed in kilowatts or megawatts, and the main measure of fire size and growth potential.

The total heat energy that could be released by burning all combustible contents and linings within a compartment, usually expressed per unit floor area.

Dividing a building into fire-resisting compartments by walls, floors and doors so that fire and smoke are held in the area of origin for a defined period.

A door assembly with a stated fire resistance rating, fitted with self-closing and intumescent or smoke-sealing devices, that maintains the integrity of a compartment wall when closed.

The period in minutes or hours for which a structural element or assembly resists fire under test, judged on stability, integrity and insulation criteria.

The permanent, static weight of a structure itself, including walls, floors, roofs and fixed services, that the building must always carry.

The variable weight imposed on a structure by occupants, furniture, stored goods and movable equipment, which changes over time and is allowed for in design.

The ground area around a damaged building where debris could fall or walls could topple, calculated as a distance at least equal to the structure's height.

Temporary timber, steel or pneumatic props placed to support weakened walls, floors or trenches during rescue work to protect casualties and rescuers.

The specialised operation of freeing a person trapped in an excavated trench, requiring collapse protection, shoring and avoidance of loading the sides.

The process of releasing and removing a trapped casualty from a vehicle, structure or machinery using hydraulic, pneumatic or manual cutting and spreading tools.

A pressure surge caused by a sudden change in water velocity in a pipe or hose, producing a loud knock and possible damage to fittings and appliances.

A valved connection on a water main, above or below ground, from which firefighting crews draw water into pumps or appliances through hose.

A flexible hose that carries water from a pump or appliance to a branch or nozzle under pressure, as distinct from a suction hose.

Two nozzle settings: a solid jet throws water far and penetrates deep-seated fire, while a spray or fog pattern absorbs heat, protects crews and disperses vapour clouds.

The controlled release of heat, smoke and hot gases from a compartment by opening or cutting openings, improving visibility and reducing the risk of flashover or backdraught.

A fixed piping network with heat-actuated heads that automatically discharge water onto a fire, controlling or extinguishing it before crews arrive.

A vertical pipe installed in a building, kept charged with water and fitted with landing valves so crews can connect hose on upper floors without long hose runs.

A low wall or embankment around a storage tank or drum area that contains spilled liquid and firefighting water, preventing it from spreading to drains or other risks.

A three-character emergency action code on vehicles and containers carrying dangerous goods, telling responders which extinguishing medium and protective measures to use.

A four-digit identification number assigned to a dangerous good or article, marked on packages and transport documents to identify the substance quickly in an emergency.

Force acting per unit area, measured in pascals; in fire service work it explains nozzle reaction, hose friction loss and the lift available from a pump.

The heat energy needed to raise the temperature of one kilogram of a substance by one kelvin, explaining why water absorbs large amounts of heat when extinguishing fire.

The energy absorbed when a liquid changes to vapour at its boiling point without a temperature change; water's high value makes steam production a powerful cooling mechanism.

A conclusion drawn from stated evidence rather than stated directly; comprehension questions often ask what can be reasonably inferred from a passage.