Atom
The smallest particle of an element, which can exist alone or in combination.
Backdraft
A phenomenon that occurs when a fire takes place in a confined area, such as a sealed aircraft fuselage, and burns undetected until most of the oxygen within is consumed. The heat continues to produce flammable gases, mostly in the form of carbon monoxide
Black Fire
A hot, high-volume, high-velocity, turbulent, ultra-dense black smoke that indicates an impending flashover or auto ignition.
Boiling Liquid/Expanding Vapor Explosion (BLEVE)
An explosion that occurs when a tank containing a volatile liquid at the bottom of the tank and a flammable gas at the top of the tank is heated to the point where the tank ruptures.
Box
A burning structure
Chemical Energy
Energy that is created or released by the combination or decomposition of chemical compounds.
Class A Fire
A fire in ordinary combustible materials, such as wood, cloth, paper, rubber, and many plastics (NFPA 10).
Class B Fire
A fire in flammable liquids, combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols, and flammable gases (NFPA 10).
Class C Fire
A fire that involves energized electrical equipment (NFPA 10).
Class D Fire
A fire in combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium (NFPA 10).
Class K Fire
A fire in a cooking appliance that involves combustible cooking media (vegetable or animal oils and fats) (NFPA 10).
Combustion
A chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light in the form of either a glow or a flame (NFPA 101).
Compartment
A space completely enclosed by walls and a ceiling. The compartment enclosure is permitted to have openings in walls to an adjoining space if the openings have a minimum lintel depth of 8 inches (203 mm) from the ceiling and the openings do not exceed 8 f
Conduction
Heat transfer to another body or within a body by direct contact (NFPA 921).
Convection
Heat transfer by circulation within a medium such as a gas or a liquid (NFPA 921).
Decay Phase
The phase of fire development in which the fire has consumed either the available fuel or oxygen and is starting to die down.
Electrical Energy
Heat that is produced by electricity.
Endothermic
Reactions that absorb heat or require heat to be added.
Exothermic
Reactions that result in the release of energy in the form of heat.
Fire
A rapid, persistent chemical reaction that releases both heat and light.
Fire Tetrahedron
A geometric shape used to depict the four components of which a fire is composed: fuel, oxygen, heat, and chemical chain reactions.
Fire Triangle
A geometric shape used to depict the three components of which a fire is composed: fuel, oxygen, and heat.
Flameover (Rollover)
The condition where unburned fuel (pyrolysate) from the originating fire has accumulated in the ceiling layer to a sufficient concentration (I.e., at or above the lower flammable limit) that it ignites and burns; it can occur without ignition of, or prior
Flame Point (Fire Point)
The lowest temperature at which a substance releases enough vapors to ignite and sustain combustion.
Flammability Limits (Explosive Limits)
The upper and lower concentration limits (at a specified temperature and pressure) of a flammable gas or vapor in air that can be ignited, expressed as a percentage of the fuel by volume.
Flashover
A transition phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space, resulting in full room involvement or total in
Flash Point
The minimum temperature of a liquid at which sufficient vapor is given off to form an ignitable mixture with the air, near the surface of the liquid or within the vessel used (NFPA 30).
Fuel
A material that will maintain combustion under specified environmental conditions (NFPA 53).
Fully Developed Phase
The phase of fire development in which the fire is free-burning and consuming much of the fuel.
Gas
A material that has a vapor pressure greater than 300 kPa absolute (43.5 psia) at 50 degrees Celsius (122 degrees F) or is completely gaseous at 20 degrees Celsius (68 degrees F) at a standard pressure of 101.3 kPa absolute (14.7 psia) (NFPA 30A).
Growth Phase
The phase of fire development in which the fire is spreading beyond the point of origin and beginning to involve other fuels in the immediate area.
Hypoxia
A state of inadequate oxygenation of the blood and tissue sufficient to cause impairment of function (NFPA 99B).
Ignition Phase
The phase of fire development in which the fire is limited to the immediate point of origin.
Ignition Temperature
Minimum temperature a substance should attain to ignite under specific test conditions (NFPA 921).
Laminar Smoke Flow
Smooth or streamlined movement of smoke, which indicates that the pressure in the building is not excessively high.
Liquid
Any material that (1) has a fluidity greater than that of 300 penetration asphalt when tested in accordance with ASTM D5, Standard Test Method for Penetration of Bituminous Materials, or (2) is a viscous substance for which a specific melting point cannot
Lower Flammable Limit (LFL)
That concentration of a combustible material in air below which ignition will not occur; also known as the lower explosive limit (LEL). Mixtures below this limit are said to be "too lean" (NFPA 329).
Matter
A substance made up of atoms and molecules.
Mechanical Energy
A form of potential energy that can generate heat through friction.
Oxidation
Reaction with oxygen either in the form of the element or in the form of one of its compounds (NFPA 53).
Plume
The column of hot gases, flames, and smoke rising above a fire; also called convection column, thermal updraft, or thermal column (NFPA 921).
Pyrolysis
The destructive distillation of organic compounds in an oxygen-free environment that converts the organic matter into gases, liquids, and char (NFPA 820).
Radiation
The emission and propagation of energy through matter or space by means of electromagnetic disturbances that display both wave-like and particle-like behavior (NFPA 801).
Smoke
The airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion, together with the quantity of air that is entrained or otherwise mixed into the mass (NFPA 318).
Smoke Color
The attribute of smoke that reflects the stage of burning of a fire and the material that is burning in the fire.
Smoke Density
The thickness of smoke. Because it has a high mass per unit volume, smoke is difficult to see through.
Smoke Velocity
The speed of smoke leaving a burning building.
Smoke Volume
The quantity of smoke, which indicates how much fuel is being heated.
Solid
One of three phases of matter; a material that has three dimensions and is firm in substance.
Thermal Column
A cylindrical area above a fire in which heated air and gases rise and travel upward.
Thermal Layering
The stratification (heat layers) that occurs in a room as a result of a fire.
Thermal Radiation
The means by which heat is transferred to other objects.
Turbulent Smoke Flow
Agitated, boiling, angry-movement smoke, which indicates great heat in the burning building. It is a precursor to flashover.
Upper Flammable Limit (UFL)
The highest concentration of a combustible substance in a gaseous oxidizer that will propagate a flame (NFPA 68).
Vapor Density
The weight of an airborne concentration (vapor or gas) as compared to an equal volume of dry air.
Volatility
The ability of a substance to produce combustible vapors.