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Autoignition Temperature

Same as ignition temperature except that no external ignition source is required for ignition because the material itself has been heated to ignition temperature.


Instantaneous explosion or rapid burning of superheated gases that occurs when oxygen is introduced into an oxygen-depleted confined space. The stalled combustion resumes with explosive force. It may occur because of inadequate or improper ventilation procedures.

Boiling Liquid Expanding Vapor Explosion (BLEVE)

Rapid vaporization of a liquid stored under pressure upon release to the atmosphere following major failure of its containing vessel. The failure of the containing vessel is the result of over-pressurization caused by an external heat source causing the vessel to explode into two or more pieces when the temperature of the liquid is well above its boiling point at normal atmospheric pressure.

Carbon Dioxide (CO2)

Colorless, odorless, heavier than air gas that neither supports combustion nor burns. CO2 is used in portable fire extinguishers as an extinguishing agent to extinguish Class B or C fires by smothering or displacing the oxygen.


Physical flow or transfer of heat energy from one body to another through direct contact or an intervening medium from the point where the heat is produced to another location or from a region of high temperature to a region of low temperature.


Transfer of heat by the movement of heated fluids or gases usually in an upward direction.

Endothermic Heat Reaction

Chemical reaction in which a substance absorbs heat energy.

Exothermic Heat Reaction

Chemical reaction between two or more materials that changes the materials and produces heat flames, and toxic smoke.

Fire Point

Temperature at which a liquid fuel produces sufficient vapors to support combustion once the fuel is ignited. The fire point is usually a few degrees above the flash point.

Fire Tetrahedron

Model of the four elements/conditions required to have a fire. The four sides of the tetrahedron represent fuel, heat, oxygen, and chemical chain reaction.

Flammable Range

The range between the upper flammable limit and lower flammable limit in which a substance can be ignited.

Flash Point

Minimum temperature at which a liquid gives off enough vapors to form an ignitable mixture with air near the liquid's surface.


Stage of a fire at which all surfaces and objects within a space have been heated to their ignition temperature and flame breaks out almost at once over the surface of all objects in the space.

Heat Release Rate (HRR)

Total amount of heat produced or released to the atmosphere from the convective-lift fire phase of a fire per unit mass of fuel consumed per unit time.

Incipient Phase

First phase of the burning process in a confined space in which the substance being oxidized is producing some heat but the heat has not spread to other substances nearby. During this phase, the oxygen content of the air has not been significantly reduced.

Kinetic Energy

The energy possessed by a moving object.


Anything that occupies space and has mass.


Materials that are capable of being mixed.

Potential Energy

Stored energy possessed by an object that can be released in the future to perform work once released.


The transmission or transfer of heat energy from one body to another body at a lower temperature through intervening space by electromagnetic waves such as infrared thermal waves, radio waves, or X-rays.

Reducing Agent

The fuel that is being oxidized or burned during combustion.


Condition in which the unburned combustible gases released in a confined space (such as a room or aircraft cabin) during the incipient or early steady-state phase and accumulate at the ceiling level. These superheated gases are pushed, under pressure, away from the fire area and into uninvolved areas where they mix with oxygen. When their flammable range is reached and additional oxygen is supplied by opening doors and/or applying fog streams, they ignite and a fire front develops, expanding very rapidly in a rolling action across the ceiling.


A phenomenon that occurs when mixtures of alkaline based chemicals and certain cooking oils come into contact resulting in the formation of a soapy film.


Degree to which a solid, liquid, or gas dissolves in a solvent (usually water).

Specific Gravity

Weight of a substance compared to the weight of an equal volume of water at a given temperature. A specific gravity less than 1 indicates a substance lighter than water; a specific gravity greater than 1 indicates a substance heavier than water.

Thermal Layering (of Gases)

Outcome of combustion in a confined space in which gases tend to form into layers according to temperature, with the hottest gases are found at the ceiling and the coolest gases at floor level.


Process of evolution that changes a liquid into a gaseous state. The rate of vaporization depends on the substance involved, heat, and pressure.

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