Ch-5

Common, prevailing, and uncontrolled atmospheric weather conditions. The term may refer to the conditions inside or outside of the structure.

Ambient conditions

Initiation of combustion by heat but without a spark or flame. (NFPA® 921)

Autoignition

The lowest temperature at which a combustible material ignites in air without a spark or flame. (NFPA® 921)

Autoignition temperature

The explosive burning of heated gases that occurs when oxygen is introduced into a compartment that has a high concentration of flammable gases and a depleted supply of oxygen due to an existing fire

Backdraft

The tendency or capacity to remain afloat in a liquid or rise in air or gas.

Buoyant

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

Carbon dioxide

Colorless, odorless, dangerous gas (both toxic and flammable) formed by the incomplete combustion of carbon. It combines with hemoglobin more than 200 times faster than oxygen does, thus decreases the blood's ability to carry oxygen

Carbon monoxide

A relatively thin layer of flowing hot gases that develops under a horizontal surface (e.g., ceiling) as a result of plume impingement and the flowing gas being forced to move horizontally. (NFPA® 921)

Ceiling jet

Extinguishment of a fire by interruption of the chemical chain reaction

Chemical flame inhibition

Liquid having a flash point at or above 100°F (37.8°C) and below 200°F (93.3°C).

Combustible liquid

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 flame. (Reproduced with permission from NFPA® 921-2011, Guide for Fire and Explosion Investigations, Copyright�, National Fire Protection Association®)

Combustion

Transfer of heat through or between solids that are in direct contact.

Conduction

Heat transfer by circulation within a medium such as a gas or a liquid. (NFPA® 921)

Convection

Chemical reaction that absorbs thermal energy or heat.

Endothermic reaction

Capacity to perform work; occurs when a force is applied to an object over a distance, or when a chemical, biological, or physical transformation is made in a substance.

Energy

Chemical reaction that releases thermal energy or heat.

Exothermic reaction

A rapid oxidation process, which is a chemical reaction resulting in the evolution of light and heat in varying intensities. (NFPA® 921)

Fire

Temperature at which a liquid fuel produces sufficient vapors to support combustion once the fuel is ignited. Fire point must exceed 5 seconds of burning duration during the test. The fire point is usually a few degrees above the flash point.

Fire point

The explosive burning of heated gases that occurs when oxygen is introduced into a compartment that has a high concentration of flammable gases and a depleted supply of oxygen due to an existing fire

Fire tetrahedron (Mr. Tetrahedron's model ;D)

A model used to explain the elements/conditions necessary for combustion. The sides of the triangle represent heat, oxygen, and fuel.

Fire triangle

Visible, luminous body of a burning gas emitting radiant energy including light of various colors given off by burning gases or vapors during the combustion process.

Flame

Any liquid having a flash point below 100°F (37.8°C) and a vapor pressure not exceeding 40 psi absolute (276 kPa) {2.76 bar}.

Flammable liquid

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

Flammable range

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

Flash point

A rapid transition from the growth stage to the fully developed stage.

Flashover

Composed of at least one inlet opening, one exhaust opening, and the connecting volume between the openings. The direction of the flow is determined by difference in pressure. Heat and smoke in a high-pressure area will flow toward areas of lower pressure.

Flow path

Molecular fragments that are highly reactive.

Free radicals

A material that will maintain combustion under specified environmental conditions. (NFPA® 921)

Fuel

A fire with adequate oxygen in which the heat release rate and growth rate are determined by the characteristics of the fuel, such as quantity and geometry. (NFPA® 921)

Fuel controlled

The total quantity of combustible contents of a building, space, or fire area, including interior finish and trim, expressed in heat units of the equivalent weight in wood

Fuel load

A form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state. (NFPA® 921)

Heat

The measure of the rate of heat transfer to a surface, expressed in kilowatts/m2, kilojoules/m2 sec, or Btu/ft2 sec. (NFPA® 921)

Heat flux

Total amount of thermal energy (heat) that could be generated by the combustion (oxidation) reaction if a fuel were completely burned. The heat of combustion is measured in British Thermal Units (Btu) per pound or Megajoules per kilogram

Heat of combustion

Total amount of heat released per unit time. The HRR is measured in kilowatts (kW) and megawatts (MW) of output.

Heat release rate

Petroleum-based organic compound that contains only hydrogen and carbon

Hydrocarbon fuel

Colorless, toxic, and flammable liquid until it reaches 79° F (26° C). Above that temperature, it becomes a gas with a faint odor similar to bitter almonds; produced by the combustion of nitrogen-bearing substances

Hydrogen cyanide (HCN)

The process of initiating self-sustained combustion. (NFPA® 921)

Ignition

First stage of the burning process in a compartment in which the substance being oxidized is producing some heat, but the heat has not spread to other substances nearby

Incipient stage

Joules are defined in terms of mechanical energy. It is equal to the energy expended in applying a force of one newton through a distance of one meter. However, it is more useful for firefighters to think about the energy required to increase temperature. 4.2 Joules are required to raise the temperature of one gram of water one degree Celsius.

Joule

The energy possessed by a body because of its motion.

Kenetic energy

Lower limit at which a flammable gas or vapor will ignite and support combustion; below this limit the gas or vapor is too lean or thin to burn (lacks the proper quantity of fuel). Also known as Lower Explosive Limit (LEL).

Lower flammable limit (LFL)

Anything that occupies space and has mass.

Matter

Materials that are capable of being mixed in all proportions

Miscible

The level at a compartment opening where the difference in pressure exerted by expansion and buoyancy of hot smoke flowing out of the opening and the inward pressure of cooler, ambient temperature air flowing in through the opening is equal.

Neutral plane

Chemical process that occurs when a substance combines with an oxidizer such as oxygen in the air; a common example is the formation of rust on metal.

Oxidation

Any material that readily yields oxygen or other oxidizing gas, or that readily reacts to promote or initiate combustion of combustible materials. (Reproduced with permission from NFPA® 400-2010, Hazardous Materials Code, Copyright�, National Fire Protection Association®)

Oxidizer

Materials that absorb heat but do not participate actively in the combustion process

Passive agent

Moment when a mixture of fuel and oxygen encounters an external heat (ignition) source with sufficient heat or thermal energy to start the combustion reaction.

Piloted ignition

The column of hot gases, flames, and smoke rising above a fire; also called convection column, thermal updraft, or thermal column. (NFPA® 921

Plume

Flammable liquids that have an attraction for water, much like a positive magnetic pole attracts a negative pole; examples include alcohol, ketone, and lacquer.

Polar solvents

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

Potential energy

Materials produced and released during burning.

Products of combustion

The chemical decomposition of a solid material by heating. Pyrolysis often precedes combustion.

Pyrolysis

Heat transfer by way of electromagnetic energy. (NFPA® 921)

Radiation

The fuel that is being oxidized or burned during combustion.

Reducing agent

A condition where the unburned fire gases that have accumulated at the top of a compartment ignite and flames propagate through the hot-gas layer or across the ceiling.

Rollover

The result of exothermic reactions, occurring spontaneously in some materials under certain conditions, whereby heat is generated at a rate sufficient to raise the temperature of the material (NFPA® 921).

Self heating

Form of fire gas ignition; the ignition of accumulated flammable products of combustion and air that are within their flammable range.

Smoke explosion

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

Solubility

Mass (weight) of a substance compared to the mass 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

Specific gravity

Initiation of combustion of a material by an internal chemical or biological reaction that has produced sufficient heat to ignite the material (NFPA® 921

Spontaneous ignition

Planned, systematic, and coordinated removal of heated air, smoke, gases or other airborne contaminants from a structure, replacing them with cooler and/or fresher air to meet the incident priorities of life safety, incident stabilization, and property conservation.

Tactical ventilation

Measure of a material's ability to transfer heat energy to other objects; the greater the energy, the higher the temperature. Measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. See Celsius Scale and Fahrenheit Scale.

Temperature

The kinetic energy associated with the random motions of the molecules of a material or object; often used interchangeably with the terms heat and heat energy. Measured in joules or Btu.

Thermal energy

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

Thermal layering

Upper limit at which a flammable gas or vapor will ignite; above this limit the gas or vapor is too rich to burn (lacks the proper quantity of oxygen). Also known as Upper Explosive Limit (UEL).

Upper flammable limit (UFL)

Buoyant layer of hot gases and smoke produced by a fire in a compartment

Upper layer

Weight of a given volume of pure vapor or gas compared to the weight of an equal volume of dry air at the same temperature and pressure. A vapor density less than 1 indicates a vapor lighter than air; a vapor density greater than 1 indicates a vapor heavier than air.

Vapor density

(1) Measure of the tendency of a substance to evaporate. (2) The pressure at which a vapor is in equilibrium with its liquid phase for a given temperature; liquids that have a greater tendency to evaporate have higher vapor pressures for a given temperature.

Vapor pressure

Physical process that changes a liquid into a gaseous state; the rate of vaporization depends on the substance involved, heat, pressure, and exposed surface area.

Vaporization

A fire with limited ventilation in which the heat release rate or growth is limited by the amount of oxygen available to the fire. (NFPA® 921)

Ventilation controlled

A unit of measure of power or rate of work equal to one joule per second (J/s).

Watt