NFPA 921

The definitions contained in this chapter apply to the terms used in this guide.

Where terms are not defined in this chapter or within another chapter, they should be defined using their ordinarily accepted meanings within the context in which they are used.

Merriam-Webster’s Collegiate Dictionary, current edition, is the source for the ordinarily accepted meaning.

Acceptable to the authority having jurisdiction.

A standard that is an extensive compilation of provisions covering broad subject matter or that is suitable for adoption into law independently of other codes and standards.

A document that is advisory or informative in nature and that contains only nonmandatory provisions. A guide may contain mandatory statements such as when a guide can be used, but the document as a whole is not suitable for adoption into law.

A document that is similar in content and structure to a code or standard but that contains only nonmandatory provisions using the word “should” to indicate recommendations in the body of the text.

An NFPA Standard, the main text of which contains only mandatory provisions using the word “shall” to indicate requirements and that is in a form generally suitable for mandatory reference by another standard or code or for adoption into law. Nonmandatory provisions are not to be considered a part of the requirements of a standard and shall be located in an appendix, annex, footnote, informational note, or other means as permitted in the NFPA Manual of Style. When used in a generic sense, such as in the phrase “standards development process” or “standards development activities,” the term “standards” includes all NFPA Standards, including Codes, Standards, Recommended Practices, and Guides.

A temperature measured in Kelvins (K) or Rankines (R).

A fuel or oxidizer, often an ignitible liquid, intentionally used to initiate a fire or increase the rate of growth or spread of fire.

An unplanned event that interrupts an activity and sometimes causes injury or damage or a chance occurrence arising from unknown causes; an unexpected happening due to carelessness, ignorance, and the like.

A system that uses moving mechanical or electrical parts to perform an action to achieve a fire protection goal, including fire detection, fire alarm, and fire suppression systems.

Someone’s or something’s surroundings, especially as they pertain to the local environment; for example, ambient air and ambient temperature.

The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. [70, 2023]

The unit of electric current that is equivalent to a flow of one coulomb per second; one coulomb is defined as 6.24 × 10¹⁸ electrons.

A high-temperature luminous electric discharge across a gap or through a medium such as charred insulation.

The diagram created as a result of an arc survey used to document the locations of arc sites on an electrical system to aid in the determination of fire origin or spread.

Melting of conductors and conducting surfaces as a result of electrical arcing. The characteristics of arc melting are described in 6.6.6.3.

The location on a conductor with localized damage that resulted from an electrical arc.

The examination of an electrical system for the presence of arc sites.

Arcing associated with a matrix of charred material (e.g., charred conductor insulation) that acts as a semiconductive medium.

A structure, part of a structure, or general geographic location within a fire scene, in which the point of origin of a fire or explosion is reasonably believed to be located. (See also 3.3.153, Point of Origin.)

A fire pattern displayed on the cross-section of a burned wooden structural member.

The definition of the crime of arson varies by jurisdiction; however, it is generally defined as the crime of maliciously and intentionally, or recklessly, starting a fire or causing an explosion. (See 12.5.6.1.)

Initiation of combustion by heat but without a spark or flame.

The lowest temperature at which a combustible material ignites in air without a spark or flame.

A deflagration resulting from the sudden introduction of air into a confined space containing oxygen-deficient products of incomplete combustion.

A rounded mass of resolidified metal on the remains of an electrical conductor or conductors that was caused by arcing and is characterized by a sharp line of demarcation between the melted and unmelted conductor surfaces.

The expanding leading edge of an explosion reaction that separates a major difference in pressure between normal ambient pressure ahead of the front and potentially damaging high pressure at and behind the front.

An acronym for boiling liquid expanding vapor explosion.

The permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.

The quantity of heat required to raise the temperature of one pound of water 1°F at the pressure of 1 atmosphere and temperature of 60°F; a British thermal unit is equal to 1055 joules, 1.055 kilojoules, and 252.15 calories.

See 3.3.113, Heat Release Rate (HRR).

A fire effect realized in gypsum products, including gypsum board, as a result of exposure to heat that drives off free and chemically bound water.

The amount of heat necessary to raise 1 gram of water 1°C at the pressure of 1 atmosphere and temperature of 15°C; a calorie is 4.184 joules, and there are 252.15 calories in a British thermal unit (Btu).

The circumstances, conditions, or agencies that brought about or resulted in the fire or explosion incident, damage to property, bodily injury, or loss of life.

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.

Carbonaceous material that has been burned or pyrolyzed and has a blackened appearance.

Convex segments of carbonized material separated by cracks or crevasses that form on the surface of char, forming on materials such as wood as the result of pyrolysis or burning.

An electrical system component that protects against faults, such as circuit breakers, fuses, arc fault circuit interrupting (AFCI) devices, and ground fault circuit interrupting (GFCI) devices.

A distinct and visible fire effect generally apparent on noncombustible surfaces after combustible layer(s) (such as soot, paint, and paper) have been burned away.

Capable of undergoing combustion.

An instrument that samples air and indicates whether there are ignitible vapors or gases present.

Any liquid that has a closed-cup flash point at or above 37.8°C (100°F). (See also 3.3.92, Flammable 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.

The heat, gases, volatilized liquids and solids, particulate matter, and ash generated by combustion.

An ignition source that has sufficient energy and is capable of transferring that energy to the fuel long enough to raise the fuel to its ignition temperature. (See 19.4.2.)

Heat transfer to another body or within a body by direct contact.

Heat transfer by circulation within a medium such as a gas or a liquid.

The tendency of a material to move or deform permanently to relieve stresses.

A flow of electric charge.

The process of systematically utilizing logical techniques to dissect, reorder, evaluate, and interpret data.

The process by which conclusions are drawn by logical inference from given premises.

Propagation of a combustion zone at a velocity that is less than the speed of sound in the unreacted medium. [68, 2023]

The mass of a substance per unit volume, usually specified at standard temperature and pressure. The density of water is approximately one gram per cubic centimeter. The density of air is approximately 1.275 grams per cubic meter.

(1) Sensing the existence of a fire, especially by a detector from one or more products of the fire, such as smoke, heat, infrared radiation, and the like. (2) The act or process of discovering and locating a fire.

Propagation of a combustion zone at a velocity greater than the speed of sound in the unreacted medium. [68, 2023]

A gas, vapor, dust, particulate, aerosol, mist, fog, or hybrid mixture of these, suspended in the atmosphere, which is capable of being ignited and propagating a flame front.

A flame in which fuel and air mix or diffuse together at the region of combustion.

The spread of fire by the dropping or falling of burning materials. Synonymous with “fall down.”

Temperatures reached in fires that produce physical effects that can be related to specific temperature ranges.

A small, incandescent particle created by some arcs.

A broad concept that includes public or private information stored in an electronic or digital medium, such as data available from computers (including email), CD-ROM discs, DVDs, Internet, cloud storage, personal digital assistants (PDAs), smart phones, tablets, GPS systems, satellites, and drones. ESI includes writings, drawings, graphs, charts, photographs, sound recordings, images, video recordings, data compilations, computer-aided design files such as blueprints or maps, metadata, equipment/process control and data logging system files, and any other data that is stored electronically.

Factual data based on actual measurement, observation, or direct sensory experience rather than on theory and capable of being verified or known to be true.

The ability to perform work. (See 5.1.2.)

The process of air or gases being drawn into a fire, plume, or jet.

A material with a pressure ratio (maximum pressure/pressure at ignition, in absolute units) equal to or greater than 2.0 in any test when tested using the explosibility or Go/No-Go screening test described in Section 13 of ASTM E1226, Standard Test Method for Explosibility of Dust Clouds. [68, 2023]

The sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure. These high-pressure gases then do mechanical work such as moving, changing, or shattering nearby materials.

Study of how chemistry, physics, fire science, engineering disciplines of fluid and solid mechanics, and heat transfer interact to influence explosion behavior.

Any chemical compound, mixture, or device that functions by explosion.

Any material that can act as fuel for an explosion.

The side of a structural assembly or object that is directly exposed to the fire.

To cause to cease burning.

Distortion, breakage, deterioration, or other fault in an item, component, system, assembly, or structure that results in unsatisfactory performance of the function for which it was designed.

A logical, systematic examination of an item, component, assembly, or structure and its place and function within a system, conducted in order to identify and analyze the probability, causes, and consequences of potential and real failures.

See 3.3.52, Drop Down.

The current delivered at a point on the system during a short-circuit condition. [70, 2023]

The time in minutes, determined under specific laboratory conditions, at which the stud or joist in contact with the exposed protective membrane in a protected combustible assembly reaches an average temperature rise of 121°C (250°F) or an individual temperature rise of 163°C (325°F) as measured behind the protective membrane nearest the fire on the plane of the wood.

A rapid oxidation process, which is an exothermic chemical reaction, resulting in the evolution of light and heat in varying intensities.

The process of determining the origin, cause, development, responsibility, and, when required, a failure analysis of a fire or explosion.

The boundary of fire effects within a scene in which the area of origin will be located. The fire area is characterized by identifying the border between damaged and undamaged areas, which are distinguishable by fire effects and patterns created by flame, heat, and smoke.

The circumstances, conditions, or agencies that bring together a fuel, ignition source, and oxidizer (such as air or oxygen) resulting in a fire or a combustion explosion.

The study of chemical processes that occur in fires including changes of state, decomposition, and combustion.

The detailed study of how chemistry, fire science, and the engineering disciplines of fluid mechanics and heat transfer interact to influence fire behavior.

The observable or measurable changes in or on a material as a result of a fire.

Any situation, process, material, or condition that can cause a fire or explosion or that can provide a ready fuel supply to augment the spread or intensity of a fire or explosion, all of which pose a threat to life or property.

The process of determining the origin, cause, and development of a fire or explosion.

An individual who has demonstrated the skills and knowledge necessary to conduct, coordinate, and complete a fire investigation. [1033, 2022]

The physical changes, or identifiable shapes, formed by a fire effect or group of fire effects.

See 3.3.85, Fire Spread.

The process of recreating the physical scene during fire scene analysis investigation or through the removal of debris and the placement of contents or structural elements in their prefire positions.

The body of knowledge concerning the study of fire and related subjects (such as combustion, flame, products of combustion, heat release, heat transfer, fire and explosion chemistry, fire and explosion dynamics, thermodynamics, kinetics, fluid mechanics, fire safety) and their interaction with people, structures, and the environment.

The movement of fire from one place to another.

The first fuel ignited is that which first sustains combustion beyond the ignition source.

A body or stream of gaseous material involved in the combustion process and emitting radiant energy at specific wavelength bands determined by the combustion chemistry of the fuel. In most cases, some portion of the emitted radiant energy is visible to the human eye. [72, 2022]

The flaming leading edge of a propagating combustion reaction zone.

The condition where unburned fuel (pyrolysate) from the originating fire has accumulated in the upper layer to a sufficient concentration (i.e., at or above the lower flammable limit) that it ignites and burns. This can occur without ignition of, or prior to the ignition of, other fuels separate from the origin.

Capable of burning with a flame.

The upper or lower concentration limit at a specified temperature and pressure of a flammable gas or a vapor of an ignitible liquid and air, expressed as a percentage of fuel by volume that can be ignited.

A liquid that has a closed-cup flash point that is below 37.8°C (100°F) and a maximum vapor pressure of 2068 mm Hg (40 psia) at 37.8°C (100°F). (See also 3.3.36, Combustible Liquid.)

The range of concentrations between the lower and upper flammable limits. [68, 2023]

A fire that spreads by means of a flame front rapidly through a diffuse fuel, such as dust, gas, or the vapors of an ignitible liquid, without the production of damaging pressure.

The lowest temperature of a liquid, as determined by specific laboratory tests, at which the liquid gives off vapors at a sufficient rate to support a momentary flame across its surface.

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, given sufficient availability of oxygen, fire spreads rapidly throughout the space, resulting in full room involvement or total involvement of the compartment or enclosed space.

The application of science to answer questions of interest to the legal system.

A material that will maintain combustion under specified environmental conditions. [53, 2021]

Natural gas, manufactured gas, LP-Gas, and similar gases commonly used for commercial or residential purposes such as heating, cooling, or cooking.

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

A fire in which the heat release rate and growth rate are controlled by the characteristics of the fuel, such as quantity and geometry, and in which adequate air for combustion is available.

Condition in a compartment fire in which the entire volume is involved in combustion of varying intensities.

The physical state of a substance that has no shape or volume of its own and will expand to take the shape and volume of the container or enclosure it occupies.

Luminous burning of solid material without a visible flame.

A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and earth or to some conducting body that serves in place of the earth.

A current that flows outside the normal circuit path, such as (1) through the equipment grounding conductor; (2) through conductive material in contact with lower potential (such as earth), other than the electrical system ground (metal water or plumbing pipes, etc.); or (3) through a combination of these ground return paths.

A condition that presents the potential for harm or damage to people, property, or the environment.

A substance (solid, liquid, or gas) that when released is capable of creating harm to people, the environment, and property.

A form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state.

An arrow used in a fire scene drawing to show the direction of heat, smoke, or flame flow.

The measure of the rate of heat transfer to a surface or an area, typically expressed in kW/m², or W/cm².

The heat energy that brings about ignition.

The rate at which heat energy is generated by burning.

The exchange of thermal energy between materials through conduction, convection, and/or radiation.

A material that is capable of sustaining a reaction front that moves through the unreacted material at a speed equal to or greater than that of sound in that medium [typically 1000 m/sec (3000 ft/sec)]; a material capable of sustaining a detonation. (See also 3.3.49, Detonation.)

A rapid pressure rise or high-force explosion characterized by a shattering effect on the confining structure or container and long missile distances.

An explosible heterogeneous mixture, comprising gas with suspended solid or liquid particulates, in which the total flammable gas concentration is ≥10 percent of the lower flammable limit (LFL) and the total suspended particulate concentration is ≥10 percent of the minimum explosible concentration (MEC). [68, 2023]

Any substance that will spontaneously ignite or explode upon exposure to an oxidizer.

Any combustible or flammable liquid.

The process of initiating self-sustained combustion.

The quantity of heat energy that should be absorbed by a substance to ignite and burn.

Minimum temperature a substance should attain in order to ignite under specific test conditions.

The time between the application of an ignition source to a material and the onset of self-sustained combustion.

A fire that is intentionally ignited in an area or under circumstances where and when there should not be a fire.

The process by which a person starts from a particular experience and proceeds to generalizations. The process by which hypotheses are developed based upon observable or known facts and the training, experience, knowledge, and expertise of the observer.

Any person, entity, or organization, including their representatives, with statutory obligations or whose legal rights or interests may be affected by the investigation of a specific incident.

A group of individuals working on behalf of an interested party to conduct an investigation into the incident.

A line on a diagram connecting points of equal char depth.

The preferred SI unit of heat, energy, or work. A joule is the heat produced when one ampere is passed through a resistance of one ohm for one second, or it is the work required to move a distance of one meter against a force of one newton. There are 4.184 joules in a calorie, and 1055 joules in a British thermal unit (Btu). A watt is a joule/second. [See also 3.3.24, British Thermal Unit (Btu), and 3.3.27, Calorie.]

A measurement of energy release rate.

See 3.3.122, Ignition Temperature.

The systematic process of removing debris from the top down and observing the relative location of artifacts at the fire scene.

The borders defining the differences in fire effects on materials between the affected area and adjacent, less-affected areas.

An explosive that has a reaction velocity of less than 1000 m/sec (3000 ft/sec).

A slow rate of pressure rise or low-force explosion characterized by a pushing or dislodging effect on the confining structure or container and by short missile distances.

The fuel that is first set on fire by the heat of ignition; to be meaningful, both a type of material and a form of material should be identified.

The minimum concentration of a combustible dust cloud that is capable of propagating a deflagration through a uniform mixture of the dust and air under the specified conditions of test. [68, 2023]

The lowest capacitive spark energy capable of igniting the most ignition-sensitive concentration of a flammable vapor-air mixture or a combustible dust-air mixture as determined by a standard test procedure. [652, 2019]

A material that, in the form in which it is used and under the condition anticipated, will not ignite, burn, support combustion, or release flammable vapors when subjected to fire or heat.

(1) Not readily capable of burning with a flame. (2) Not liable to ignite and burn when exposed to flame. Its antonym is flammable.

Data from sources other than those collected from the scene of a fire or explosion incident.

The SI unit of electrical impedance or, in the direct current case, electrical resistance.

Any device that emits a flame that is exposed to outside elements.

The general location where a fire or explosion began. (See 3.3.153, Point of Origin, or 3.3.14, Area of Origin.)

Any current in excess of the rated current of equipment or the ampacity of a conductor; it may result from an overload (see 3.3.147), short circuit (3.3.179), or ground fault (3.3.106).

A firefighting term involving the process of final extinguishment after the main body of the fire has been knocked down. All traces of fire must be extinguished at this time.

Operation of equipment in excess of normal, full-load rating or of a conductor in excess of rated ampacity that, where it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload.

Insufficiency of oxygen to support combustion. (See also 3.3.211, Ventilation-Controlled Fire.)

Any component of a building or structure that provides protection from fire or smoke without any type of system activation or movement. [3, 2024]

See 3.3.122, Ignition Temperature.

Any of a wide range of natural or synthetic organic materials of high molecular weight that can be formed by pressure, heat, extrusion, and other methods into desired shapes.

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

The physical location within the area of origin where a heat source, a fuel, and an oxidizing agent first interact, resulting in a fire or explosion.

A property of a process, such as fire, which describes the amount of energy that is emitted, transferred, or received per unit time and is measured in joules per second (J/s) or watts (W).

A flame for which the fuel and oxidizer are mixed prior to combustion, as in a laboratory Bunsen burner or a gas cooking range; propagation of the flame is governed by the interaction between flow rate, transport processes, and chemical reaction.

Application or use of measures to prevent damage, change or alteration, or deterioration.

Print data includes writings, drawings, graphs, charts, photographs, images, and other material in paper or print form, including ESI that has been reproduced on paper or print media.

See 3.3.38, Combustion Products.

A description of the specific procedures and methodologies by which a task or tasks are to be accomplished.

The cause that directly produces the effect without the intervention of any other cause.

Product of decomposition through heat; a product of a chemical change caused by heating.

A process in which material is decomposed, or broken down, into simpler molecular compounds by the effects of heat alone; pyrolysis often precedes combustion.

Any substance that spontaneously ignites upon exposure to atmospheric oxygen.

Electromagnetic transmission of heat energy; increases the sensible temperature of any substance capable of absorbing the radiation, especially solid and opaque objects.

Heat transfer by way of electromagnetic waves that are longer than visible light waves and shorter than radio waves.

A return to flaming combustion after apparent but incomplete extinguishment.

The accountability of a person or other entity for the event or sequence of events that caused the fire or explosion, spread of the fire, bodily injuries, loss of life, or property damage.

The degree of peril; the possible harm that might occur that is represented by the statistical probability or quantitative estimate of the frequency or severity of injury or loss.

See 3.3.89, Flameover.

The general physical location of a fire or explosion incident (geographic area, structure or portion of a structure, vehicle, vessel, piece of equipment, etc.) designated as important to the investigation because it may contain physical damage or debris, evidence, victims, or incident-related hazards.

The systematic pursuit of knowledge involving the recognition and definition of a problem; the collection of data through observation and experimentation; analysis of the data; the formulation, evaluation and testing of hypotheses; and, where possible, the selection of a final hypothesis.

A craterlike indentation created at the point of origin of some explosions.

An explosion with a highly localized point of origin, such as a crater.

Any subsequent explosion resulting from an initial explosion.

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.

Ignition resulting from self-heating, synonymous with spontaneous ignition.

The minimum temperature at which the self-heating properties of a material lead to ignition.

An arc site where one or more of the circuit conductors were physically severed by the arcing event at that location.

An abnormal connection (including an arc) of relatively low impedance, whether made accidentally or intentionally, between two or more points of different potential. [70, 2023]

The general physical location of the incident, including the scene and the surrounding area deemed significant to the process of the investigation and support areas.

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. [318, 2022]

The condensed residue of suspended vapors and liquid products of incomplete combustion.

See 3.3.19, Backdraft.

Self-sustained glowing combustion without flame, usually with incandescence and smoke.

Black particles of carbon produced in a flame.

Chipping or pitting of concrete or masonry surfaces.

A moving particle of solid material that emits radiant energy due either to its temperature or the process of combustion on its surface. [654, 2020]

The ratio of the average molecular weight of a gas or vapor to the average molecular weight of air, or the ratio of the density of a gas to the density of dry air at standard temperature and pressure.

The ratio of the mass of a given volume of a substance to the mass of an equal volume of water at a temperature of 4°C.

Loss, destruction, or material alteration of an object or document that is evidence or potential evidence in a legal proceeding by one who has the responsibility for its preservation.

Process whereby a material increases in temperature without drawing heat from its surroundings.

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

The sum of all the work done to extinguish a fire, beginning at the time of its discovery.

A fuel that is subject to ignition by thermal radiation such as from a flame or a hot gas layer.

The degree of sensible heat of a body as measured by a thermometer or similar instrument.

See 3.3.152, Plume.

The increase in length, volume, or surface area of a body with rise in temperature.

The properties of a material that characterize its rate of surface temperature rise when exposed to heat; related to the product of the material’s thermal conductivity (k), its density (ρ), and its heat capacity (c).

The branch of physics that deals with the relationship between heat and other forms of energy.

The study of the science, methodology, and practice of temperature measurement.

Plastic materials that soften and melt under exposure to heat and can reach a flowable state.

Plastic materials that are hardened into a permanent shape in the manufacturing process and are not commonly subject to softening when heated; typically form char in a fire.

Graphic representation of the events in a fire incident displayed in chronological order.

A fire scene where a fire continued to burn until most combustibles were consumed and the fire self-extinguished due to a lack of fuel or was extinguished when the fuel load was reduced by burning and there was sufficient suppression agent application to extinguish the fire.

Solid or liquid fuel used to intentionally spread or accelerate the spread of a fire from one area to another.

A written or oral consensus between the interested parties concerning the management of the investigations.

A buoyant layer of hot gases and smoke produced by a fire in a compartment.

The gas phase of a substance, particularly of those that are normally liquids or solids at ordinary temperatures. (See also 3.3.103, Gas.)

An opening for the passage of, or dissipation of, fluids, such as gases, fumes, smoke, and the like.

The movement of gases within, into, or from any compartment or space or the firefighting operation of removing smoke and heat from the structure by opening windows and doors or making holes in the roof.

A fire in which the heat release rate or growth is controlled by the amount of air available to the fire.

The escape of smoke and heat through openings in a building.

The unit of electrical pressure (electromotive force) represented by the symbol “E”; the difference in potential required to make a current of one ampere flow through a resistance of one ohm.

Unit of power, or rate of work, equal to one joule per second, or the rate of work represented by a current of one ampere under the potential of one volt.

An outline of the tasks to be completed as part of the investigation including the order or time line for completion. See Chapter 15, Planning the Investigation.

A canine-handler team is a human and working dog who train and work together as an operational unit. [SC1, 2011]

Certification is the recognition that a canine-handler team has acquired and demonstrated specialized knowledge, skills, and abilities in the standard practices necessary to execute the duties of a canine team. Certification also provides the fire investigator a means of identifying those canine-handler teams that have successfully demonstrated compliance with established requirements. In addition, certification establishes that a canine-handler team achieves and maintains proficiency.

The handler is a person who has successfully completed a documented training and certification process in canine handling in the specific discipline of ignitible liquid canine detection and maintains those abilities through field application, maintenance training, scheduled recertification, and continuing education. (See 3.4.2, Certification.) [SC1, 2011]

Ignitible liquid detection canines (IGL canines) are dogs specifically trained to locate and respond to the presence of certain classes of ignitible liquids by associated odor.

Operational usage: A dog’s olfactory ability to distinguish between various odors.

Fire characterized by rapid fire spread with higher intensity, normally burning with the wind or up slope—also known as a forward fire or a run.

Those flammable materials located from approximately 2 m (6 ft) above the surface to the crowns of the canopy, and which can include tree branches, leaves, needles, snags, moss, and tall brush.

A fire spreading against the wind or downslope.

A fire that advances from top to top of trees or shrubs more or less independent of a surface fire—also classed as passive, active, or independent to distinguish the degree of independence from a surface fire.

The layer of decomposing organic materials lying below the litter layer of freshly fallen twigs, needles, and leaves and immediately above the mineral soil.

See 3.5.7, Firebrand.

Flaming or glowing fuel particles that can be carried naturally by wind, convection currents, or by gravity into unburned fuels.

The portion of a fire moving most rapidly.

The larger area where the fire first established itself and is identified by an analysis of the fire behavior context, macroscale fire pattern indicators, and witness statements.

All flammable materials located between the mineral soil layer and the ground surface, which typically include twig, leaf, and needle litter and decomposing vegetation such as duff, peat moss, buried limbs, and roots.

The opposite end of the fire from the head.

The smallest area that a wildfire investigator can define based on the physical evidence of the fire pattern indicators, within the specific origin area, in which a competent ignition source came into contact with the first fuel ignited.

Rate or spread and intensity of a fire usually falling somewhere in between advancing and backing with spread lateral to the main direction of fire travel—also known as a flanking fire.

The smaller area within the general origin area where the fire’s direction of spread was first influenced by fuel, weather, or topography.

Ignitable materials located from the surface of the ground to approximately 2 m (6 ft) above the surface, which includes grasses, leaves, twigs, needles, field crops, slash, and downed limbs.

Where random or erratic fire travel transitions to fire effects causing patterns to indicate a directional spread of fire, which may be lateral, advancing, or backing.

An event dealing with a fire in the wildland; originating from an unplanned ignition, such as lightning, volcanos, unauthorized and accidental human-caused fires, and prescribed fires that are declared wildfires.

An area in which development is essentially nonexistent, except for roads, railroads, powerlines, and similar transportation facilities and where structures, if any, are widely scattered.