CFI (FAA) key terms

The rapid transition from a growing fire to one where flames fill a compartment and all exposed combustible surfaces ignite nearly at once, usually driven by high heat flux and accumulated hot gases.

Chemical decomposition of a solid fuel caused by heat, producing combustible gases and char before visible flaming occurs; it does not require oxygen and can precede ignition.

Slow, low-temperature combustion without flame, often at the surface of porous fuels, producing smoke, char, and heat that can transition to flaming if conditions change.

The rate at which a fire releases energy, usually expressed in kilowatts or megawatts; it strongly affects fire growth, temperature, and the likelihood of flashover.

The horizontal boundary in a compartment fire where hotter upper gases and cooler lower air have roughly equal pressure, visible as the line where smoke stops descending and fresh air remains below.

A rapid deflagration caused when oxygen enters a hot, fuel-rich, underventilated compartment and ignites accumulated gases, producing a pressure wave and often forcing flames out openings.

The buoyant column of hot gases, smoke, and flames rising above burning material, entraining air and driving ceiling jets and upper-layer heating.

The division of a building into fire-resistant compartments using walls, floors, and closures so fire and smoke are delayed from spreading to adjoining spaces.

A wall, floor, door, or other building component tested and labeled to resist fire for a specified period, limiting fire and smoke spread when properly installed and maintained.

A fixed piping system with hose connections at various building levels, allowing firefighters to attach hoses and obtain water without stretching long lines from a pumper.

The vertical supply pipe that connects a building's sprinkler system to its water source and includes controlling valves, alarms, drains, and test connections.

Breaking or chipping of concrete surfaces caused by heat, moisture expansion, or rapid cooling, often exposing aggregate and reinforcing steel; it can mimic patterns of intense local burning.

The geographic space within a structure or outdoor site where a fire began, determined by analyzing fire patterns, witness accounts, and physical evidence rather than by a single clue.

The precise location within the area of origin where the first fuel ignited, identified by converging fire patterns, damage, and physical evidence.

The heat or energy source that initiates combustion, such as a flame, spark, hot surface, ember, or chemical reaction, evaluated for capacity, proximity, and timing.

The fuel item or substance initially involved in combustion; identifying it helps link the ignition source to the fire's origin and early growth.

A visible or measurable change in materials caused by fire, heat, or smoke, such as charring, melting, or staining, used to interpret fire direction and origin.

A fire cause conclusion reached by eliminating all accidental causes without reliable evidence of an intentional act; NFPA 921 treats it as an improper basis for an incendiary determination.

The category assigned to a fire's cause, commonly accidental, natural, incendiary, or undetermined, based on evidence and the scientific method rather than suspicion.

A documented, unbroken record of who collected, handled, transferred, stored, and analyzed each evidence item, supporting its integrity and admissibility in legal proceedings.

A chronological record listing each item collected at a scene, including its description, location, collector, date, and disposition, to preserve accountability and support later analysis.

A labeled object of known size placed beside evidence in photographs so viewers can judge dimensions, position, and relationships accurately.

Material collected from an unaffected or comparable area, used as a baseline for comparison with suspected fire debris or contaminated evidence during laboratory analysis.

A combustion wave that propagates below the speed of sound through a fuel-air mixture or explosive material, producing heat, gas expansion, and a pressure wave rather than a supersonic shock.

A supersonic combustion wave driven by a shock front that compresses and ignites the explosive material, producing extremely high pressures and damaging blast effects.

Boiling liquid expanding vapor explosion: a pressure vessel rupture caused when contained liquid is heated above its boiling point and the vessel fails, releasing flashing vapor and often igniting.

The pressure above normal atmospheric pressure created by a blast wave; it is measured in units such as psi or bar and causes structural damage and injuries.

The concentration range of fuel vapor or gas in air that can ignite and burn; below the lower limit the mixture is too lean, and above the upper limit too rich.

Analysis of electrical arcing damage along circuits to identify where a fire may have damaged wiring; arcs can help locate fire spread but do not by themselves prove cause.

Small rounded beads or globules formed when copper conductors melt and resolidify, sometimes indicating high-temperature electrical arcing, though fire exposure can also produce similar melting.

An unintended electrical path from a conductor to ground, which can produce sparks, heating, or shock hazards and may initiate a fire if protective devices do not clear it.

A self-accelerating heating process in a battery or chemical system where heat generation exceeds heat dissipation, potentially causing venting, fire, or explosion.

A structured witness interviewing technique that uses open-ended prompts, context reinstatement, and varied retrieval to improve accurate recall without suggesting answers.

A question that suggests the desired answer or contains information the witness has not stated, risking contaminated memory and unreliable statements.

A systematic process of observing, forming hypotheses, testing them against evidence, and revising conclusions; NFPA 921 requires this approach for fire and explosion investigations.

A proposed explanation for observed facts that must be tested against evidence; in fire investigation, competing hypotheses should be considered before a cause is determined.

A legal test for admitting expert testimony that considers whether the method is testable, peer reviewed, has known error rates, and is generally accepted in the relevant field.

The loss, alteration, or destruction of evidence that may be relevant to litigation, which can lead to sanctions, adverse inferences, or other legal consequences.

The ongoing assessment and control of hazards at an investigation site, including structural instability, utilities, chemicals, traffic, and weather, before and during scene work.

A situation where an investigator's personal, financial, or professional interests could improperly influence impartiality, requiring disclosure or withdrawal from the case.