CVFI cheat sheet

Fire tetrahedron: fuel, oxidizer, heat, and uninhibited chemical chain reaction; removing any one leg extinguishes flaming combustion.

Ignition temperature is the minimum temperature at which a fuel vapor-air mixture self-heats to ignition without an external pilot; flash point is the lowest temperature producing ignitable vapor (closed-cup test).

Flammable range for gasoline vapor in air is roughly 1.4% to 7.6% by volume; below the lower limit the mixture is too lean, above the upper limit too rich.

Heat release rate governs fire growth; a typical passenger vehicle interior reaches flashover conditions in roughly 3 to 5 minutes under a fully developed compartment fire.

Automotive materials: magnesium alloys in instrument panels and transmissions burn with a brilliant white flame; aluminum melts near 660 C and can sag or pool, leaving identifiable residue patterns.

Battery electric vehicle fires: lithium-ion thermal runaway propagates cell-to-cell, produces flammable/ toxic off-gas (including hydrogen fluoride and carbon monoxide), and can reignite hours after apparent extinguishment.

Color and melting of zinc coatings, copper wire annealing, and plastic deformation are temperature indicators; copper anneals above roughly 400 to 500 C, and spring-temper loss in steel occurs above about 600 C.

Fire patterns on vehicles include V-patterns, pour patterns, pooled fuel burning on the undercarriage, and protected areas; each is evidence of fuel location and ventilation, not proof of cause alone.

Spontaneous ignition sources in vehicles include catalytic converter surface temperatures above 400 C, turbocharger heat soak, electrical short circuits, and friction from failed bearings or brakes.

Vehicle fire origin determination follows the sequence: identify the area of greatest damage, trace to the lowest point of burning, then correlate with the fuel and ignition sources present.

Arson indicators include multiple separate origins, presence of accelerant pour patterns, foreign objects (fuses, timing devices, containers), and removal of valuables or personal items.

Accidental indicators include localized electrical arcing at a fault, fuel line failure near a heat source, and mechanical friction damage consistent with component failure.

Explosions in vehicles usually involve fuel-air mixtures in the tank or vapor space; a fuel tank explosion produces outward deformation of the tank and blast damage radiating outward.

Deflagration versus detonation: deflagration propagates below the speed of sound and produces a pressure wave; detonation propagates supersonically and produces characteristic shattering and cratering.

Post-blast indicators include pitting, cratering, metal fragmentation, and directional soot patterns; the seat of the explosion is where damage is most severe and symmetrical.

Chain of custody for vehicle evidence must be documented from recovery through laboratory analysis; photographic documentation should include overall, mid-range, and close-up views before removal.

Accelerant detection relies on laboratory analysis (headspace GC-MS); field indicators such as odor or burn patterns are presumptive only and must be confirmed by laboratory testing.

NFPA 921 defines the scientific method: identify the problem, collect data, analyze data, develop a hypothesis, test the hypothesis, and select the final hypothesis.

The methodology requires that all hypotheses be tested against the physical evidence; a hypothesis that cannot be tested or is contradicted by evidence must be discarded.

Fire cause classification: accidental, natural, incendiary, or undetermined; the investigator must not default to accidental when evidence is insufficient.

Origin determination uses fire patterns, witness observations, and physical evidence; the area of origin is the location where the fire began, and the cause is the circumstances that brought ignition source and fuel together.

NFPA 921 cautions against using a single fire pattern as proof of origin; patterns must be corroborated by multiple independent lines of evidence.

The negative corpus concept prohibits declaring a cause by eliminating all accidental causes without affirmative evidence of an incendiary cause.

Documentation requirements include photographs, diagrams, measurements, witness statements, and a written report that explains the reasoning and evidence.

The investigator must consider the possibility of a rekindle, and must distinguish between the initial fire and any subsequent fire caused by remaining heat sources.

A fire investigation report should contain: summary, scene description, evidence collected, analysis, origin determination, cause determination, and conclusion.

The report must state the cause classification (accidental, natural, incendiary, undetermined) and the basis for that classification.

Opinions in the report must be supported by evidence; the report should distinguish between observation, data, and interpretation.

Photographs and diagrams must be labeled with date, time, location, and orientation; chain-of-custody records must accompany all physical evidence.

The investigator should document all hypotheses considered, including those rejected, and explain why they were rejected.

Explosion investigations require documentation of blast damage, fragment distribution, and any chemical residue analysis; the report should address the possibility of a fuel-air explosion.

Reports must be written in clear, objective language and avoid conclusory statements unsupported by evidence; the report may be subject to peer review and legal scrutiny.

Quality assurance includes independent review of the report and evidence by a qualified second investigator before finalization.