Fire Ignition and Origin Analysis
Fire Ignition and Origin Analysis tests whether you can determine where a fire started, what ignited it, and how to document that conclusion defensibly. The exam expects NFPA 921-style scientific method: collect data, analyze it, develop and test hypotheses, and classify the cause.
Core concepts
- Fire tetrahedron: fuel, oxygen, heat, and uninhibited chemical chain reaction.
- Origin is a location; cause is the ignition sequence (source, fuel, circumstance).
- Cause classifications: accidental, natural, incendiary, undetermined. "Undetermined" is a legitimate finding when evidence is insufficient.
- Burn patterns are indicators, not proof: V-patterns suggest vertical flame spread, char depth and alligatoring are unreliable, and "pour patterns" can result from fallen debris or ventilation.
- Arc mapping and ground-fault evidence can locate electrical activity, but must be correlated with fuel and ventilation.
Worked example
A bedroom fire shows a V-pattern above a receptacle, a tripped breaker, and arcing at the receptacle. Reasoning: the pattern and arc evidence support the receptacle as the area of origin, but origin is not cause. The investigator must identify the first fuel ignited, rule out other competent ignition sources in the area (space heater, lamp, extension cord), and test the hypothesis against witness statements and fire dynamics. If the receptacle is on an aluminum branch circuit with a known failure mode, that supports accidental electrical; if a separate accelerant pour is found, the hypothesis changes.
Traps
- Declaring cause from origin alone.
- Treating char depth or alligatoring as a reliable time/temperature indicator.
- "Negative corpus"-naming an unknown electrical fault because no other cause was found.
- Skipping evidence preservation and chain of custody.