Fire Chemistry Fundamentals
Fire requires three elements—fuel, heat, and oxygen (the fire triangle)—sustained by a self-perpetuating chemical chain reaction. Arson investigators must distinguish between accidental fires (electrical faults, unattended cooking, spontaneous combustion of oily rags) and intentionally set fires. Indicators of arson include multiple points of origin (a fire that starts in two unconnected rooms simultaneously), use of ignitable liquids (gasoline, kerosene, lighter fluid) to accelerate spread, evidence of forced entry, disabled fire protection systems (disconnected alarms, blocked exits), and financial or personal motive. However, many previously accepted 'indicators' (pour patterns, crazed glass, V-patterns) have been shown by research to occur in both accidental and intentional fires—highlighting the importance of laboratory chemical analysis over pattern interpretation alone.