The “independent burning theory” is generally adopted in arson cases involving buildings, and the crime is considered complete when a part of the building has burned continuously. On the other hand, this is a theory within the field of jurisprudence and is not based on a scientific definition. In this study, we focused on flooring materials as burned building materials in arson cases, and conducted cone calorimeter tests on four types of wooden floorboards to investigate their ignition characteristics and burning rate. We also observed the interior of the floorboards burned by heat flux using an X-ray computed tomography (CT) system. When gasoline was spilled on the floor, the floorboards were ignited by the gasoline flame, and the maximum burning rate was found to be 1.25 to 3.26 mm per minute. From the results of cone calorimeter tests and gasoline burning experiments in a real-scale building, we predicted the maximum possible burn damage depth to floorboards caused by the thermal effects of a gasoline flame in an arson with gasoline. Based on the experimental results, we proposed a method to prove independent burning through the observation of floorboard burnout. Burn damages of the floorboards collected from locations where no continued burning after gasoline burnout was observed in the real-scale burning experiments were limited to the surface layer, below the maximum possible burn damage depth in all cases. On the other hand, the burn damage of some of floorboard sampled from locations where continued combustion was observed independent of the gasoline flame in the combustion experiments exceeded the depth. Therefore, it was validated that it is possible to determine whether the flooring burned independently of the gasoline flame by X-ray CT observation of the burn depth of the floorboard after the fire. The proposed method in this study can contribute to establishing independent combustion of a part of a building during arson using liquid fuel.
Okamoto et al. (Thu,) studied this question.