Paper reporting forensic work on a real fire case.

This paper summarizes the essentials of an investigation conducted by the authors to test conflicting scenarios regarding the cause and origin of an accidental fire. Fire investigators proposed that an underbody fuel-leak ignited while the vehicle was in motion and transferred sufficient heat through the steel floor to cause rapid, but undetectable, ignition and fire growth in the interior of the vehicle. To assess the feasibility of the proposed scenario, a series of experiments were designed together with the development of a priori modeling studies. The transient heating across the vehicle floor was modeled, which allowed determining the characteristics for fire ignition inside the vehicle depending on the scenario studied. The post-ignition regime was studied using computational fire modeling to obtain an approximate time for smoke detection by the passengers. Results from these models provided input to the design of experimental tests with a real-scale vehicle under a forced flow imitating driving conditions. The tests showed that the only situation for which the scenario was feasible was for the condition where unexpected perforations existed in the floor pan. In the case where the floor pan did not contain perforations (as in the subject accident vehicle), heat transfer from the under-floor flame was insufficient to cause ignition of interior materials.