R. Scott King, BSME ::::
Case Synopsis: Typically, vehicular fire investigations include evaluating the physical evidence left as a result of the incident; vehicle service, maintenance, and usage data; witness statements; fire, police, and other first-responders reports, and other relevant information. Video footage can also provide important details to assist with incident chronology and origin area. However, during a recent investigation, information from the vehicle’s Event Data Recorder (EDR) provided valuable data describing how and why the commercial motor coach caught fire.
Engineering Analysis: While traveling on a snow-covered roadway, a commercial motor coach slid harmlessly off the road’s surface and partially into a culvert. The coach became stuck and required towing. After safely offloading the passengers onto another coach, the tow truck and coach operators began working together to move the coach back on the road. While doing so, the coach caught fire leaving fire investigators wondering what happened.
Potential theories of causation included something the tow operator may have done improperly while making the physical connection to the coach, or perhaps that the coach sustained damage upon sliding into the culvert. The investigation evaluated the typical elements such as physical evidence and witness statements. Visual examination revealed that the vehicle’s electrical system was badly damaged; however, the coach’s Engine Control Module (ECM) was still intact. Aware of its data recording capabilities, engineers working for the towing company removed the device from the vehicle, utilized a remote ECM programming station, and imaged the data from within the module.
Result: The ECM was capable of recording three “events”: two Hard Brake events and one Last Stop record. Imaging the ECM revealed that all events stored within the ECM occurred in very quick succession, and all on the date and time of the reported fire. A detailed engineering evaluation of the data signature of each event revealed that the motor coach’s drive tires were “spinning” because the coach operator had repeatedly accelerated the engine by depressing the accelerator pedal. The data indicated that the tires were spinning at a high speed for at least 3 minutes. This data, along with the other available evidence, allowed investigators to conclude that the fire occurred because the rear drive tires overheated and ignited, thus allowing both parties to evaluate potential liability.
(please contact Scott King at rsk@forensicDJS.com)Categories: Case Studies