Unusual post-crash firings of motor scooter: results of the forensic technical investigation by accident reconstruction

From the preliminary results of the motor scooter post-crash firing case, first presented at the ICEFA IV in Cambridge (UK) in June 2010, new technical investigations have been performed clarifying the reasons behind the unusual crash-firing accident. As stated in the first presentation, this particular scooter model has a unique frame-gas tank system. Specifically the fuel tank is ‘protected’ inside a type of half-duplex cradle frame (fig.1). When subjected to a front collision impact with a rigid ‘barrier’ (i.e. the rear wheel of an automobile - fig.2), at impact the frame of the motor scooter can, under certain situations, cause the fuel tank collapse. This phenomena occurred in both real cases examined: when the fuel tank collapsed, fuel and fuel vapours sprayed onto the two drivers arms and legs and caught on fire causing severe burning of their clothing and, consequently, their skin. Based on the preliminary conclusions on the accident reconstruction, additional tests were conducted. The objective was to further understand what contributing causes produced the tank failure and result in the projection of fuel, as had occurred in the two acknowledged cases. The potentiality of such an event occurring again had to be evaluated. A devised crash test campaign was performed to reproduce the conditions of the accident. The tests revealed that when the rear section of the scooter frame collapsed, the compression exerted by the reduction of volume resulted in the fuel spilling out of the tank. The system design of frame plus tank adopted by the manufacturer was shown not to be a safe enough solution to prevent these types of accidents from happening again. While the statistics for this type of accident may be low, the high probability of injuries from this type of accident should be carefully evaluated from a forensic point of view.