Evaluation of the biofidelity of FMVSS No. 218 injury criteria.

Objective: The biofidelity of the injury criteria used by Federal Motor Vehicle Safety Standards (FMVSS) No. 218 was examined against biomechanically based injury metrics.

Methods: An experimental method was developed to measure the helmet contact pressure distribution on a headform during an impact attenuation test. The headform pressure data from eighty impact tests to the front, crown, and side of a helmet were used in finite element model simulations to predict skull fracture. Using headform acceleration data as inputs, the Simulated Injury Monitor software package (SIMon) was used to predict brain injuries for concussion, brain contusion, and subdural hematoma.

Results: It was found that FMVSS No. 218 headform peak acceleration is the best correlate with injury metrics. Dwell times over 150 and 200 g both had poor correlation with injury metrics. The failure probability for skull fracture agrees with published results at similar linear accelerations. Concussion results were inconclusive.

Conclusions: This research has shown that peak head acceleration can be an acceptable injury metric for the FMVSS No. 218 test method. However, the current 400 g allows for a high probability of head injury. An adjusted linear head acceleration limit of 210 g predicts a 15 percent skull fracture probability. The FMVSS No. 218 test method is adequate for predicting skull fracture based on peak head acceleration limits. However, due to the use of the rigid head/neck assembly that restricts rotation, the test method is likely inadequate for predicting brain injuries.