Injury criteria limitations
The measure of head injury potential traditionally used in dummy testing is called HIC (head injury criteria). HIC involves integrating the measured head accelerations over a particular time period, and was originally developed to correspond with likelihood of skull fracture from direct loading (Versace 1971). Injury threshold values for HIC were scaled for children from adult data (Irwin and Mertz 1997).
While HIC seems to work reasonably to predict head injury from head strike, high HIC values can also arise from the dummy’s head moving rapidly during deceleration without contacting anything. Since the main pediatric head injury mechanism of direct contact with vehicle interior components is not simulated with the FMVSS 213 test fixture, the use of HIC as a measure during FMVSS 213 testing may be somewhat flawed. Head excursion, which is also evaluated during FMVSS 213 testing, is likely a better predictor of head injury potential, in that the further forward the head travels during loading, the more likely it will strike a vehicle interior component (even if that vehicle interior is not represented on the FMVSS 213 test buck.) Head injury from vehicle interior contact is the most common mechanism of pediatric head injury in crashes (Bohman et al. 2011). Nance et al. (2010)studied factors associated with clinically significant head injury and their findings for impact type and vehicle size suggest head contact as a mechanism.
FMVSS 213 also places limits on the allowable thoracic loading based on the measured chest acceleration. However, serious chest injuries in the absence of significant intrusion are also relatively rare in field data.