Head impacts in animal and human cadaver tests and in aircraft accidents were simulated using finite element brain models. Brain injury severity was found to correlate with peak intracranial pressure, with serious and fatal injuries occurring when the pressures exceeded 34 psi. Using this value as the maximum allowable brain stress, tolerance curves are presented for frontal and occipital impacts which represent four head acceleration pulse shapes and impact durations between 1 and 10 msec. The brain pressure tolerance (BPT) curves are compared with other head injury criteria: Wayne State tolerance (WST) curve; Vienna Inst. of Tech. model; Hwy. Safety Res. Inst. maximum strain criterion (MSC); the Gadd Severity Index (GSI) and a modified version, Head Injury Criterion (HIC); and Federal Motor Vehicle Safety Standard 218. While the BPT curves are based entirely on brain injury data associated with impact, the WST, Vienna model, and MSC all use skull brain injury, and the GSI and HCI are based primarily on whole body accelerations usually greater than 20 msec. Protection based on these other indices would be inadequate for short duration (less than 3 msec.) impacts (such as when the head strikes an ineffectively padded or unpadded rigid surface). Ideally, tolerance curves for each kind of head injury should be superimposed, and the lowest curves used to define an overall head injury tolerance.
Abstract