In order to define parameters that control the design of occupant protection systems, we used a biomechanical engineering approach to injury causation. From review of 87 autopsies applied to victims of pure frontal collisions, an injury level for the brain was specified in terms of the magnitude and history of some mechanical parameters. Peak and average linear and angular accelerations, their duration and rate of onset, intra-cranial pressure and force and energy applied to the cranium have been utilized for this purpose. The design of occupant protection systems for head injury is based on lowering the deceleration rate at impact. Although protecting against focal brain injury, these lower deceleration rates and longer pulse durations may place the occupant in jeopardy of developing fatal diffuse brain injury.