SPH-4 helmet damage and head injury correlation.

Human tolerance to head impact was assessed by correlating the force levels required to duplicate damage seen in 14 SPH-4 aviator helmets retrieved from U.S. Army helicopter crashes with resulting head injury. Head injury occurred at peak acceleration levels far below 400 G, which is the value currently used by the U.S. Army as the pass-fail criterion in evaluating the impact attenuation performance of prospective aircrew helmets. Concussive head injuries occurred below Severity Index values of 1500 and below Head Injury Criterion values of 1000. These are considered concussive threshold values by the National Operating Committee on Standards for Athletic Equipment and by the Department of Transportation, respectively. Because peak transmitted force was the best estimator of the Abbreviated Injury Scale values assigned to the 14 cases, it may be a more effective criterion to use in the evaluation of helmet impact attenuation performance than is peak G, Severity Index, or Head Injury Criterion.