This paper describes the usage of an exponential weighting factor for appraising deceleration or force impulses registered on dummies or impacting hammers in safety testing. The proposed impulse-integration procedure, it is shown, takes into account in a more rational way, and in better conformity with published injury tolerance data, the relative importance of time and intensity of the pulse than do the "peak g" or impulse-area criteria. Use of the new Severity Index for assessment of head impact pulses is illustrated. It is shown to be of special value in comparing the relative severity of pulses which differ markedly in shape (because of structural differences in the component being struck) and it is pointed out that without a weighting factor of this nature, laboratory impact tests can yield incorrect ranking of the relative safety merit of alternative designs. Automated methods for quick calculation of the Severity Index are possible.