Influence of Impact Location and Incident Angle on Thoracic Injury Risk from Kinetic Impact Projectiles

Abstract Kinetic impact projectiles (KIPs) are widely utilized in law enforcement as a non-lethal means for crowd control, yet they remain capable of causing severe or fatal injuries. This study utilizes the Total Human Model for Safety (THUMS) finite element model to evaluate thoracic injury risk across various impact locations and incident angles for two types of KIPs: the Flash-Ball and the 40 mm Sponge Round. The Viscous Criterion (VCmax) was used to assess the injury risk with a threshold of 0.8 m/s representing a 50% probability of sustaining a thoracic injury of Abbreviated Injury Scale (AIS) 2 or 3. Simulations demonstrated that impact location and incident angle influence injury severity, with near-perpendicular impacts yielding the highest VCmax values. Results indicated that due to its more concentrated frontal profile, the Sponge Round projectile transfers approximately 77% of its initial kinetic energy to the body, whereas the Flash-Ball projectile distributes force more widely, transferring 60% of its initial kinetic energy. Critically, both projectiles approached or exceeded the 0.8 m/s injury threshold at recommended minimum firing distances, particularly when impacting regions directly over the heart and lungs. The Sponge Round projectile, in particular, presented up to an 80% probability of AIS 2-3 injury under standard operational conditions. These findings suggest that current KIP designs and thoracic targeting protocols pose a substantial risk of severe injury, highlighting the urgent need for safer projectile designs and improved training to minimize unintended fatalities during deployment.