Examining the Effects of Blast Orientation, Blast Intensity, and the Combat Helmet on Regional Surface Pressures in a Surrogate Human Head Model

Introduction: Military helmets primarily offer protection against ballistic or blunt trauma, but the prevalence of blast traumatic brain injuries (bTBIs) in recent conflicts have highlighted the need for improved protection against blast. According to the U.S. Department of Defense, nearly 500,000 service members have been diagnosed with a TBI since the year 2000, and reports indicate that around two-thirds of these injuries could be due to blast. The ability of current military helmets to mitigate neurotrauma from primary blast is not known, as the helmets are not designed for nor tested in blast conditions. The objective of this work was to measure surface pressures of a surrogate skull model for a range of blast intensities, in two blast orientations, with and without a military combat helmet to evaluate the effectiveness of current protective equipment in a blast environment.

Materials and

Methods: A human skull model was affixed to a Hybrid III neck and instrumented with four pressure transducers facing externally and flush with the surface of the skull. Three pressure transducers were placed along the midline, with one in the forehead, one in the top front of the head, and one in the crown of the head. The fourth pressure transducer was placed on the side of the skull above the ear. An enhanced combat helmet was instrumented with three pressure transducers also facing externally and flush with the surface. Similar to the locations of the skull pressure transducers, two transducers were placed along the midline at the top front and the crown of the head, and the third was placed above the ear. A large gas-detonation advanced blast simulator (ABS), totaling 40 ft in length with a cross-section of 4 ft by 4ft, located at Virginia Tech was used to expose the surrogate skull to blast overpressures of 16 and 24 psi with and without the combat helmet. The skull-neck complex was affixed to a stand in the middle of the ABS test section that was configured for two blast orientations: frontal with 0° rotation and 45° rotation. Three pressure transducers were mounted in the wall of the ABS to measure static overpressure in the test section. Data was sampled at 800 kHz using a TMX Multi-Channel High Speed Data Acquisition Recorder.

Results, Conclusions, and Discussions: Regardless of the blast orientation or the helmeted/unhelmeted condition, the skull surface pressures increased with increasing blast intensity. In the 0° rotation blast orientation, reductions in peak pressure are seen in the front and side locations with the helmet compared to the unhelmeted condition; however, the peak pressure is actually increased by a factor of 3 at the back of the skull with the helmet (Figure 1). In the 45° rotation blast orientation without the helmet, the peak pressures in the skull are reduced for the front and side locations but are increased in the back compared to the 0 deg orientation. With the introduction of the helmet in the 45° orientation, the peak pressures in the skull increased at all locations. These increases in peak pressure with the combat helmet are likely due to an underwash effect in which the blast wave inside the gap between the head and the helmet generates an increased pressure region often opposite the direction of the incident wave. The standard pads provided with the combat helmet appear to be insufficient for preventing the blast wave from entering the gap between the head and helmet, and as this increased pressure region can worsen bTBI, future work should investigate different pad geometries to help mitigate the underwash effect.

Acknowledgements (Optional): This work was funded in part by the Defense Health Agency with support by the Walter Reed Army Institute of Research.