Preliminary Investigation of the Potential Health Risks of Nonform-Fitting Body Armor with a Focus on Female...

Body armor is an important piece of protective equipment for warfighters in battlefield environments. With more women now filling military roles, body armor designs may need to be further refined to accommodate the female anatomy instead of the male-based unisex designs. Unisex designs have been found to have negative effects on female warfighter performance, resulting in discomfort, breathing difficulty, and air gaps forming between the armor and torso. This study aimed to investigate increased injury risk because of air gaps from shock wave exposure on warfighters wearing nonform-fitting armor and the influence of material properties. Based on literature, lowered injury risk from shock exposure was determined to be associated with reduced peak pressure and impulse, and increased rise time.

An experimental approach was used to evaluate differences in energy transmission because of variations in air gap thicknesses behind targets with varying material properties. Six well-characterized materials were exposed to shock energy via free-field blasts to obtain time-pressure measurements to quantify the exposure felt by a target. Air gap thicknesses ranged from 0.0 to 2.0 cm using custom Delrin resin spacer frames. The analysis included time-pressure waveform comparison and linear regression to investigate air gap effects for each specific material.

This study found that air gap effects depend on the density of the protective plate. This was shown as the measured impulse for low-density materials exceeded the baseline (0.0-cm air gap) by an average of 165% when small air gaps were present. However, high-density materials reduced shock exposure to an average of 47.5% relative to the baseline. Similar occurrences were noted for the peak pressure. Additionally, multiple defined peak pressures occurred when small air gaps were present, likely making the exposure more harmful to warfighters despite higher peak pressures without air gaps. This is because of internal reflections at the material-target interface that trap the shock wave in a manner similar to the underwash effect in the helmet of a warfighter, causing multiple peak pressures and potentially increasing injury risk. When larger air gaps were present, the confinement of the shock wave between interfaces lessened, allowing for the energy to dissipate.

Conclusions from this study included the identification of a possible critical point for warfighter exposure to shock with air gaps between their armor and torso. This point was at a 0.5-cm air gap thickness regardless of material density, as this thickness was the most hazardous air gap size. Air gaps exceeding this thickness significantly reduced exposure, though they cannot be directly implemented into armor designs because of the increased ballistic injury risk. As the pressure exposure to the torso was shown to vary with air gap thickness, and consequently fit of the body armor, knowing the pressure externally on the body armor may not correlate to internal injuries equally for all wearers. Future work directions should investigate complex geometry armor plates to fully understand air gap injury risk effects for the wearer.