Biophysical Assessment and Predicted Thermophysiologic Effects of Body Armor

INTRODUCTION: Military personnel are often required to wear ballistic protection in order to defend against enemies. However, this added protection increases mass carried and imposes additional thermal burden on the individual. Body armor (BA) is known to reduce combat casualties, but the effects of BA mass and insulation on the physical performance of soldiers are less well documented. Until recently, the emphasis has been increasing personal protection, with little consideration of the adverse impacts on human performance. OBJECTIVE: The purpose of this work was to use sweating thermal manikin and mathematical modeling techniques to quantify the tradeoff between increased BA protection, the accompanying mass, and thermal effects on human performance. METHODS: Using a sweating thermal manikin, total insulation (I(T), clo) and vapor permeability indexes (i(m)) were measured for a baseline clothing ensemble with and without one of seven increasingly protective U.S. Army BA configurations. Using mathematical modeling, predictions were made of thermal impact on humans wearing each configuration while working in hot/dry (desert), hot/humid (jungle), and temperate environmental conditions. RESULTS: In nearly still air (0.4 m/s), IT ranged from 1.57 to 1.63 clo and i(m) from 0.35 to 0.42 for the seven BA conditions, compared to I(T) and i(m) values of 1.37 clo and 0.45 respectively, for the baseline condition (no BA). CONCLUSION: Biophysical assessments and predictive modeling show a quantifiable relationship exists among increased protection and increased thermal burden and decreased work capacity. This approach enables quantitative analysis of the tradeoffs between ballistic protection, thermal-work strain, and physical work performance.