Heat Strain Attenuation while Wearing NBC Clothing: Dry-Ice Vest Compared to Water Spray

Background: While wearing impermeable nuclear, biological, and chemical (NBC) clothing, reduction of thermal stress is of primary importance. We compared the effect between two cooling methods on the attenuation of heat strain. Methods: There were six male subjects who were divided into two groups of three and exposed on two consecutive days to 125 min of exercise in a high heat load (40°C, 40% RH) wearing NBC clothing. They were cooled by one of two different cooling methods: an active cooling vest (CV) based on the sublimation of dry ice, or tap water spraying (TP). Results: After 2 h, rectal temperature (Tre) was significantly higher for the CV compared with the TP (38. 1 ± 0.04°C vs. 37.7 ± 0.10°C, respectively). Skin temperature (Tsk) was significantly higher for the CV compared with the TP (36.60 ± 0.54°C vs. 34.90 ± 0.35°C, respectively). In the second hour, heart rate (HR) was significantly higher for CV compared with TP (118 ± 13 bpm vs. 104 ± 64 bpm, respectively). Heat storage was significantly higher after the first and second hours for the CV compared with the TP. The physiological strain index (PSI) was higher for CV compared with TP in the second hour. Sweat rate (msw) was significantly higher for CV compared with TP (560 ± 45 g · h^-1 vs. 409 ± 84 g · h^-1, respectively). Subjective thermal comfort was not significantly different. Conclusions: TP was more effective than the CV in reducing heat strain under the conditions used in the study. Until a significant breakthrough in reducing heat strain while wearing NBC clothing in field conditions can be found, TP appears to be an effective and recommended cooling method.