Auxiliary cooling: Comparison of air-cooled vs. water-cooled vests in hot-dry and hot-wet environments

Water-cooled, air-cooled, and ambient air-ventilated auxiliary cooling vests were evaluated in a hot-wet climate (HW) (35°C, 75% R.H.) and a hot-dry environment (HD) with additional infrared radiation (T(a) = 49°C, 20% R.H., 68°C black globe temperature). Twelve subjects dressed in full chemical warfare combat uniforms underwent 120 min of heat exposure in each combination of climate and cooling vest, except for the hot-dry environment and ambient-air vest. During each exposure, total exercise time was 20 min and rest time 100 min. This resulted in a mean time weighted metabolic rate of 180 W. Both water-cooled and air-cooled vests were sufficient for cooling in the HW climate heat storage (Δ S) was 13 and 7 W, final rectal temperature (T(re)) 37.4 and 37.3° C, and heart rate (HR) 124 and 112 b · min^-1, respectively. While using the ambient-air vest, all variables were significantly (p<0.05) higher ΔS, 25 W; T(re'), 37.7°C; HR, 139 b · min^-1; respectively). In the HD climate, both water and air-cooled vests were insufficient with a ΔS of 46 and 48 W, final T(re) of 38.4 and 38.3°C, and final HR of 151 and 147 b · min^-1. However, both cooling vests improved the subjects' physiological status compared to these predicted variables without auxiliary cooling. No significant differences were found between the air or the water-cooled vests in either the HD or HW climates. It was concluded that an air-cooled vest can be used with the same efficiency as a water-cooled vest. In contrast, the ambient-air vest was shown to have a low effectiveness in HW and to be dangerous in a HD climate.