Assessment of Advanced Personal Cooling Systems for Use With Chemical Protective Outer Garments

Persons responsible for removing extremely hazardous chemical agents or responding to chemical incidents typically wear fully encapsulating chemical protective ensembles (Level A (LA)) during field operations. LA ensembles are currently used without any ancillary cooling system, thereby greatly increasing the risk of thermal injury. The present study evaluated four candidate cooling systems intended to mitigate thermal stress experienced by LA ensemble users in hot humid conditions. Four current members (males, ages 22-24) of a military chemical response unit served as subjects in this study. Participants wore operationally configured LA ensembles with a closed circuit soda-lime based rebreather system while performing repeated rest (5 min)/work cycles (25 min: alternating treadmill walking (4.8 km/hr, 5% grade) and level walking while carrying 22.7 kg) designed to simulate tasks and workloads associated with actual missions for up to 2 hr. Air temperature was maintained at 37 deg C with relative humidity = 75% throughout exposures. Tested cooling systems were: (1) liquid cooled vest with hood (ice cooling source); (2) phase change vest; (3) wetted vest; and (4) liquid cooled whole body garment (super critical air cooling source). The noncooled LA configuration served as the experimental control. No significant differences were observed between control and cooling runs. Subjects were unable to complete more than two rest work cycles (mean +/- standard deviation = 47.9 +/- 8.5 min) while experiencing changes in rectal temperature = 1.4 +/- 4 deg C and maximum heart rates = 167 +/- 11 beats/min. Runs terminated either because of breathing difficulties, high heart rates, or subject exhaustion. None of the cooling systems proved effective in overcoming the severe heat stress imposed on subjects. Hot breathing gas coming off the rebreather was originally thought to be a major factor contributing to the thermal burden but this proved incorrect. --Original contains color plates: All DTIC reproductions will be in black and white.