Heat Strain Imposed by Toxic Agent Protective Systems

This study evaluated physiological heat strain from two developmental toxic agent protective systems compared to the standard Toxicological Agent Protective (TAP) suit during exercise-heat stress. Eight subjects (six men, two women) completed three experimental trials, at 38C, 30% rh, wearing: 1) Self Contained Toxic Environment Protective Outfit (STEPO) with rebreather (STEPO-R); 2) STEPO with tether (STEPO-T) or 3) the standard TAP. The STEPO systems provided effective body cooling of,; STEPO-R, 200 +/-36 W; and STEPO-T, 186 +/-59 W. TAP had no cooling. All experimental trials used treadmill walking at 0.89 m'sec-1, 0% grade at exercise/rest cycles of 20/10 min for 240 min. Metabolic rates for the treatments were: STEPO-R, 298 +/-26 W; STEPO-T, 299 +/-34 W; and TAP, 222 +/-40 W. Rate of heat storage was less (p<0.05) in STEPO-R (37 +/-8 W'm-2) and STEPO-T (38 +/-12 W'm-2) than in TAP (77 +/-15 W'm-2). Sweating rate was less (p<0.05) in STEPO-T (10.0 /- 4.8 g'min-1) than in TAP (23.8 +/-11.4 g'min-1). There was no difference between STEPO-R (12.3 +/-5.6 g'min-1) and the other two uniform systems. Subjects did not complete targeted exposure times of 240 minutes. Exposure time was longer (p<0.05) in STEPO-R (83 +/-22 min) and STEPO-T (106 +/-39 min) than in TAP (46 +/-10 min). Predicted time to 39.0C was less (p<O.O5) in TAP (69 +/-20 min) than in either STEPO-R (226 +/-124 min or STEPO-T (244 +/-170 min). The results of this study show that cooling in STEPO significantly reduced heat storage relative to TAP. The new generation toxic cleanup uniform systems effectively reduced heat stress and increased work capabilities compared to the standard TAP suit.