Chemical-biological protective clothing: effects of design and initial state on physiological strain

Purpose: This study examined whether heat strain during low states of chemical and biological protection (CBlow) impacted tolerance time (TT) after transition to a high state of protection (CBhigh) and whether vents in the uniform reduced heat strain during CBI,,, and increased TT. Methods: There were eight men who walked at 35 degrees C in CBlow and then transitioned to CBhigh. Subjects wore fatigues in CBlow with an overgarment during CBhigh (F+OG) or a new 1-piece (1PC) or 2PC uniform throughout CBlow and CBhigh. One condition also tested opened vents in the torso, arms, and legs of the 2PC uniform (2PC(vent)) during CBlow; these vents were closed during CBhigh. Also worn were fragmentation and tactical vests and helmet. Results: Heart rates were reduced significantly during CBlow for F+OG and 2PC(vent) (114 +/- 13) vs. 1PC and 2PC (122 +/- 18). Rectal temperature (T-re) increased least in CBlow for F+OG (0.86 +/- 0.23 degrees C) and was significantly lower for 2PC(vent) (1.02 +/- 0.25 degrees C) vs. 2PC (1.11 +/- 0.27 degrees C). T-re increased rapidly during CBhigh for F+OG, which had the shortest TT (40 +/- 9 min). Increased thermal stain during CBlow for 1PC negated its advantage in CBhigh and TT (46 +/- 21 min) was Similar to F+OG. Differences in T-re between 2PC and 2PC(vent) remained during CBhigh where TT was increased during 2PC(vent) (74+/-17 min) vs. 2PC (62 +/- 19 min). Conclusions: it was concluded that heat strain during CBlow impacted TT during CBhigh, and use of vents reduced heat strain during CBlow, thereby increasing TT.