The effect of air permeability characteristics of protective garments on the induced physiological strain under exercise-heat stress

Objectives:The high values of thermal resistance (R_ct) and/or vapor resistance (R_et) of chemical protective clothing (CPC) induce a considerable thermal stress. The present study compared the physiological strain induced by CPCs and evaluates the relative importance of the fabrics' R_ct, R_et, and air permeability in determining heat strain.Methods:Twelve young (20-30 years) healthy, heat-acclimated male subjects were exposed fully encapsulated for 3h daily to an exercise-heat stress (35°C and 30% relative humidity, walking on a motor-driven treadmill at a pace of 5 km h¹ and a 4% inclination, in a work-rest cycle of 45min work and 15min rest). Two bipack CPCs (PC1 and PC2) were tested and the results were compared with those attained by two control suits - a standard cotton military BDU (CO1) and an impermeable material suit (CO2).Results:The physiological burden imposed by the two bilayer garments was within the boundaries set by the control conditions. Overall, PC2 induced a lower strain, which was closer to CO1, whereas PC1 was closer to CO2. Air permeability of the PC2 cloth was almost three times higher than that of PC1, enabling a better heat dissipation and consequently a lower physiological strain. Furthermore, air permeability characteristic of the fabrics, which is associated with its construction and weave, significantly correlated with the physiological strain, whereas the correlation with R_ct, R_et, and weight was poor.Conclusions:The results emphasize the importance of air permeability in reducing the physiological strain induced by CPCs.