Physiologic Response to Transient Heat Stress in Reflective versus Non-reflective Clothing.

Six subjects wearing either nonreflective or reflective outer garments of equal insulative value (I clo) and unventilated were exposed in 96 experiments to heat pulses of 930, 1210, 1490, and 1770 C for 15, 12, 9, and 2 minutes, respectively. The experiments were designed to simulate a range of re-entry heat exposures produced by malfunction or failure of the air-conditioning system of the vehicle.' Total experimental time included the heat pulse and subsequent recovery period and was constant (40 minutes) for all conditions. Mean weighted skin and rectal temperatures, heart rate, total sweat produced and evaporated, and cardiacoutput, indirectly derived from blood pressure measurements, were the observed physiologic parameters. Evaluation of each parameter, individually, indicates that for some there is no relation between the physiologic response, the type of garment protection, and the level of thermal stress, while for others there is marginal benefit derived from wearing aluminized outer clothing. At only one timeintensity profile did the physiologic penalty of wearing nonreflective outer clothing appear more than marginal. However, even under the most severe conditions of thermal stress and absence of reflective protection, none of the physiologic responses approached tolerance limits in our terms of reference. The thermal protective effectiveness and practicality of the aluminized outer garment for intravehicular aerospace flights is also discussed.