The distribution of moisture in state-of-the-art firefighter protective clothing was analyzed on a sweating torso. After one hour of sweating, only 35 % of moisture evaporated from the layers, but after another hour of drying out, only about 10 % of the supplied moisture remained in the clothing. Over 75 % of this moisture accumulated in the innermost three layers of the clothing system consisting of five and six layers, respectively. The interaction of the moisture transport properties of the different layers proved to be very important for the distribution of moisture. In particular, the neighboring layer of the underwear turned out to be dominant for the moisture distribution. Depending on its hygroscopic properties, it could even act as a water barrier.

It is important to understand the process of evaporation and steam transfer through firefighter protective clothing in order to be able to prevent steam burns. As humidity sensors are too slow to measure fast changes of humidity inside the clothing layers, temperature changes were used to analyze the evaporation of moisture. Temperature measurements turned out to be useful to predict the evaporation speed within the clothing layers, as temperatures remain constant during the evaporation. The measurements showed that the temperatures within the clothing layers containing a wet layer never rose higher than the temperatures within dry clothing. As soon as all moisture had evaporated, temperature increase followed exactly the curves of the measurements of dry samples.

X-ray radiography was used to quantify evaporation and moisture transfer in a multilayer firefighter protective clothing system with defined wetted layers exposed to low thermal radiation. Evaporation was faster and took place at higher temperatures if the moisture was located in the outer layers of the clothing system. Moisture that evaporated in the outer layers of the clothing system was found to move inwards and condense in the inner layers and on the cap of the measurement cell. Results found in this study correlated well with the findings of our former study based on simple temperature distribution measurements to determine moisture transfer in protective clothing layers at low level thermal radiation.

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