# Applicability of Human Thermophysiological Model for Prediction of Thermal Strain in PPE
Moreover, the model was comprehensively validated [20; 21; 22] and also used for the prediction of heat stress by the Universal Thermal Climate Index (UTCI) [23], which was established as a more-complex and -advanced alternative to the wet bulb globe temperature (WBGT) [10]. The FIALA-based models are well designed for the evaluation of protective clothing, which can help to design safe periods of exposure and workload in these garments [21; 24]. Using thermophysiological models, it is possible to consider most of the objectively measured factors mentioned above to predict the transient changes of the deep body temperature and local surface temperatures. Currently, there are a number of thermophysiological models for thermal stress simulations, but most of them assume normal climatic conditions and reflect the thermal insulation properties of clothing (normal sports or work clothing) to a certain extent only, e.g., the predicted heat strain (PHS) model described in ISO 7933 [19] or the FIALA model of thermal comfort (FMTK), which includes the thermoregulatory response of the body [15; 20]. These models are intended to be used by occupational health specialists to evaluate working conditions. However, protective clothing against heat, cold, or contaminated environments is outside the framework of applicability of the standard methods such as PHS or the WBGT for these exceptional conditions with regard to the specific properties of any particular PPE needs to be further validated [10]. An example of an application designed to estimate the thermal behavior of the body when using protective clothing under extreme conditions is the Cold Weather Ensemble Decision Aid (CoWEDA), a computational tool developed by the U.S. Army Research Institute of Environmental Medicine (USA) to estimate cold stress for different variants of protective clothing under defined cold weather conditions [25]. The application is also based on the results of a thermophysiological model and measurements of PPE properties and is intended for planning equipment for military or civilian units. These recommendations help to ensure optimal protective clothing against cold and safe cold exposure time [25]. In our study, we developed a new user-friendly computational tool, the Predictor of Thermal Stress (PTS), for the prediction of thermal stress and the permissible duration of activity in PPE. The tool was based on pre-calculated scenarios that reflect a combination of experimental tests with human subjects wearing PPE in a climatic chamber. The PTS tool, as well as the climatic chamber tests covered four types of PPE--two types of impermeable chemical protective suits and an air-permeable firefighter suit and filtration (adsorptive) NBC suit. The local thermal insulation characteristics of all clothing were measured by using a 34-zone Newton thermal manikin. A total of 11,664 mathematical simulations were performed using the FMTK thermophysiological model with an \"average test subject\" based on test parameters' combinations. The results were used to create the core \"look-up table\" of the PTS tool, and the predictions were compared with the data obtained from the real tests subject. The PTS tool was validated using the results from the real tests with human probands in the climatic chamber.