# Applicability of Human Thermophysiological Model for Prediction of Thermal Strain in PPE
## 3 Results
### Validation of PHS and FMTK Thermophysiological Models  
In the preliminary study [24], we compared the predictions of the body core temperature increase using two thermophysiological models, the PHS and FMTK, with the experimental data measured in a real test in the climatic chamber with one proband. The aim of the study was to investigate the applicability of the two thermophysiological models for usage even out of the validity range regarding the insulation properties of the protective clothing. The results generally showed that, for both models (PHS, FMTK), the difference between the simulated and experimental values expressed in the form of the mean absolute error (MAE) was lower than 0.5 \({}^{\circ}\)C for the air-permeable suit. Moreover, the FMTK model showed good predictability for impermeable suits also, with an MAE value of 0.69 \({}^{\circ}\)C for an ambient temperature of 30 \({}^{\circ}\)C and an MAE value of 0.19 \({}^{\circ}\)C for an ambient temperature of 40 \({}^{\circ}\)C. On the other hand, the PHS model showed very high MAE values, around 1.8 \({}^{\circ}\)C and 1.2 \({}^{\circ}\)C, respectively, for the prediction of the body core temperature for the impermeable suits at the two ambient temperatures tested [24]. In this follow-up study, a series of simulation calculations was performed for the selected ensembles (Tiger Plus as a representative of the air-permeable protective ensemble and Tychem-F as a representative of the impermeable protective ensemble) and for external conditions with ambient temperatures of 25 \({}^{\circ}\)C and 35 \({}^{\circ}\)C. The resulting values were then compared with the average values from real tests under the same conditions. Examples of the behavior of each prediction model are shown in Figure 5 for the air-permeable Tiger Plus and in Figure 6 for the impermeable Tychem F.  
For the air-permeable Tiger plus ensemble, the PHS index was able to predict the rectal temperature more accurately than the much more complex FMTK model (Figure 5) at both ambient temperatures tested. A slight inaccuracy could be observed at an ambient temperature of 35 \({}^{\circ}\)C, where both models slightly overestimated the value of the rectal temperature in comparison with the experiments. For the impermeable Tychem F ensemble, the PHS index predicted unrealistic values of the body core temperature increase, as demonstrated in Figure 6, compared to the experimental data and also compared to the FMTK model prediction. The PHS index predicted a much faster increase of the body core temperature \(T_{re}\) than the probands achieved in reality under the given conditions. After comparing both models, the PHS and FMTK, the prediction performed by the FMTK model showed much better agreement with the experimental data for both temperatures for the impermeable ensemble. The calculated MAEs values for each type of protective ensemble and for both ambient temperatures are shown in Figure 7. The value of the MAE for the air-permeable ensemble Tiger Plus was lower than 0.4 \({}^{\circ}\)C for both ambient temperatures. In addition, the PHS model showed an even lower value of MAE compared to the FMTK model results. On the other hand, the FMTK model showed a good predictability of rectal temperature for the impermeable ensemble Tychem F, where the MAE value for both temperatures was lower than 0.4 \({}^{\circ}\)C, whereas the PHS model for this type of garment showed an MAE value many times higher. The MAE value was approximately 1.6 \({}^{\circ}\)C at an ambient temperature of 25 \({}^{\circ}\)C and approximately 1.4 \({}^{\circ}\)C at an ambient temperature of 35 \({}^{\circ}\)C.  
Figure 5: Examples of the simulation calculations of the body core temperature (\(T_{re}\)) increase using the PHS and FMTK models compared to real tests with 12, respectively 11 probands, for the air-permeable ensemble Tiger Plus (at ambient temperatures of 25 \({}^{\circ}\)C and 35 \({}^{\circ}\)C).