# Applicability of Human Thermophysiological Model for Prediction of Thermal Strain in PPE
## 3 Results
### Validation of the PTS Tool Using Real Tests in Climatic Chamber  
Based on the results of the real tests in the climatic chamber and the statistical processing of the data, validation data for the PTS were prepared. The main aim of the validation was to compare the predictions of permissible work time with the real mean values of the maximum time achieved by several probands in the laboratory test in the climatic chamber under the given conditions (ambient temperature 25 \({}^{\circ}\)C and 35 \({}^{\circ}\)C, relative humidity 20-30%, corresponding to the real tests, given protective suits). It is important to remember that the tests could be terminated at \(T_{re}\) temperatures lower than 38.5 \({}^{\circ}\)C, either due to achieving the test limit of 125 min, reaching \(HR_{lim}\), or upon subjective request due to nausea, headache, unbearable discomfort etc. For this reason, the average value of the experimentally measured body core temperature at the end of the test was determined to be approximately 38.2 \({}^{\circ}\)C for the cases mentioned (25 \({}^{\circ}\)C and 35 \({}^{\circ}\)C). This value was then used to verify the look-up table. The values of the maximum achieved time in the tests (average value and standard deviation) are summarized in Table 5 and in the chart in Figure 11 (green columns). For the PTS tool's verification purposes, the average value of the input data (each proband's weight, height, age) was used to recalculate the tabulated metabolic activity or calculated metabolic activity for each real test and entered into the PTS tool. Work Regime 6 was selected (intermittent activity-20 min work + 10 min rest, 180 min in total), which most corresponds to the laboratory tests. The ambient temperature of 25 \({}^{\circ}\)C or 35 \({}^{\circ}\)C and the selected protective ensembles were gradually entered. The PTS was set to interpolation mode. Since the model indicates reaching the 38 \({}^{\circ}\)C, 38.5 \({}^{\circ}\)C, and 39 \({}^{\circ}\)C limits, a linear interpolation between these limits allowed the PTS to determine the time limit for reaching the body core temperature, \(T_{re}\), achieved in the corresponding set of tests on average. The results of interpolation are shown in the chart in Figure 11 (blue columns). The comparison of the real experiments with the PTS prediction showed a relatively good match; see Figure 11. It can be seen that the time limits pr  
Figure 11: Comparison of the results of the real tests (maximum time (min) achieved in the tests, average from all the tests performed under the same conditions with up to 12 probands as described in Table 5—green column with black error lines), and the PTS prediction values (time (min) when an “average” person reaches the “average” maximum body core temperature \(T_{re}\) measured in the corresponding set of real tests—blue column). suits were in agreement with the experimental results (the values of the predicted limiting time lie within an error bar representing the standard deviation of the experimental data). The prediction accuracy given by the PTS tool can also be expressed by calculating an MAE of 10.1 min or a MAPE of 12.6%. A similar comparison for the Tiger Plus with SCBA ensemble was performed. However, during the real tests, as many as 30-50% of the tests were terminated because of air exhaustion from both cylinders of the SCBA and not due to reaching the \(T_{re}\), \(HR_{lim}\), or because of the proband's request (see Table 5), and also, the PTS predictions did not show a good agreement with the real data. The PTS tool overestimated the predicted time limit for an ambient temperature of 25 \({}^{\circ}\)C and underestimated the predicted time limit for 35 \({}^{\circ}\)C. In addition, the predicted values of the permissible work time did not lie within the range of standard deviations of the experimental data measured. For this reason, the validation of this type of protective ensemble is not covered in the summary in Figure 11 and must be validated in the future with differently arranged real tests.