## 4 Questionnaire Results and Analysis  
### Comprehensive Subjective Evaluation  
Figure 13 presents the overall subjective evaluation voting values under the four different thermal stress levels. With the increase in heat exposure duration, the thermal sensation votes increased (Figure 13a). For the 21-23 \({}^{\circ}\)C working conditions, the overall average TSV values were distributed between 1 (slightly warm) and 2 (warm). Under the 23-27 \({}^{\circ}\)C conditions, the overall TSV values were between 1 (slightly warm) and 3 (hot). For the 27-29 \({}^{\circ}\)C conditions, the environmental thermal intensity obviously influenced the overall thermal sensation. The average thermal sensation voting value was 3.1, and the subjective thermal sensation was relatively hot.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **F** & **Significance** & \(t\) & \(p\)**(Sig.)** & **Mean Difference** \\ \hline \multirow{2}{*}{\(T_{sk}\)} & Equal variances assumed & 0.110 & 0.741 & \(-\)0.547 & 0.587 & 0.248 \\ \cline{2-7}  & Equal variances not assumed & & & \(-\)0.547 & 0.587 & 0.248 \\ \hline \multirow{2}{*}{\(HR\)} & Equal variances assumed & 2.758 & 0.106 & 0.870 & 0.391 & 2.464 \\ \cline{2-7}  & Equal variances not assumed & & & 0.906 & 0.371 & 2.464 \\ \hline \multirow{2}{*}{\(SW_{p}\)} & Equal variances assumed & 12.992 & 0.001 & 2.773 & 0.008 & 46.674 \\ \cline{2-7}  & Equal variances not assumed & & & 2.773 & 0.009 & 46.674 \\ \hline \multirow{2}{*}{\(M\)} & Equal variances assumed & 2.313 & 0.135 & 2.374 & 0.022 & 4.713 \\ \cline{2-7}  & Equal variances not assumed & & & 2.374 & 0.023 & 4.713 \\ \hline \hline \end{tabular} Note: \(p\)(Sig.) \(<\) 0.05 is significant.  
\end{table}
Table 6: Results of \(t\)-test analyses of the physiological parameters of male and female test participants.  
Figure 13: Comprehensive subjective evaluation voting (thermal sensation votes, humid sensation votes, thermal comfort votes, thermal acceptance votes) under four different working conditions (i.e., 21–23 \({}^{\circ}\)C, 23–25 \({}^{\circ}\)C, 25–27 \({}^{\circ}\)C and 27–29 \({}^{\circ}\)C). (**a**) TSV, (**b**) HSV, (**c**) TCV, (**d**) Thermal acceptability.  
At the beginning of the experiment, HSV was between 0 (neutral) and 3 (slightly wet) (Figure 13b). Within 30 min, the skin wetness sensation of the participants rose, and after 30 min, the skin wetness sensation tended to stabilize. In the thermal range 27-29 \({}^{\circ}\)C, HSV reached a very wet state. This suggests that at the beginning of the experiment, the body secreted sweat to increase the skin moisture. After half an hour, the stability of the feeling of skin humidity did not mean that the sweating had stopped. It was rather because the sweat had soaked the surgical gown and the outer protective clothing increased the resistance to sweat evaporation. The clothes stuck to the participants' skin and enhanced their wetness sensation.  
Figure 13c shows the change in TCV. The overall average TCV was between \(-0.5\) (neutral) and \(-2.5\) (very uncomfortable). As the thermal stress level increased, the participants' discomfort increased. Under the hot conditions of 27-29 \({}^{\circ}\)C, the TCV was between \(-1\) and \(-2.5\), and the discomfort was the most intense.  
Figure 13d shows the change in thermal acceptability. As the level of thermal stress increased, the thermal acceptability in each case gradually decreased, and the thermal acceptability was the lowest for the hot working conditions of 27-29 \({}^{\circ}\)C.