## 3 Results and Discussion  
### Effects of Fire Size  
During the simulations, several types of HRRs were considered, i.e., 0.5 MW, 1.0 MW, 1.5 MW, 2.5 MW, and 3.5 MW. Figure 4 was obtained from the FDS, in which there was a sharp increase in the velocity of smoke flow in accordance with an increase in the fire HRR. In addition, with an increase in the height, there was a decrease in the velocity of smoke flow from 2.5 m/s near the fire to 1.75 m/s away from the fire on the top floor. The buoyancy plume driving force decreased in accordance with an increase in the distance from the fire source. Moreover, an increase in the fire HRR would contribute to a more pronounced wall attachment effect on the side away from the fire. The air near the side wall (especially the left side) was identified to move at a higher speed, namely, most of the air flow was in the forward direction along the wall at a high speed. Buoyancy-driven thermal smoke has a significant influence on the temperature distribution in a stairwell [18]. Based on Figure 3, the influence of the fire HRR on the temperature distribution in the stairwell could not be clearly determined. Hence, the temperatures recorded using the thermocouples placed on each floor during the simulations were employed for further evaluation. Figure 5 presents the changes in temperature with respect to different fire HRRs (0.5 MW, 1.5 MW, 2.5 MW, and 3.5 MW), wherein curves of different colors represent different heights. It was concluded that an increase in the power of the fire source resulted in an increase in the temperature of the stairwell. At a fire HRR of 0.5 MW, the maximum temperature of Floor 1 was 80.3 \({}^{\circ}\)C, whereas at a fire HRR of 3.5 MW, the maximum temperature of Floor 1 was 241 \({}^{\circ}\)C, which is nearly greater than the value at a fire HRR of 0.5 MW by a factor of 3. Furthermore, the temperature curves of the lower floors were few and widely spaced; whereas for higher floors, the temperature curves were closely spaced. In particular, the temperature difference in the near-fire area was more pronounced, and the temperature difference in the area far away from the fire was smaller. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group** & **Test** & \ \begin{tabular}{c} **Fire HRR** \\ **(MW)** \\ \end{tabular}  & \begin{tabular}{c} **Atria Fire** \\ **Location** \\ \end{tabular}  & **Opening Locations** \\ \hline \multirow{8}{*}{**I. Varied fire size**} & 1 & 0.1 & 1 F & 1F, 21F \\ \cline{2-5}  & 2 & 0.25 & 1 F & 1F, 21F \\ \cline{2-5}  & 3 & 0.5 & 1 F & 1F, 21F \\ \cline{2-5}  & 4 & 1 & 1 F & 1F, 21F \\ \cline{2-5}  & 5 & 1.5 & 1 F & 1F, 21F \\ \cline{2-5}  & 6 & 2.5 & 1 F & 1F, 21F \\ \cline{2-5}  & 7 & 3.5 & 1 F & 1F,21F \\ \hline \multirow{8}{*}{II. Varied fire location} & 1 & 1.5 & 1 F & All open \\ \cline{2-5}  & 2 & 1.5 & 5 F & All open \\ \cline{2-5}  & 3 & 1.5 & 10 F & All open \\ \cline{2-5}  & 4 & 1.5 & 15 F & All open \\ \cline{2-5}  & 5 & 1.5 & 1 F & 1F, 21F \\ \cline{2-5}  & 6 & 1.5 & 5 F & 5F, 21F \\  
To further evaluate the temperature variation with respect to the fire HRR and increase in height, the maximum value of the temperature increase is presented in Figure 6, wherein curves of different colors represent different heights. Figure 6 shows that the slope of the red curve (Floor 1, 1.5 m) had the maximum slope, whereas the gray curve (Floor 21, 85.5 m) had the minimum slope. In particular, the maximum value of the temperature increase is presented in Figure 6.  
Figure 4: Velocity of smoke flow at different fire HRRs with only 1F and 21F open (all at 300 s). Figure 5: Temperature variation of different measuring points (at different floors) in the stairwell at different fire HRRs (0.5 MW, 1.5 MW, 2.5 MW, and 3.5 MW). with an increase in the height, the influence of the fire HRR decreased. This was due to the cold air caused by the air entrainment [3; 18], which resulted in a decrease in temperature due to the neutralization of hot and cold air.