## 4 Results  
In the early period, the oxygen in the enclosure was enough to maintain burning, the burning was fuel-controlled, and the curves obtained were almost the same as the literature data. In cases 1, 2, 3, and 4, the fire was controlled by the ventilation, \(\varphi>1\), and the HRR did not follow standard test predictions (Figure 7a). The characteristics of the fire, compartment volume, and geometry did not enhance the burning rate, the HRR max value was below the standard data predictions, and the fire was prolonged. Figure 5: Enclosure model with partition wall and thermocouple trees. Figure 6: t-square growth, peak, and decay for fuel-controlled model fire. It is notable that there was a large amount of fluctuation in the HRR under all the ventilated conditions [18]. In cases 5, 6, 7, and 8, at the time after 200 s when the fire was fuel-controlled, \(\varphi<1\), and the HRR followed the standard test predictions (Figure 7b). We assumed that the cause of the fluctuations in the HRR was oxygen deficiency flow, and the temperature in the lower layer below the smoke was fairly homogeneous. The gas temperature of the lower layer was above the temperature of the incoming air in the enclosure due to mixing as the air entered the vent and descended into the enclosure. This mixing effect could be inferred from the air entering above the height of the smoke layer in the compartment, as it had to entrain some smoke as it plunged to the floor. It formed a lower layer flow that sought out the fire. This mixing effect was responsible for less oxygen being brought to the fire and it competed with an increasing temperature to control the fire. The described effect increased as the ventilation factor decreased. Under a ventilated enclosure, the fire would be sustained and reach the HRR according to the literature data. This indicates a difference between most of the data for burning materials in real fire conditions and standard test methods for measuring the HRR [19]. The fire characteristics under ventilated conditions did not cause a flashover/backdraft in cases 1, 2, 3, and 4. Under ventilated conditions, the fire could be sustained or self-extinguished. Figure 7: (**a**) Ventilation-controlled fire after growth phase \(\varphi>1\). (**b**) Fuel-controlled fire after 200 s; \(\varphi<1\) after 200 s.  
In cases 5, 6, and 8, a sudden increase in the ventilation factor did not cause flashover/backdraft [20]. Case 7 had the same ventilation characteristics as case 8 with a different geometry (Table 3). FDS accurately predicted the increase in the ventilation factor, ventilation height, and ventilation delay due to an abrupt change in the ventilation at 400 s; this followed the occurrence of flashover/backdraft in case 7 at 411 s. The enclosure temperature was represented with a mean value for the front at the door with \"temp. mean front\", at the middle of the model with \"temp. mean middle\", and near the fire location with \"temp. mean rear\" (Figure 8). The geometry in case 7 was an open space similar to the \"furnace\" testing methods, which enhanced the homogeneous temperature distribution in the enclosure under ventilated conditions of a sustained fire and accumulated unburnt gases. After an abrupt change in the ventilation factor, those gases ignited and caused a flashover/backdraft at 411 s.  
The side view of case 7 in Figure 9 shows that the flashover/backdraft started on the opposite side of the fire location, at the door, which increased the ventilation factor. Figure 8: (a) Case 7 without partition wall or flashover/backdraft at 411 s; (b) case 8 with partition wall and no flashover/backdraft. In case 8, the partition wall increased the heterogeneity of the enclosure temperature and reduced temperature and the possibility of a flashover/backdraft (Figures 8b and 9). In cases with a partition wall, the temperature was lower, and the heterogeneity increased (Figure 10).