## 4 Results and Discussion
### Flux from the Door
Conversely, the benefit of the slot cases is immediately apparent, with no case exceeding the gradient of the closed case and the 0.04 m\({}^{2}\) slot cases producing approximately the same effect as the 0.09 m\({}^{2}\) corner cases. From this analysis, it is suggested that slot cases were clearly more effective than corner cases at reducing heat transfer at the door of the compartment, given the location of the fire in this experiment. In general, it appears that the 0.16 m\({}^{2}\) opening cases are not the most effective in reducing the cumulative heat flux given the higher magnitudes than a selection of the 0.04 m\({}^{2}\) and 0.09 m\({}^{2}\) cases. However, the difference in criteria for identifying the flashover/steady-state phases for these experiments should be noted. In spite of this difference, they still exhibit much lower gradients, implying that, in practice, it is less likely that material CHFs will be exceeded, and in the case of exceedance, by a lesser margin. This will result in fewer and slower ignitions, and so it is recommended that larger opening areas are the most effective at reducing thermal exposure at the door. While useful, these cumulative flux plots do not give an accurate sense of another key factor for ignition--the variability in flux. For some of the experiments, it was discovered  
Figure 13: Cumulative heat flux curves in the post-flashover/steady-state phase, 30 cm from the door for (**a**) corner-open, (**b**) corner-poly, (**c**) slot-open, and (**d**) slot-poly horizontal opening cases. that the peak heat flux during the steady-state regime was significantly larger than the average. The trend was similar for both the open and the polycarbonate cases, shown in Figure 14. Here, for cases that had multiple experiments (e.g., three of C_Open_0.16), the peak and average values are taken across the steady states for all the relevant experiments. It is clear that the cases with small corner openings produced highly variable fluxes, with the 0.0025 m\({}^{2}\) polycarbonate case and 0.01 m\({}^{2}\) open case both spiking to values 231% of their respective steady state values. Generally, the slot opening cases produce much lower spikes relative to their averages. The variability appears to increase again as the area increases above 0.01 m\({}^{2}\); however, this should be set against the fact that the peak flux values for 0.16 m\({}^{2}\) cases are approximately 3-4 times smaller than the largest across the closed or small (0.0025-0.01 m\({}^{2}\)) cases. This may also partly be due to the semi-arbitrary method of defining the steady-state regime for the well-ventilated cases. Notably, reliable reductions in both peak and average fluxes relative to the closed case were achieved for all slot cases except the peak flux in the polycarbonate 0.01 m\({}^{2}\) case. However, flux reductions were not achieved for any corner cases below 0.09 m\({}^{2}\). The largest reductions in average flux for corner and slot cases were 65% (C_0.16 Open) and 69% (S_0.16 Open), respectively. From a database of materials found in an informal settlement [38], it is possible to identify some specific examples of materials which will be sensitive to highly variable flux in real fire scenarios (Table 3). Whilst these examples are highly specific and at values of flux not achieved in this experiment, they do show the importance of trying to limit the variability of heat flux from an opening. In real fire situations with large dwellings, spikes in flux of similar proportion to those achieved in the experimental small corner opening cases may be sufficient to reduce the time to ignition of a neighbouring dwelling by over 90%. Therefore, based on the conditions of this study, it is again shown that slot openings are more efficient at reducing risk relative to equivalent-area corner openings. Figure 14: Peak and average heat fluxes in the steady-state, 30 cm from the door for (**a**) corner and (**b**) slot opening cases, and (**c**) the ratio between peak and average flux in each case.