## 7 Conclusions  
Ten quarter-scale (thermally thin bounded) ISO-9705 compartment fire experiments were conducted to investigate the effect adding horizontal openings in addition to the vertical openings on the fire dynamics, external radiation, and the ability of the LES  
Figure 22: Average compartment inlet fresh air during steady state period as a function of the updated ventilation factor. CFD model, namely FDS, to reproduce compartment fire dynamics with these boundary conditions. Nine of these experiments were then repeated where the horizontal openings were covered with a flammable plastic-based thin material (e.g., polycarbonate) to mimic the situation in informal settlements and understand the practicality of adding these openings to restrain the fire spread in informal settlements. The experimental results were also used to develop an empirical correlation for an updated ventilation factor and develop a coupling relation between the updated ventilation factor and the mass inlet air to the compartment. The conclusions of the study are as follows:  
* The efficacy of adding horizontal openings to reduce the heat flux to the surrounding and thus the potential fire spread risk was proven for horizontal openings located as a central slot compared to equivalent-area openings at the corners. The slot cases, relative to the corner cases, showed the ability to reduce heat fluxes from the door consistently at areas as low as 0.01 m\({}^{2}\)--and all cases above this--compared to the corner cases which only achieved reductions at a minimum of 0.09 m\({}^{2}\). The maximum reductions in average heat flux were 65% and 69% by the largest corner and slot cases, respectively. * Regarding the wider surroundings (at the back and side wall), slot cases of \(\geq\)0.09 m\({}^{2}\) caused reductions in both the average and peak fluxes relative to the closed case (up to 51% and 39%, respectively). However, corner cases only achieved reductions at 0.16 m\({}^{2}\) and by smaller margins (up to 36% and 13% for average and peak, respectively) with some cases of this size still actually exhibiting increases in peak flux up to 75%. * A new empirical ventilation factor was proposed to describe the flow field through both openings and was then coupled to the mass of inlet air with high accuracy. * The numerical simulations generally reproduced the main fire dynamics and trends within these under-ventilated compartments successfully. * The high turbulence and mixing at some cases were challenging to capture with a 5 cm LES filter. This highly affected the simulated combustion efficiency and gas temperature at some locations within the compartment. * The data produced were insufficient to establish any clear correlations relating to the differences between polycarbonate and open cases. No clear trends were observed in the time to flashover across different types and size of opening, despite an expectation that the presence of the polycarbonate sheeting may influence this. There was good agreement between polycarbonate and open cases for the average heat fluxes to surroundings and fair agreement between the peak fluxes. Future research should be focused on testing and understanding the limitations of the proposed empirical correlation; this study offers validation for the FDS code in these conditions to be used in future studies to enhance the empirical correlation and understand its limitations using numerical models rather than experimental work, in addition to understanding the effect of scaling these conditions on the end result. M.B. : conceptualization, data curation, formal analysis, investigation, methodology, validation, writing--original draft. K.O. : data curation, formal analysis, investigation, validation. F.R.C. : formal analysis, investigation, methodology, writing--review and editing. S.S.: formal analysis, writing--review and editing. L.G. : methodology, writing--review and editing. D.R. : methodology, funding acquisition, supervision, writing--review and editing.