## 2 Description of Experiments
Finally, \(\,\hat{\text{m}}_{\text{a}}\) [kg/s] is the air flow rate into the compartment through an opening and is evaluated by Equation (2):  
\[\,\hat{\text{m}}_{\text{a}}=0.52\text{A}\sqrt{\text{h}} \tag{2}\]  
where A and h mean the area and height of the opening. The ventilation factor of the openings in Figure 2 based on equation (2) is 0.0092 kg/s, which is the same for all. However, according to previous studies [26; 27], the ventilation factor needed to derive GER may differ from the theoretical value depending on the opening shape. Because of this, correlations [21] that do not take into account the effect of opening shape may have uncertainty. Therefore, the effect of changes in the opening shape with a fixed ventilation factor on fire characteristics should be investigated. As shown in Figure 2, openings of various shapes designed to have a constant ventilation factor were used in the experiment. The opening shapes were designed to more easily implement a wide range of GER values, including the range where abnormal behavior occurs (\(\phi_{g}\approx\) 0.6\(\sim\)1.2). The opening width (door width, DW) was changed to 0.10 m, 0.15 m and 0.20 m based on DW05, and the height (h) was changed to keep the ventilation factor constant. The name of each opening was determined by its width. Figure 3 presents a schematic diagram of the lab-scale calorimeter (LSC) [28] based on the oxygen consumption method [29; 30] used to measure HRR and combustion efficiency. A square hood with a side length of 1.5 m captures combustion products and surrounding air and exhausts them through an exhaust duct (D = 0.20 m). Part of the flow passing through the exhaust duct is sampled through two porous tubes. After undergoing a pre-process to remove soot and moisture, the sampled gas is introduced into the gas analyzer \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \(\mathbf{O_{2}}\) & \(\mathbf{CO_{2}}\) & \(\mathbf{CO}\) & \(\mathbf{UHC}\) \\ \hline Range (\%) & 0–25 & 0–20 & 0–10 & 0–1 (10,000 ppm) \\ \hline Error (\%) & \(\pm\)0.4 & \(\pm\)0.5 & \(\pm\)0.06 & \(\pm\)0.0012 \\ \hline Measurement method & Electrochemical sensor & \multicolumn{3}{c}{Non-Dispersive Infrared (NDIR)} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specification of a portable analyzer for measuring the concentration of chemical species. Figure 1: Schematic diagram of the 1/4 reduced-scale ISO 9705 compartment and installation location of measurement devices. (OXYMAT 61, ULTRAMAT 23). In addition to these measurements, the HRR is calculated through the additional consideration of the mass flow rate and the average cross-sectional temperature in the exhaust duct. Table 2 provides a summary of the experimental conditions considered in this study and the fuel flow rate to implement each GER. At room temperature (25 \({}^{\circ}\)C), the ideal HRR considering fuel density (1.808 kg/m\({}^{3}\)) and heat of combustion (46,400 kJ/kg) [31] ranges from 5.5 to 55.2 kW. Experiments for each GER were carried out for 600 to 1200 s, in which the measured HRR, temperature, incident heat flux, and species concentration reached a steady state and were sufficiently maintained. Changes in fire phenomena according to GER and opening shape were analyzed by comparing the averages at 100 s in the steady state, and the standard deviations in the form of vertical error bars were also presented. Figure 3: Lab-scale calorimeter based on the oxygen consumption method for measuring the heat release rate. Figure 2: Schematic diagram of openings designed to have a constant ventilation factor (0.52A\(\sqrt{\hbar}\)).