# The Impact of an Office Fire Combined with the Stack Effect in a Multi-Story Building
## 2 Modeling and Parameter Adjustment
### Burner Characteristics  
The fire source consists of nine ignition points arranged in stacks of wooden bars, as these more realistically replicate the destructive effects of a fire [39; 40; 41] (Figure 6a). The area of the burner is equivalent to the cumulative area of the nine stacks, resulting in a total burner area of 80.325 m\({}^{2}\). The thermal load established for the simulation corresponds to that of an office fire [42]. Figure 5: Monitoring sections. Figure 6: Wood stack configuration (**a**) and HRR evolution curve (**b**) [43]. Flashover is a critical phenomenon in fire dynamics, characterized by the fast transition from localized burning to widespread involvement of all combustible materials within an enclosure. This occurs when the HRR increases significantly, leading to a rapid growth of temperature and resulting in the simultaneous ignition of all exposed surfaces. Consequently, the environment reaches a point of generalized combustion, dramatically altering fire behavior and posing severe challenges to fire suppression efforts. In addition to the fire compartment area, A = 16 m\({}^{2}\), which corresponds to the average surface area of an office, the fire load density (FLD) value was established at 420 MJ/m\({}^{2}\), in accordance with current standards [42], resulting in a total heat release (HR) of 6720 MJ, obtained by multiplying the two. Given the knowledge of the HR value and the calorific value, H = 17.5 MJ/kg, the total mass of combustible material required for simulating such a fire, M = 384 kg, can be determined by dividing the two. The maximum value of the Heat Release Rate (HRR, kW) was determined using a specialized computational program [39] after inputting several simulation parameters, such as the stack configuration (Figure 6a), calorific power, ventilation condition, and total mass of the combustible material. This resulted in two output data points: the maximum HRR value, HRRMAX = 4350 kW, and its duration, t\({}_{\text{peak}}\) = 960 s.  
To obtain the HRR curve, another software program was used, designed to generate and simplify the HRR curve following the \(l^{2}\) method [43], based on previous studies [40; 44]. The evolution of HRR as a function of the square of time (\(l^{2}\)) is utilized to model fires because it more accurately reflects the manner in which they develop during the active burning phase [45], having the following dependency:  
\[HRR(t)=\alpha_{g}\cdot t^{2} \tag{2}\]  
where  
* \(HRR(t)\) is the Heat Release Rate at time \(t\),
* \(\alpha_{g}\) is the specific growth rate,
* \(t\) is the time elapsed since the onset of the fire. Within the specialized program [43] (Figure 6b), the following input data were set:  
* Initial delay = 10 s.
* Growth rate of HRR during the development phase, \(\alpha_{g}\) = 0.1876 kW/s\({}^{2}\). * Duration of the fully developed phase = 960 s (t = 160 to 1120 s). * Maximum HRR value = 4350 kW. * Decay rate of HRR during the regression phase, \(\alpha_{g}\) = 0.00293 kW/s\({}^{2}\). Having defined all the characteristics of the source, the next step involved obtaining the output data, such as the simplified evolution of the HRR and the value of the Heat Release Rate per Unit Area (HRRPUA) to ensure that the simulated fire corresponds to an office fire scenario. These two output data points were exported from the specialized software into PyroSim, with the HRRPUA set at 100 kW/m\({}^{2}\), a characteristic value for wood used in other studies [31]. Visibility within the building (meters) as a fire safety parameter for occupants plays a vital role in rapid and safe evacuation. This parameter is directly influenced by the amount of smoke generated during combustion, smoke that can quickly diminish the ability of individuals to orient themselves and evacuate the building. The soot yield, which is a measure of the amount of soot produced per unit mass of fuel burned, has been set by default to the value of 19.8%.