## 2 Modeling and Parameter Adjustment
### Simulation Setup  
In the simulations conducted using PyroSim, an essential aspect for controlling airflow and maintaining overpressure in the stairwell is the integration of a supply fan to generate differential pressure. In this context, one supply fan with a specified flow rate of 2 m\({}^{3}\)/s was introduced on the upper level (scenario S1), and two supply fans with a flow rate of 1 m\({}^{3}\)/s each were introduced in scenario S2. These fans were configured to simulate an atmospheric profile with a power law exponent of 0.2, and a profile origin set at 3.0 m for the fan located on the ground floor and 30 m for the fan located on the top floor. These settings enable the efficient modeling of air movement within the simulation domain, with the pressure ramp duration configured at 3 s.  
A constant heat transfer coefficient of 50.0 W/(m\({}^{2}\cdot\)K) was defined to accurately model heat exchange. In addition, the thermal boundary conditions for the fan surfaces were set with a fixed temperature, and the surface emissivity was configured at 0.9. The surface temperature was controlled using the TMPA parameter, with a ramp up duration for temperature set at 1.0 s, allowing for a smooth thermal transition. The fan was configured to operate continuously, without any deactivation conditions triggered by the differential pressure exceeding certain thresholds. The use of this fan system is critical for ventilation control in fire scenarios, ensuring both smoke containment and the maintenance of a controlled indoor environment. The selection of environmental parameters--pressure, temperature, and heat release rate (HRR)--was based on their critical influence on fire development and smoke movement in high-rise compartments, as emphasized in recent CFD-based studies on fire dynamics and ventilation efficiency [42; 43; 44; 45]. HRR was calibrated using the standardized t-squared fire growth model, adapted to the fire load and geometry of the scenario. Pressure and temperature boundary conditions were derived from realistic building operating conditions and refined through iterative sensitivity analysis to ensure both model stability and physical fidelity. The simulation setup aligns with the PyroSim user manual and adheres to European fire safety standards EN 12101-6 and EN 12101-13. The arrangement of temperature measuring points was based on capturing critical fire and smoke behavior within the fire-affected zone and along evacuation routes, while also monitoring airflow patterns influenced by the stack effect and mechanical ventilation. This setup allows for a comprehensive assessment of thermal stratification, smoke propagation, differential pressure effects, occupant safety, and firefighting conditions. The coordinates of the five monitoring points are listed below:  
* Fire Compartment: P1--X = 3.25; Y = 2; Z = 1.7 (m)
* Interior Stairwell: P2--X = 7.5; Y = 5.75; Z = 1.7 (m)
* P3--X = 7.5; Y = 5.75; Z = 15.45 (m)
* P4--X = 7.5; Y = 5.75; Z = 26.45 (m)
* Ninth Floor: P5--X = 3.25; Y = 2; Z = 26.45 (m)In complex fire simulations, the analysis of key parameter distributions--such as air velocity, temperature, pressure, and visibility--is essential for understanding the behavior of environments affected by fire. The use of slice files at various building heights (Figure 4) allows for the examination of how these variables change during the development of a fire event. This approach provides valuable insights for assessing safety conditions and evaluating the effectiveness of evacuation strategies. To evaluate fire development and smoke propagation, five monitoring points were placed in key areas: within the fire compartment, on three levels inside the stairwell, and on the top floor. These locations were used to record temperature, air velocity, CO, and CO\({}_{2}\) concentrations. As shown in Figure 4 their distribution enables the detailed analysis of thermal stratification, gas movement, and exposure conditions.