## 2 Modeling and Parameter Adjustment  
### Geometrical Model and Ventilation Setup  
This research focused on a public civil office building with a height configuration of B + GF + 9F (basement, ground floor, and nine upper stories), analyzing a fire scenario originating in a compartment on the ground floor--a highly challenging situation in terms of both occupant evacuation and smoke management in the stairwell (Figure 1). The stairwell is not equipped with natural lighting, as opening windows in the stairwell significantly reduces pressurization efficiency [27]. To ensure differential pressure between the stairwell and adjacent spaces, a fan was installed on both the ground floor and the top floor. While previous studies often employ multiple air injection points into the stairwell to achieve the required pressurization, this research targets existing buildings, where implementing extensive ductwork is structurally infeasible. As such, three scenarios were defined:  
* Scenario S0 simulates natural ventilation, relying on vertical smoke movement through passive openings and thermal buoyancy. * Scenario S1 represents mechanical pressurization with a single air supply at the top of the stairwell to prevent smoke infiltration during evacuation. * Scenario S2 uses dual mechanical pressurization, with air supplied at both the top and bottom of the stairwell to optimize airflow and smoke control. Maintaining effective stairwell pressurization to prevent smoke ingress in high-rise buildings requires both careful system design--capable of compensating for pressure differentials across floor levels--and real-time dynamic adjustment of fire door dampers. This ensures a constant and adaptive protection regime during fire emergencies [28; 29]. The basis for our building model lies in its reflection of a common layout found in many multi-story buildings, characterized by a central stairwell and two open compartments. This configuration aligns with typical conditions where doors remain open, thereby obviating the need for additional compartmentalization. Such a design effectively captures the essential dynamics of smoke propagation and ventilation, while ensuring computational efficiency. By avoiding the complexity of detailed geometric modeling, which could significantly increase computational time, we maintain a practical balance between accuracy and efficiency. Supported by previous research [10], which has validated its ability to accurately replicate critical fire phenomena such as the stack effect and smoke movement, this model is both representative and reliable for evaluating various ventilation strategies. In order to achieve a simulation that closely approximates real fire conditions, a series of assumptions were established, based on the requirements of SR EN 12101-6 [30] and SR EN 12101-13 [31]:  
* Positive pressure was applied exclusively at the stairwell level, using either a single fan with a 1 m \(\times\) 1 m supply duct located on the upper level (scenario S1), or two fans, each with a 1 m \(\times\) 1 m duct positioned on the upper and lower levels, respectively (scenario S2). This configuration was adopted considering that direct access to the fire compartment is provided through the stairwell. * Within the fire compartment, the presence of an exterior opening (a window) [32] with dimensions of 1.40 m \(\times\) 1.00 m was assumed. This opening was treated as a smoke and pressure exhaust path to the exterior. * It was considered that the door to the fire-affected compartment opens after 120 s in scenario S1 and 60 s in scenario S2, as a result of occupant evacuation. During  
Figure 1: Horizontal section through the building: the ground floor (**a**) and the top floor (**b**). firefighting operations, this door remains open, while all other doors connected to the stairwell are assumed to be closed. * The differential pressure between the stairwell and adjacent rooms, as established by standards, is approximately Pa 50 \(\pm\) 10 Pa [30].