###### Abstract  
This paper presents a detailed analysis of the dynamics of indoor environmental parameters under three simulated fire scenarios in a multi-story building, using the PyroSim platform (based on the Fire Dynamics Simulator--FDS). The study compares two smoke control strategies, organized natural ventilation (a passive system) and mechanical pressurization (an active system), evaluating their influence on temperature, differential pressure, air velocity, heat release rate (HRR), and toxic gas distribution. The simulations revealed that passive systems, relying on the stack effect and vertical natural ventilation, do not ensure the effective control of smoke infiltration into evacuation routes, allowing significant heat accumulation and reduced visibility. The results highlight the superior effectiveness of unidirectional mechanical pressurization in maintaining a stable flow regime, functional visibility, and a safe evacuation environment. A key finding is the transition from static pressure control to velocity-based flow control at the moment of door opening toward the fire source. The results confirm that a dynamically adapted application of mechanical pressurization--synchronized with the opening of access pathways--not only reinforces existing principles for protecting egress routes, but also provides a precise operational approach for optimizing emergency responses in high-rise buildings. f 2025 28 May 2025 15 June 2025 18 June 2025 18 June 2025 19 June 2025  
cyanide (HCN), and other toxic gases that can accelerate the heat release rate (HRR). This highlights the necessity for achieving an optimal safety balance in ventilation design and the need for regulatory frameworks governing smoke toxicity [7; 8; 9]. CO and soot particle emissions in mechanically ventilated fires are influenced by the ventilation rate and the fuel container's size. Higher CO concentrations are observed under low ventilated conditions, while well-ventilated environments tend to produce more soot. This demonstrates the complex interaction between fuel characteristics and ventilation parameters in managing pollutant emissions during fires. The opening of upper natural vents accelerates the spread of smoke, and natural ventilation alone is insufficient to ensure occupant safety [10]. Although intuitive, natural ventilation fails to effectively prevent smoke infiltration into stairwells [11], amplifying the stack effect and justifying continued research into mechanical pressurization, which has shown greater efficiency [12; 13]. However, modern airtight buildings pose new risks related to positive pressure ventilation (PPV) and uncontrolled smoke migration during fires, underscoring the importance of strategically controlled ventilation to ensure both evacuation safety and structural integrity [14]. Positive pressure ventilation can either isolate smoke or unintentionally entrain it. Without optimized pressurization, the stack effect may transform airflow into a vector for contaminating egress routes [15]. Ventilation significantly influences fire dynamics in enclosed compartments, affecting combustion efficiency, temperature, and flame stability. Changes in ventilation may either enhance safety or increase the risk of re-ignition and unburnt gas accumulation [16; 17]. In airtight compartments, the rapid rise in the pressure differential (from 100 Pa to 1650 Pa within less than 50 s of ignition) can obstruct egress routes, reverse ventilation flows, and compromise structural stability. Therefore, technical solutions for controlled pressure relief and optimized ventilation are essential in fire safety design [18]. Current fire safety research typically examines natural ventilation and mechanical pressurization separately. Natural ventilation is sustainable but is compromised by the stack effect [10], while mechanical pressurization enhances evacuation safety but requires precise pressure control [19]. Our study uniquely integrates both methods under identical fire conditions.