###### Abstract
Using advanced CFD simulations and a validated model, we analyze key safety parameters. This novel approach connects fire dynamics with ventilation performance, improving evacuation and firefighting strategies. In Romania, a building is classified as high-rise if the highest usable floor exceeds 28 m, with those up to 45 m still considered high-rise, while structures above that height are classified as very tall buildings [20]. A review of international definitions shows variation: in the USA, a high-rise is defined as exceeding 23 m, measured from the fire department access point to the highest occupied floor [21]; in China, high-rise buildings are defined by fire safety regulations as residential buildings taller than 27 m, and multi-story factory, storage, or civil buildings taller than 24 m, according to the Code for Fire Protection Design of Buildings [22]; in the UK [23], buildings exceeding 18 m or having more than seven stories are considered high-rise. In the scientific literature, buildings over 35-36 m or 12 stories are often classified as tall [24], though this definition varies significantly depending on regulations and factors such as structural safety, wind loads, and urban integration, necessitating a flexible, context-sensitive classification approach. The importance of studying high-rise buildings arises from devastating fire incidents that have affected such structures, causing a significant loss of life and material damage. By implementing efficient evacuation strategies [25] and CFD-based numerical modeling [26], fire safety design in high-rise buildings can be improved. The present study focuses on optimizing mechanical pressurization systems for smoke confinement in stairwells, comparing them to organized natural ventilation. It evaluatesthe effectiveness of different smoke pressurization strategies based on the configuration of an B + GF + 9F (basement + ground floor + nine floors) office building and the dynamic conditions of fire scenarios simulated in FDS. Within this context, two essential mechanisms influence smoke dynamics in a compartment fire in a high-rise building: the stack effect and positive pressure mechanical ventilation (PPV). This research investigates the comparison between the stack effect and PPV for smoke control in an office building fire, addressing the following questions:  
* What is the importance of pressurization and controlled ventilation in fire management? * How do interior environmental parameters such as temperature, visibility, differential pressure, airflow velocity, HRR, and CO/CO\({}_{2}\) concentrations differ in a multi-story building fire scenario when using the stack effect versus positive pressure ventilation? * How effective are natural and mechanical ventilation systems in the analyzed scenarios at limiting the spread of smoke and toxic gases in an office building fire? This paper addresses the gap in studying natural and mechanical ventilation together in high-rise fires. Current studies typically evaluate them separately [10; 11; 12; 13]. We use advanced simulations to compare both methods under realistic conditions. This provides a clearer understanding of their combined effects on fire safety. The following sections present the structure of the numerical model used to simulate the above-mentioned phenomena, including geometric configuration, ventilation setup, simulation domain and mesh discretization, boundary conditions, fire source parameters, result discussions, and study conclusions.