## 1 Introduction
[15] numerically studied (Computational Fluid Dynamics--CFD modeling) the most effective way to assure the exhaust of smoke in the event of a train on fire, stopped beside the platform of a subway station provided with PSDs. Their conclusion was that the best ventilation strategy is ensured by activating the exhaust system from the tunnel ceiling and the exhaust system from the platform. Another ventilation approach was proposed by [PERSON] et al. [16] in the case of a train fire at subway station with PSDs, based on CFD simulations: the station air supply system, platform exhaust system, and the over track exhaust system are on, while the platform air supply system and under platform exhaust system are off. In addition, [PERSON] et al. [17] showed, also via CFD studies, that when using PSDs and ventilation systems, the time available for evacuation increased by almost 6 min compared to the scenario without PSDs (for the modeled subway station). [PERSON] and [PERSON] [18] performed CFD simulations for an island-type subway station, equipped with PSDs, in the event of a fire on the platform. They concluded that opening the PSDs on both sides of the platform improved the efficiency of mechanical smoke exhaust and therefore the time to maintain safe evacuation conditions for people increased. The effect of PSDs on smoke evacuation from a subway station was also studied by [PERSON] et al. [19], by performing twenty-four CFD simulations for different PSD switch modes. The results showed that the closing/opening of the PSDs is deeply related to the position of the fire and the ventilation systems available in the station. The impact of PSDs on the evacuation of smoke and pollutants was also studied by [PERSON] et al. [20] for a subway station with three underground levels, using CFD modeling. The results of the simulations performed for eight emergency situations indicated that the optimal smoke control (including opened/closed PSDs) depends on each fire scenario considered. Consequently, based on the studies mentioned above, it is not possible to generalize the solutions considered effective in terms of increasing the safety of passengers on subway networks, from one configuration to another. In order to implement adequate systems, as well as their correct use (e.g., coupling ventilation systems/PSDs) depending on the situation, it is necessary to carry out in-depth studies, specific to each analyzed configuration. In this context, as it is planned that the stations of the Bucharest subway network be retrofitted with PSDs, the purpose of this work is to numerically investigate (CFD modeling) the efficiency in case of fire of the existing emergency ventilation systems for a typical metro station in Bucharest, in conjunction with the implementation of the new PSDs. The configuration taken into consideration is based on a two-underground-level subway station equipped with PSDs. The entire description of this configuration, as well as the hypotheses of the emergency situation, are given below, followed by details concerning the CFD model development and the presentation of results in terms of air flow, temperature, and CO and CO\({}_{2}\) concentrations in the computational domain, focusing on regions of particular interest (e.g., near the PSDs, station platform).