## 1 Introduction  
Performance-based design (PBD) principles are commonly used to draw up fire protection plans [1]. In light of the multiplicity of ventilation and fire-fighting systems that may be operational, both theoretical and empirical studies are frequently made (see, e.g., [2]). The results of the corresponding tests will help in drawing up protection, extinction and evacuation plans, perhaps even suggest improvements in the infrastructures themselves [3, 4, 5]. As may be expected, the main inconvenience of this approach is the expense involved in full-scale experiments. Computational tools have contributed much to PBD in the case of confined areas such as stations, road tunnels, underground carparks shopping centres and stairwells of high-rise buildings [6, 7, 8, 9, 10]. Examples of reviews on field and zone approaches, turbulence, combustion, radiation, soot production and fire modeling in such scenarios can be found in [11, 12]. However, despite the advances made in computational sciences, numerically modeling fires in buildings is still far from being an easy task because of the multiple combinations of scenarios and materials involved, the resulting chemical reactions, turbulent transport of smoke and heat, etc. As a consequence, numerical models are invariably simplified, although even such simplification still requires vast computational resources because the wide ranges of scales involved and the multi-dimensional and unsteady nature of the problem cannot be avoided when analyzing complex real scenarios. To simulate compartment fires, the computational codes used include Fire Dynamics Simulator (FDS), FireFOAM, OpenFOAM, PHOENICS, FLUENT and CFX, among others (see, e.g., [7; 10; 12; 13; 14; 15; 16; 17]). All these codes have been extensively validated for a great variety of fire scenarios in the case of the first two and for a very large number of applications in the field of fluid mechanics in the case of the others. Despite the exhaustive validation of the codes, the uncertainties involved in experimental studies of complex large-scale fires (associated with data collection and the specification of the fire scenario and detailed experimental conditions), the variety of simplifications introduced in the governing equations for modeling turbulent transport and combustion processes, and the multiplicity of possible scenarios where a fire can occur, among other factors, introduce uncertainty in the assessment of the relative merits of different simulation tools, whether specialized or general-purpose. In this work we compare the performance and capabilities of a specialized code (FDS) [18; 19], which is a code specifically designed for low-speed fire-driven flows, developed by the National Institute of Standards and Technology (NIST), and a general-purpose code (FLUENT) [20] for the numerical simulation of a fire in the commercial area of an underground intermodal transportation station. Details on the verification and validation of FDS can be found, respectively, in Volumes 2 and 3 of the FDS Technical Reference Guide [21; 22]. Both codes, which are among the most frequently used in the literature to analyze, respectively, fire-related and general thermo-fluid dynamics problems, have been thoroughly validated against experimental results (see, e.g., [23; 24; 25]). However, the above mentioned uncertainties involved in large-scale tests, along with difficulties in obtaining well resolved solutions because of practical computer limitations and inappropriate specification of the numerical and boundary conditions settings, make it often difficult to assess the accuracy and efficiency of the codes used to simulate a fire in a particular complex facility. Furthermore, fires can involve a wide variety of scenarios, with different possible burning materials, which represents a huge challenge for simulation programs.