## 5 Conclusions  
The merits of a specialized and a general-purpose code to simulate a fire in the commercial area of an underground intermodal transportation station are investigated using a simplified fire model, whose results have been previously compared with those of an EDC combustion model. The following conclusions can be drawn from the results presented above.  
1. The simplified fire model yielded results that, far enough away from the fire focus, are in excellent agreement with those obtained using an EDC combustion model, while requiring appreciably lower CPU times. It was also found that, for a given HRR, the results of the simplified fire model  
Figure 20: Same results as in Figure 5b, but obtained with FDS and FLUENT for Case G-4 (\(T_{\text{in}}\,=\,1500\) K).  
are fairly independent of the inlet velocity and temperature of the hot gases introduced at the fire focus.
2. The results obtained with FLUENT using the simplified fire model show a reasonable degree of agreement with those obtained with FDS, except regarding the mass flow rates of cold air entering through the natural vents and CO\({}_{2}\) mass flow rates through the west vent and forced ventilation grilles, for which some quantitative differences were observed.
3. The features that are most sensitive to using the different codes, fire models, computational grids and turbulence model settings are those describing the fire-induced oscillatory flow through the open vents, particularly the mass flow rate of cool air entering the domain. To the best of our knowledge, neither FDS nor FLUENT have previously been used to predict the type of fire-induced oscillatory flows through openings described in this paper, about which there is relatively little information in the literature.
4. The dependence of the oscillation frequency on the HRR was in reasonable agreement with the experimental and numerical results reported in the literature.
5. For the fire scenarios considered and versions of the codes used in this work, the main advantage of FDS over FLUENT was found to be its substantially lower CPU time consumption. On the other hand, FLUENT allows much more flexibility in grid generation for arbitrary geometries, and the simulation set up can be done more easily in FLUENT than in FDS.  
The results presented in this paper provide insight into the relative merits of specialized and general-purpose codes and different fire models, which are frequently used to assess fire safety levels in buildings in order to reduce risk to human life in the case of fire. The future work based on the presented results may be of help in devising fire safety solutions, aimed at limiting the zones of possible escape routes where people's survival could be compromised in the event of a fire.  
Conceptualization, C.Z., P.G., J.L. and J.H.; Investigation, C.Z., J.L.; Methodology, C.Z., P.G. and J.H.; Visualization, J.L.; Supervision, J.H.; Writing-original draft, C.Z. and J.H.  
This research was funded by Consorcio Regional de Transportes de Madrid, grant number OTRI-FUNED 5510003256.  
The support of the Consorcio Regional de Transportes de Madrid is gratefully acknowledged.  
The authors declare no conflict of interest.