# Fire Risk Analysis in Large Multi-Compartment Structures Using a Hybrid Multiscale Approach
## 3 Proof of Concept
### Application to a Multi-Story Office Building
#### 3.1.2 Network Model Results
The simulation covered the first \(21^{\prime}\) of fire, before the transmission of the fire to the adjacent rooms of compartment A08. Figure 13 shows the smoke concentration field after \(15^{\prime}\) of fire. Figure 12: First fire scenario in the four-story building: smoke maps predicted by the network model after \(6^{\prime}\), \(10^{\prime}\), \(15^{\prime}\), \(17^{\prime}\), \(21^{\prime}\), \(25^{\prime}\), \(32^{\prime}\), and \(36^{\prime}\) of fire. The areas in gray correspond to compartments where the smoke height is less than 1.80 m.  
The filling chronology of the building predicted by SAFIR is given in Figure 14. This chronology is relatively close to the one determined by the network model (Figure 12). The smoke first fills floor A, in less than 15\({}^{\prime}\), and then moves towards the stairwell (A06). The filling of the upper floors (B, C and D) starts with room D15 in 15\({}^{\prime}\) and then is simultaneous for rooms 09 of floors B to D (17\({}^{\prime}\)). Note that the filling of floor D earlier than that of floors B and C is due to gravity, as well as the size and configuration of the building. The hot smoke rises to floor D and accumulates there before filling floors B and C almost simultaneously. For a taller building, the smoke would have cooled more before reaching the top floor, likely promoting the filling of the intermediate floors. Before the ignition of rooms A04, A07, and A08, 18 rooms are filled with smoke up to 1.80 m above the floor. As assumed in the simple filling model, rooms fill up one after the other up to the height of the soffits, and then spread the smoke to adjacent compartments. When a room is connected to several rooms by a door (e.g., A08), the smoke is distributed evenly, and in the case of a connection through a horizontal opening (here, the stairwell), all connected upper rooms fill almost simultaneously. The histogram in Figure 15 compares the filling times obtained with the network model and SAFIR. The network model slightly underestimates the filling times, i.e., the  
Figure 14: First fire scenario in the four-story building: smoke maps predicted by the 3D CFD code SAFIR after 6\({}^{\prime}\), 10\({}^{\prime}\), 15\({}^{\prime}\), 17\({}^{\prime}\), and 21\({}^{\prime}\) of fire. The shaded areas correspond to compartments where the smoke height is less than 1.80 m.  
Figure 13: First fire scenario in the four-story building: smoke concentration field (in ppm) predicted by the 3D CFD code SAFIR after 15\({}^{\prime}\) of fire. rooms fill up faster. In the CFD simulation, the smoke tends to accumulate on the second floor, to the detriment of the upper floors. One of the reasons for these discrepancies is that the correlation of [PERSON] et al. [29], validated on corridor fires, is not fully adapted to the configuration of the building. With the network model, the smoke does not cool fast enough, which accelerates the successive filling of the rooms. However, the comparative analysis shows a satisfactory agreement, in terms of chronology and filling times, with an average deviation of approximately 3\({}^{\prime}\). Second fire scenarioWhen the emergency exits are open, the propagation of smoke is influenced by the ventilation. The smoke filling chronology obtained with the SAFIR code in this configuration is shown in Figure 16. It differs significantly from that obtained when the emergency exits are kept closed (Figure 13). The first rooms to be filled are the archive room A08 and the main entrance A04, after 6\({}^{\prime}\) of fire. After 15\({}^{\prime}\), the smoke fills the offices A14 and A15, it circulates to the upper floors and invades the co-working spaces C09 and D09. From 17\({}^{\prime}\) onwards, a difference in filling between the four floors of the building can be noticed. The smoke invades first the spaces on floors C and D (D08, C14, C15, D14, and D15), while the filling of floor B just starts (B09). The co-working spaces A07 and A09 are filled with smoke.