## 4 Discussion and Application Field of the Model  
The following observations can be made from the Figures 13-17:  
* The global profile versus time is well captured;
* The obtained steel temperatures are safe-sided for all levels. The peak temperatures are quite close to the ones measured during the test, except for mid-levels (3 and 4) where a non-negligible difference is found: for levels 1 and 2 the difference is around 90 \({}^{\circ}\)C (900 \({}^{\circ}\)C for the model versus 810 \({}^{\circ}\)C for the test). For levels 3 and 4 the difference is around (respectively) 150 and 190 \({}^{\circ}\)C (900 \({}^{\circ}\)C for the model versus, respectively, 750 and 710 \({}^{\circ}\)C for the test). For level 5, the peak temperature is similar, around 710 \({}^{\circ}\)C;
* The time during which the steel temperatures are high (i. e. above 500 \({}^{\circ}\)C--threshold arbitrarily chosen in a domain where the yield strength of steel has started to decrease) is slightly longer for the model than for test at levels 1, 2 and 3 (around 27 min for the test and 30 min for the model). However, for levels 4 and 5 a very good match is observed with 30 min for both the model and the test;
* However, for steel temperatures above 700 \({}^{\circ}\)C (temperature for which the yield strength of steel has significantly decreased) the difference is more important. With the model, steel temperatures are above 700 \({}^{\circ}\)C during 25 min for levels 1, 2, 3 and  
Figure 16: Steel temperature—Test n°2 versus analytical model and analytical model combined with zone model at level 4. Figure 17: Steel temperature—Test n°2 versus analytical model and analytical model combined with zone model at level 4. 4 and 15 min for level 5 while for the test this duration is approximately 10 min for levels 1 and 3, 12 min for level 2 and 5 min for levels 4 and 5;
* The developed model considers only the effect of the spreading localised fire, and needs to be coupled to a zone model for the upper levels to consider the hot gases which develop under the ceiling. For the highest level (level 5 which is located 40 cm below the ceiling), the application of the model only leads to unsafe results for the heating branch and to a good representation of the peak temperatures. The combination with a zone model allows to improve the representation of the fire; the peak temperatures are unchanged, but the heating branch is better captured with safe-sided results. For the level 4, which is located 90 cm below the ceiling, the application of the model only leads to slightly unsafe results for the heating branch and to significantly safe-sided results for the peak temperatures. The combination with a zone model leads to significantly safe-sided results for both the heating branch and the peak temperatures (which are unchanged);
* The descending branch is underestimated once steel temperatures goes below 400 \({}^{\circ}\)C. Such issue was also noticed through CFD numerical modelling ([PERSON] et al., 2021); this can be explained by the model's inability to properly capture heat release from glowing embers, as well as the heat accumulated within the compartment boundaries. The present methodology has some limitations, some of them being directly linked to simplifications which have to be made in the frame of an analytical procedure. Obvious limitations are linked to the main basic assumptions of the model: the enclosure is rectangular (therefore not allowing for complex geometries--or necessitating to simplify them), the fire path is one-dimensional and the fire load is uniformly distributed on the floor area (while in reality, if some part of the compartment floor is free of fire load, it will not be subjected to the same heat fluxes). Furthermore, the effects of the boundary conditions on the fire plume are disregarded. Therefore, the exact location of the openings is not considered, making impossible the consideration of local effects (for example deceleration followed by acceleration of the fire when reaching an isolated opening, as shown by [PERSON] et al.