## 4 Temperature and FED Index  
Increased air temperatures may make it difficult for the people to move. This increase affects the train evacuation process. The critical temperature in a confined space, such as a tunnel, is the temperature where a person's movement and actions are impaired, and it is defined as 60 \({}^{\circ}\)C [43]. Figure 15 shows that, for every scenario, the temperature at the walking platform, at a height of 2 m, did not exceed 24 \({}^{\circ}\)C. In these conditions, the evacuation can be carried out normally. The calculation of FED with Pathfinder used the equations described in the SFPE Handbook of Fire Protection Engineering, 5 th Edition [44]. Only the concentrations of the narcotic gases CO, CO\({}_{2}\), and O\({}_{2}\) were used to calculate the FED value. \[\rm{FED}\ =\ \rm{FED}_{CO}\cdot\rm{V}_{CO_{2}}+\rm{FED}_{O_{2}} \tag{16}\]  
Figure 12: Lengthwise U velocity at symmetry plane y = 5.5 m and z = 3.5 m for Scenario A at different time frames (t = +180 s, +270 s, +600 s, and +720 s). Figure 13: Lengthwise mean U velocity for Scenario A, upwind from the fire source. This calculation does not include the effect of hydrogen cyanide (HCN), and the effect of CO\({}_{2}\) is only due to hyperventilation. Carbon dioxide does not have toxic effects at concentrations of up to 5%, but it stimulates breathing, which increases the rate at which the other fire products are taken up. \[\text{FED}_{\text{CO}}=3.317\cdot 10^{-5}\cdot\text{CO}^{1.036}\cdot V\cdot t/D \tag{17}\]  
where CO is the concentration of carbon monoxide (ppm \(v/v\) 20 \({}^{\circ}\)C), \(V\) is the volume of air breathed each minute (L/min), with its value being 25 L/min for an activity level of light work (walking to escape), \(t\) is time in minutes, and \(D\) is the exposure dose (% COHb), with its value being 30% for an activity level of light work. Hyperventilation due to carbon dioxide can increase the rate at which fire products are taken up. The multiplication factor is given by the equation  
\[V_{\text{CO}_{2}}=exp(0.1903\cdot\%\text{CO}_{2}+2.0004)/7.1 \tag{18}\]  
where % CO\({}_{2}\) is the volume fraction of CO\({}_{2}\) (\(v/v\)). The fraction of an incapatiting dose of low O\({}_{2}\) hypoxia is calculated as:  
\[\text{FED}_{\text{O}_{2}}=\frac{t}{exp\left[8.13-0.54\cdot(20.9-\%\text{O}_{ 2})\right]} \tag{19}\]  
where \(t\) is time in minutes, and % O\({}_{2}\) is the oxygen volume fraction (\(v/v\)). The measurement location for FED quantity sampling is 90% of occupant height. For example, FED data for an occupant with height = 1.8 m would be sampled 1.62 m above the occupant's location. When the occupant is not inside an FDS mesh, the FED calculation is paused until the occupant enters another mesh [31]. FED values never reached the critical value of 1, where a person is considered incapatated, but some interesting results were extracted. The maximum values of FED are presented in Table 1 and compared in Figure 14. As shown, the longer the activation of the ventilation system was delayed, the more the uptake of combustion products and toxic gases increases. This is also shown in Table 2 and Figure 16, where the results for the mean fed values for each case are presented. It is important to be mentioned that, while maximum FED values for scenario A are about six times lower than the values for Scenario C, the mean FED values for Scenario A are an order of magnitude lower than Scenario C.  
Figure 14: Max FED index for the three different scenarios and evacuation times.