## 5 Obtained Results by the Numerical Modeling
### Case A2 (Current Situation and Fire in the S. Pietro Ramp)  
With the assumed fire on a dumper at the S. Pietro ramp, which is between Levels D and E, the diffusion of toxic fumes develops mainly at Level D. There is a progressive expansion of the area with toxic gas concentrations that are higher than the maximum permissible values. After around 12 min from the start of the fire, the concentration of CO exceeds 25 ppm in the Prato Nuovo ramp also (between Levels D and E), which could be used by miners when fleeing active mining sites toward the surface.  
Case B1 (the Situation with the Advised Improvements to the Ventilation Circuit and Fire at Level F)  
With the three interventions that are advised for the improvement of the ventilation circuit (Section 4), a clear improvement in environmental conditions and in the supply of fresh air in the deeper active levels of the mine (Levels E and F) is achieved. However, with the triggering of a fire in Level F, one of the two access ramps to that level (ramp E-F) immediately reverses the flow of ventilation, thus allowing the fumes to rapidly invade Level E and the area of access around the Prato Nuovo ramp. After only 5 min from the ignition of the fire, dangerous levels of CO invade the access area to the San Pietro ramp, thereby preventing evacuation to the outside from that escape route (Figure 6a); after 7 min, the second access ramp to Level F also reaches CO concentrations that are incompatible with survival (Figure 6b). After 8 min, the Prato Nuovo ramp is saturated with the smoke that is produced by the fire. In practice, the advised improvements do not allow better evacuation conditions for miners during the emergency.  
Case B2 (Situation with the Planned Advised Improvements to the Ventilation Circuit and Fire in the S. Pietro Ramp)  
With the fire on the San Pietro ramp, the fumes produced tend to slowly invade Level E. However, this leaves the possibility of escape through the Prato Nuovo ramp. Only after approximately 12 min from the start of the fire do the toxic fumes (CO) reach the E-F additional ramp and, subsequently, part of Level F; the CO\({}_{2}\) concentrations become dangerous at Level F only after 20 min from the start of the fire. Escape is, however, still  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Case A1** & \\ \hline \hline  & **Monitoring points** & **Minutes after which air is unbreatable** \\ \hline \hline  & Level E & 12 \\ \hline \hline  & **Ramp E–F** & 13 \\ \hline \hline
**Case B1** & \\ \hline \hline  & **Monitoring points** & **Minutes after which air is unbreatable** \\ \hline \hline  & Level E & 5 \\ \hline \hline  & **Ramp E–F** & 8 \\ \hline \hline
**Case B2** & \\ \hline \hline  & **Monitoring points** & **Minutes after which air is unbreatable** \\ \hline \hline  & Level E & 20 \\ \hline \hline  & Ramp E–F & 30 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Minutes beyond which the air becomes unbreatable due to the fire fumes in two different critical points of the mine, which are at Level E and on the ramp E–F, which connects Levels E and F.  
always possible through the alternative ramp (ramp E-F) and the Prato Nuovo ramp, where the concentration of the CO never reaches the threshold value of 25 ppm.