## 4 Conclusions  
This paper contributed to better validation of the FDS 6 model of the Polana tunnel (Slovakia), which was originally developed and validated in [18] using the data from a full-scale tunnel ventilation test. The test included three modes of the ventilation operation during which airflow velocity was measured by the grid of five anemometers (with a measurement accuracy of 0.3 m/s) located at the distance of 300 m from the left tunnel portal and by three tunnel anemometers (with a measurement accuracy of 0.1 m/s). The former validation of the model indicated the very good accuracy of the time-averaged velocity of the steady-state tunnel airflow, but relatively poor accuracy of the velocity measured by tunnel anemometers. The improved representation of the tunnel anemometers and evaluation procedure (using the same length of time intervals with stabilized airflow and the same frequency of evaluated values in simulation and experimental data) led to the substantial improvement of the accuracy of airflow velocity measured by the tunnel anemometers. To evaluate the model's ability to determine the steady-state airflow velocity generated by emergency ventilation, the average airflow velocity calculated as the arithmetic mean of the measured velocities and the time-averaged airflow velocity calculated as the time-averaged velocity measured at selected time intervals were evaluated. Based on the simulation results analysis, the following conclusions can be specified: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**RD** & **Mode 1** & **Mode 2** & **Mode 3** \\ \hline Sim\({}_{\text{AT}}\) & 0.0416 (\textless{}5\%) & 0.0014 (\textless{}1\%) & 0.0212 (\textless{}3\%) \\ [18] & 0.1261 (\textless{}13\%) & 0.1647 (\textless{}17\%) & 0.1312 (\textless{}14\%) \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Relative difference RD [\(\%\)] between the experimental and simulated time-averaged airflow velocities determined by the tunnel anemometers. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{v_{avg}}\) & **Mode 1** & **Mode 2** & **Mode 3** \\ \hline Sim\({}_{\text{AT}}\) & \(-5.37\) m/s & 3.24 m/s & 5.25 m/s \\ ExpAT & \(-5.16\) m/s & 3.23 m/s & 5.14 m/s \\ [18] & \(-4.51\) m/s & 2.70 m/s & 4.47 m/s \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Time-averaged airflow velocity \(\mathbf{v_{avg}}\) [m/s] determined by the tunnel anemometers in the experiment and in both simulations considered. * Based on the use of an improved and extended validation procedure, both models (the one with improved representation of the tunnel anemometers and the previous one) provide very good simulation accuracy for the average and time-averaged airflow velocities measured by the grid anemometers. The simulation results were in good agreement with experimental data, with inaccuracies comparable to the measurement accuracy of the grid anemometers. The observed simulation accuracy can be considered being sufficient for practical applications of the model. * For steady-state airflow generated by emergency ventilation, the improved model provides relatively good accuracy of the average airflow velocity measured by the tunnel anemometers. The simulation accuracy was somewhat lower (below 0.5 m/s for the Mode 1, below 0.2 m/s for Mode 2 and below 0.4 m/s for Mode 3), but still relatively comparable to the measurement accuracy of the tunnel anemometers (0.1 m/s). However, if we take into account a 5-point moving average to calculate the velocities to illustrate the practical calculation of the velocity values by the tunnel control system, it turns out that the inaccuracies of the simulation results tend to decrease significantly. Such the simulation accuracy can be still considered sufficient for practical model applications. * After modifying the procedure for evaluating the simulation results, the improved model achieves much better modeling accuracy of the time-averaged airflow velocity measured by the tunnel anemometers, as reported in [18].