## 3 Results and Discussion  
### Construction Stage  
The concentrations of gases detected in the Lowari Tunnel during the construction stage are shown in Table 1. Minimum, maximum, and average values of each monitored day are presented for all six gases. The H\({}_{2}\)S content changed slightly between 0 and 2.8 ppm, far below the threshold limit value. NO levels varied between 0 and 26.3 ppm, CO levels ranged between 0 and 450 ppm, while CO\({}_{2}\) levels ranged between 0 and 14,333 ppm. NO surpassed the low alarming threshold (22.5 ppm) on three days and the high alarming threshold (25 ppm) on one day during the reported period. CO levels exceeded the low alarming threshold of 35 ppm for 23 days and the high alarming threshold of 200 ppm for 8 days. CO\({}_{2}\) levels surpassed the low and high warning levels for 6 and 3 days, respectively. The maximum concentrations of H\({}_{2}\)S, NO, CO, and CO\({}_{2}\) (i.e., 2.8 ppm, 26.3 ppm, 450 ppm, and 14,333 ppm, respectively) were detected on 6 December 2008 at 16:48 for Chainage 4 + 549 when the ventilation system was turned down following an explosion due to generator fuel shortage. Finally, oxygen was found to be acceptable (>19.5% minimum) and its concentration did not vary considerably throughout the recorded duration. Figure 2 depicts the hourly concentration trends of gases in the Lowari Tunnel during blasting and making operations. Figure 2a demonstrates that 15 min after the explosion, the NO concentration reached a maximum of 26.3 ppm. During the subsequent 45 min (mucking activity), NO concentrations either declined gradually or stayed constant (\(\approx\)3 ppm). Figure 2b shows a significant increase in CO concentrations after the explosion, which peaked at 450 ppm in 12 min. The next 30 min (mucking activity) were marked by a considerable decrease in concentration, which was followed by 20 min of stable concentration. Figure 2c depicts a minor rise in the CO\({}_{2}\) concentration around 5 min after the explosion; nevertheless, the concentration observed during mucking activity on each subsequent day remained constant. A significant variation (about 30-fold) may be detected between the lowest and highest concentrations (450 ppm and 14,000 ppm, respectively). During the gas monitoring period of the construction stage of the Lowari Tunnel, NO, CO, and CO\({}_{2}\) levels exceeded permissible limits. The explosives used for blasting, as well as the loaders and dumpers used for mucking, caused excessive emissions. During the blasting action, NO exhibited the maximum increase, followed by CO and CO\({}_{2}\). According to the medical record register of the tunnel doctor, the high concentrations of these gases caused chest and throat diseases among the laborers. \begin{table}
\begin{tabular}{r r r r r r r r r r r r r r} \hline \hline \multirow{2}{*}{**Month**} & \multirow{2}{*}{**Date**} & \multicolumn{2}{c}{**H\({}_{2}\)S (ppm)**} & \multicolumn{2}{c}{**SO\({}_{2}\) (ppm)**} & \multicolumn{2}{c}{**NO (ppm)**} & \multicolumn{2}{c}{**CO (ppm)**} & \multicolumn{2}{c}{**CO\({}_{2}\) (ppm)**} & \multicolumn{2}{c}{**Oxy (\%)**} \\ \cline{3-14}  & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} & \multicolumn{1}{c}{**Range**} & \multicolumn{1}{c}{**Ave.**} \\ \hline  & 1 & Nover 2008 & 0.0 \(\pm\) 0.3 & 0.1 & 0.0 \(\pm\) 0.0 & 0.0 & 1.2 \(\pm\) 0.5 & 3.3 & - & - & - & - & - & - & - \\  & 3 & November 2008 & - & -