# Behavior Characteristics of Hazardous Gas and Scattering Coal Dust in Coal Storage Sheds
## 5 Results and Discussion
### Concentration of Carbon Monoxide  
The boundary conditions for carbon monoxide concentration analysis appear in Table 4. Case 2-1 assumes the conditions in which spontaneous ignition occurs in Cell 4: the wind direction being west, and the inflow velocity being 6 m/s. Under the same conditions in Case 2-2, the inflow velocity is 2.0 m/s. These conditions assume that both the inlet and outlet of the coal storage tank are open, and the coal pile is 100% stored. In the case of spontaneous ignition, the concentration distribution analysis of carbon monoxide, a harmful gas in indoor coal storage sheds, was conducted, and the results are as follows. Figure 7 illustrates the results of the CFD analysis of carbon monoxide for spontaneous coal combustion in an indoor coal storage shed. For the inflow rate of 6.0 m/s, the ambient air flowed through the louver, and the flow circulated on the left side of the shed and inclined coal surfaces. In addition, carbon monoxide generated from the coal pile surface was only observed at the central wall and the point of spontaneous ignition. About 10.5 ppm of carbon monoxide was found in the upper part of the self-igniting cell. The ventilation volume was secured due to the increase in the inflow rate, and there was no  
Figure 5: Case description according to the mass flow rate. Figure 6: Ventilation rate of outside air inflow and outflow. area over 30 ppm (the hazardous standard concentration) in the workspace. As a result of checking the inflow rate of 2.0 m/s, it is possible to check the concentration of carbon monoxide in the upper part of the central shed. As the ventilation rapidly decreased, the accumulated carbon monoxide increased. An area where carbon monoxide exceeded 30 ppm occurs in the workspace was on the second floor, adjacent to the spontaneous ignition cell. The coal storage shed has three floors of workspace. The characteristics of the carbon monoxide concentration and exposure hazard areas were identified in each workplace. Figure 8 depicts the carbon monoxide concentration contour for each height. The result when the wind direction is a westerly wind of 1.0 m/s, which is the worst condition, must be checked to analyze the risk of carbon monoxide. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **Case 2-1** & **Case 2-2** \\ \hline Inlet wind speed & 6.0 m/s \\ Ignition point & Cell No. 4 \\ \end{tabular} & 2.0 m/s \\ Modeling & & \\ Coal pile & & 100\% (Fattened) \\ Boundary conditions & Louver & Window & Monitor \\  & & \\  & & \\  & & \\  & & \\  & & \\  & & \\ \end{tabular}
\end{table} 
Table 4: Computational fluid dynamics boundary conditions for analyzing hazardous gas concentration characteristics. Figure 7: Carbon monoxide concentration in a coal storage shed: front view for **(a)** 6.0 m/s wind speed; **(b)** 2.0 m/s, top view for the second-floor workspace; **(c)** for 6.0 m/s; **(d)** 2.0 m/s, and west view; **(e)** for 6.0 m/s; **(f)** for 2.0 m/s. It was assumed that the inlets and outlets for outside air were all open, such as the doors and windows. The analysis was conducted assuming that spontaneous ignition occurred in Cell 4. The first floor has many louvers and windows where outdoor air flows in. Therefore, the working space on the first floor did not have a dangerous space of 30 ppm or more carbon monoxide, due to the rise of carbon monoxide at the firing point. In the second-floor workspace, carbon monoxide was relatively high, compared with the surrounding area, because it was adjacent to the point of spontaneous ignition. In particular, up to 48.5 ppm of carbon monoxide concentration was identified on the two-layer central wall adjacent to the ignition point. As this increased, the carbon monoxide concentration gradually diluted. On the third floor, carbon monoxide was discharged into the monitor louver, and elevated carbon monoxide was diluted outside the inflow and outflow air, so no carbon monoxide concentration greater than 20 ppm was identified. However, this is the interpretation of spontaneous ignition conditions in one cell.