# Development of Digital Device Using ZigBee for Environmental Monitoring in Underground Mines
## 4 Results
### Dust Measurement Result  
Fourteen dust measurement modules were numbered from D1 to D14, and the change in dust density after blasting was observed. Figure 8 shows the 1 min average trend of the measured dust density data for each module. Figure 8a shows the dust density of each module according to its standards. The larger the value, the redder it is, and the smaller the value, the greener it is. The measured value changes significantly in most modules before and after the blasting time. From approximately 4:40 pm, the blasting time, changes were detected from the D14 and D13 modules closest to the blasting point, and the dust density tended to increase sequentially in the direction away from the blasting point. Before the blasting began, the dust density decreased because the equipment was shut down and moved away from the blasting point. Figure 8b displays the dust density of all modules in color with the same standard. Modules farther from the blasting point (such as D1-5) have a low dust density, whereas modules closer to the blasting point (such as D11-14) usually have high values. In addition, the dust density increases earlier in the modules close to the blasting point.  
Figure 7: Graph of modules (**a**) V7, (**b**) V19, (**c**) V22, (**d**) V23, and (**e**) V26, where vibration was detected after blasting; and (**f**) graph of module V2 with missing data.  
The dust density variations in each module are shown in Figure 9. They were classified into three groups based on their installation location. After blasting, the dust density increased in all modules; however, over time, the dust density began to decrease in modules such as D11-14 (Figure 9c). In these areas close to the blasting site, the dust density gradually stabilizes over time after blasting. In addition, modules such as D1-3 showed a tendency for dust density to increase and then rapidly decrease (Figure 9a). Because these points are far from the blasting point, they are considered to be less-affected by dust and are well-ventilated areas. However, modules such as D5-9 show an increasing tendency in dust density owing to the slow influence of the blasting point.  
Figure 10 shows the results of visualizing the dust density measured in each module using ArcGIS Pro, a geographic information system software. The dust density values before and after blasting were shown at 5 min intervals, and the spatial distribution was predicted using the inverse distance weighting technique, an interpolation method. The dust density gradually increases even at a location away from the blasting point. The dust density increased immediately after blasting but slightly decreased over time. Owing to the short-monitoring time, there was no noticeable reduction in dust density. However, considering that the blasting occurred even before the start of monitoring, it was confirmed that the ventilation system was operating, and the dust density was relatively low.  
Figure 8: Measurement result of dust density. (**a**) Dust density change of each module and (**b**) distribution of overall dust density.  
Figure 9: Chart of changes in dust density over time for all the modules. (**a**) D1–4 modules, (**b**) D5–9 modules, and (**c**) D10–14 modules.