# Dust Dispersion Characteristics of Open Stockpiles and the Scale of Dust Suppression Shed
## 3 Results and Discussion
### Studied Cases
It has been suggested that, when dust concentrations reach 4 mg, the effect on human respiratory tract cannot be ignored. Therefore, we have studied the nearest distance from the center of the stockpile at which the dust concentration reaches 4 mg/m\({}^{3}\) at different wind speeds, which  
Figure 8: Variation of dust concentration with distance (9 m/s, 12 m/s, and 15 m/s). Figure 7: Variation of dust concentration with distance (4 m/s, 12 m/s, 16 m/s, and 25 m/s). we regard as the hazard distance, as shown in Figure 9. We simulated the dust dispersion under 13 kinds of wind speed conditions. We first obtained the distribution of dust concentration with distances as in Figures 7 and 8. Then, the hazard distances at different wind speeds for a concentration of 4 mg/m\({}^{3}\) are found in the graph. In Figure 9, the relationship between wind speed and hazard distance can be derived. At a wind speed of 12 m/s, the hazard distance achieved its maximum value, which is equal to approximately 63.5 m.  
The pattern of variation of concentration with wind speed is revealed in Figures 7 and 8, which is that the dust concentration at the same distance on the leeward side will show an increase and then a decrease with increasing wind speed. Therefore, we suspect that there are factors except wind speed that influence the particle concentration at lower altitudes. After analysis, the increase of wind speed will cause the dust to spread more into higher places. In Figure 10, the trends in percentage of particle mass over a range of heights from 0 to 3 m were compared for different distances and wind speeds. The percentage weight decreases significantly with the increase of wind speed at different distances (X = 50 m, X = 75 m and X = 100 m). This result is also clearly demonstrated in Figure 11. The more distant the location from the sand pile, the greater the decrease in occupancy with increasing velocity. In the range of 40 m to 50 m, the specific gravity drops quickly, indicating a significant dispersion of dust into higher space. At X = 50 m to 100 m, the specific gravity changes smoothly, and the curve can be approximated by the data points at 75 m and 100 m.  
We have determined the hazard distances for the stockpiles under the most unfavorable conditions, based on the analysis of the simulated data. However, it does not mean that the frame structure of the yard is square. When working on site, only the front and rear sides of the shed are open on all four sides, leaving the remaining two sides closed. Non-open sides are built with ventilated windows only. The wind blowing in through the small window can hardly act as a dust fugitive for the stockpile, so the distance between the two enclosed walls is not determined by the hazard distance. The structural design of the shed netting plays a very important role in the overall aspect ratio of the yard frame. Considering the structural stability and seismic resistance of the net frame, a two-way orthogonal diagonal release net frame was chosen. Moreover, considering the economical and two-way orthogonal structure of the mesh frame, a length to width ratio of 1.5 can be satisfied to all aspects. Figure 9: Minimum distance-wind speed. According to the analysis of hazard distances in the previous section of the article, a maximum hazard distance of 63.5 m was obtained. At a distance of 0-63.5 m from the center of the sand pile, under the most unfavorable wind conditions, it is dangerous to the human respiratory tract. We have defined this area as dust contaminated areas. At this point, the shed in the yard plays an important role. It stops the stockpiles from spreading to higher ground, and it also serves to stop non-staff from entering the dust contaminated areas of the yard. Herein, we chose the form of closure of the yard. The C-shaped structure has the advantage of high storage capacity per unit area (the surrounding retaining wall increases the maximum stack height of the stockpile).