# Dust Dispersion Characteristics of Open Stockpiles and the Scale of Dust Suppression Shed
## 3 Results and Discussion
### Studied Cases  
To provide a theoretical basis for the selection of the construction dimensions of enclosed frames for yards, the simulation is carried out by varying the magnitude of the inlet wind speed, while keeping other factors constant. Some researchers [32] carried out simulations at low and medium wind speeds, so only partial conclusions have been drawn. Some others [4] analyzed the total dust emissions at high wind speeds (15 m/s, 25 m/s, respectively), without analyzing the spatial distribution of dust. Figure 6 compares the distribution of particle concentrations in the lateral direction at different wind speeds and at two heights. It is clear that the maximum value of the concentration is around the coordinate z = 75 m. This is just downstream of the center of the pile, so that we only need to analyze the distribution of the longitudinal distribution of dust to obtain the boundary values of the dust concentration. Figure 7 demonstrates the variation of dust concentration with distance on the leeward slope of the sand pile for different wind speeds (25 m/s, 16 m/s, 12 m/s and 4 m/s, respectively). The wind speed mentioned refers to the wind speed at a height of 1.5 m, based on the height at which the wind speed was measured in the field. It can be seen that, at a height of 1.5 m, the particle concentration at different wind speeds shows a trend of rapid increase followed by a rapid decrease and then a slow decrease. The concentration increases because the sand particles are concentrated on the leeward slope of the pile by the wind. The decrease in concentration is due to the decrease in particle mass per unit volume as the spread of sand particles increases. Although the overall trend is similar for different wind speeds, the same location does not show a single trend in the change of particle concentration at different wind speeds. It can be found that particle concentrations are lower in the overall range for wind speeds of 4 m/s and 25 m/s. However, they are highest at wind speeds of 12 m/s. Therefore, we added the distribution of particle concentrations with distance from the stockpile at wind speeds of 15 m/s and 9 m/s in Figure 8. A similar pattern to the previous one was found, so that an inflection point should exist at around wind speed 12 m/s. At this wind speed, the concentration of dust reaches its maximum. Figure 5: Model validation versus the field measurements. Figure 6: Horizontal concentration distribution (4 m/s, 12.5 m/s and 16 m/s). The purpose of this study is to provide a theoretical basis for the size of the enclosed shed for the construction of the stockyard. We consider that there are two limiting conditions. Firstly, the dust reaches a certain concentration, which is harmful to human health. Secondly, the dust diffuses into the atmosphere, which is not environmentally friendly. With the addition of containment measures to the yard, most of the dust that pollutes the atmosphere is confined to the yard. Therefore, the impact of dust pollution on the environment is not strongly correlated with the size of the enclosed shed. It is the first constraint that has a major influence on the sizing of the shed. Studies on the evaluation of health risks associated with dust exposure showed that the impact of dust pollution on human health can be determined by the risk index \(R\) which can be calculated using Equation (11). We calculated the threshold value of \(C_{A}\) by assigning a value to the parameter. Below the threshold value, the effect of silica dust on human health can be ignored. In accordance with the relevant research, we assigned separate values to the parameters: \(IR=1\), \(EF=323\), \(ET=7\), \(ED=0.5\), \(BW=60\), and \(AT=182.5\). \(C_{A}\) can be calculated as 4 mg/m\({}^{3}\) using Equation (10). Therefore, when dust concentrations reach 4 mg/m\({}^{3}\), the dust exposure assessment index \(R\) exceeds the USEPA recommendation of \(10^{-6}\), and the effects on the human respiratory tract cannot be ignored.