## 3 Results and Discussion
### Introduction of Experimental Instruments
The isolation coating by the inhibitor on the oil shale particles during the explosion caused the particles to combust and become discrete. The flame length of oil shale dust reduced with increasing amount of slag-based composite powder in all cases. Under the effect of the MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor, the flame of oil shale dust was completely suppressed when more than 40% was added; the flame length decreased with the increase of the addition amount of composite powder explosion inhibitor in the range of 0-50%. The suppression effect of pure powder on the flame of oil shale dust was ranked as: NaHCO\({}_{3}\) > MSA. Figure 10: Flame suppression characteristics of explosion inhibitors for oil shale dust explosion in a semi-open space. Figure 9: Suppression characteristics of explosion inhibitors on the explosion pressure of oil shale dust in a 20 L closed space. According to the data measured by individual pressure sensors, taking the maximum pressure as the pressure value of that pressure wave passing through the measuring point, the discrete curve graphs of the explosion pressure variation of the mixed dust were generated, as shown in Figure 11a. After the oil shale dust was ignited, due to the large amount of reaction products generated by the oil shale dust, the combustion products were extensively released within a short time, thus creating a pressure inside the pipeline space. With the continuous advancement of the pressure, a pressure wave was formed. In the ignition stage, the pipeline pressure gradually rose and was acquired by pressure sensor 1 at 0.2 m. The pressure value at this point represented the maximum explosion pressure of oil shale dust: 0.46 MPa. As the explosion went on, the amount of shale dust involved in the explosion reduced. The explosion products decreased. The pressure released in the pipe space gradually dropped. The pressure wave was also weakened by the resistance of the pipe wall: the pressure measured by sensor 5 at 2.2 m dropped to 0.13 MPa. Adding explosion inhibitors to the shale dust slowed down its combustion reaction, limited the explosion participation of the shale dust, and reduced the reaction substances produced by explosion, thus bringing down the pressure value in the pipeline. The data show that 40% MSA-NaHCO\({}_{3}\) changed the maximum explosion pressure of the shale dust to 0.08 MPa and the maximum explosion pressure drop rate to 82.6%. In the experiment, a high-speed camera was used to acquire flame propagation images. The MATLAB program based on the Roberts operator was used to extract the edges of the dust flames. The flame propagation speed was obtained by changing the horizontal position of the flame front, as shown in Figure 11b. The pressure wave of the mixture began to gradually decrease as the explosion started. The initial flame propagation speed gradually increased. The flame propagation velocity reached its maximum near 0.75 m and then began to tend down. Furthermore, it can be seen that the maximum explosion pressure and flame propagation speed of the mixture significantly decreased after adding different mass fractions of MSA-NaHCO\({}_{3}\), and adding a 50% mass fraction of the MSA-NaHCO\({}_{3}\) mixture was able to completely inhibit the explosion of the oil shale dust.