## 3 Results and Discussion
### Analysis of Explosion Residues  
Figure 12b shows post-explosion oil shale dust particles. Compared to the pre-explosion oil shale dust particles in Figure 12a, the post-explosion oil shale dust particles are fragmented in shape with developed pores. During the explosion of the oil shale dust, its volatile content was separated and participated in the combustion. After it combusted together with coke, the explosion residues were mostly inorganic skeletons such as SiO\({}_{2}\)  
Figure 11: Distributions of flame explosion pressure and flame propagation velocity of oil shale: (**a**) explosion pressure variation diagram; (**b**) flame propagation velocity diagram. Figure 12d shows post-explosion MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor particles. Compared to the unexploded MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor particles in Figure 12c, the exploded particles in Figure 12d were irregular in shape. The inhibitor particles were crushed under external forces; the NaHCO\({}_{3}\) originally coated on the MSA was thermally decomposed during the explosion. Hence, MSA skeletons could be detected in the post-explosion MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor. Figure 12e,f shows the explosion residues, in which the inhibitor particles and the oil shale particles were bonded and coated with each other. This inhibition effect can also be called a physical coating effect. Physical coating can effectively weaken the thermal radiation and thermal conduction of oil shale particles caused by heat sources in an explosion environment, thus reducing the heat of the oil shale particles and limiting the separation of the volatile content in the oil shale particles and the probability of the oil shale particles being ignited by external heat sources. The flame state of an oil shale dust explosion can also verify the coating effect in the suppression behavior of powder inhibitors on oil shale explosions. Figure 12: The SEM image of explosion residues after explosion inhibition. (**a**) Pre-explosion oil shale dust particles; (**b**) Post-explosion oil shale dust particles; (**c**) Pre-explosion MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor particles; (**d**) Post-explosion MSA-NaHCO\({}_{3}\) composite powder explosion inhibitor particles; (**e**) Post-explosion residue coating form1; (**f**) Post-explosion residue coating form2. In order to study the formation of reactive substances during explosions, the explosion products were collected following the 20 L spherical explosion experiment. The explosion products included gas and solid products. Gas products were collected with a gas collection device within 30 s after the explosion experiment. The composition of the gas after explosion was analyzed with a GC-MS-QP2010 Ultra, a Japanese SHIMADZU gas chromatography-mass spectrometry (GC-MS). Solid products were collected after the explosion test. The composition of solid products was detected with an EDX 4500H XRF tester produced by Skyray Instrument. The material composition of the main explosion products is tabulated in Table 6. The GC-MS analysis of the gas products showed that, for pure oil shale dust and the mixed dust with an inhibitor, the main gas products were CO2, NO2, CO, and SO2. After adding the 20% MSA-NaHCO3 composite powder inhibitor, the CO2 content in the gas mixture produced by the mixed dust explosion increased by 5.2% and the content of CO increased by 2.2%. As shown in Formula (1), the explosion suppression effect of the explosion inhibitor reduced the amount of oil shale dust participating in the explosion or made the combustion reaction insufficient, resulting in a lower CO2 content and a higher CO content. \[\mathrm{C_{n}H_{m}+2O_{2}\underset{\mathrm{underreaction}}{\rightarrow}C_{n-2 }H_{m-2}+CO+CO_{2}+H_{2}O} \tag{1}\]  
At the same time, as the NaHCO3 in the explosion inhibitor generated CO2 in the explosive environment, the CO2 content in the explosion products did not increase much, as shown in Formula (4).