In process installations, chemicals operate at high temperature and high pressure. Propylene is used as a basic raw material for manufacturing synthetic materials in the petrochemical industry; However, it is a flammable substance and explosive in the gaseous state. Thus, caution is needed when handling propylene. To prevent explosions, an inert gas, carbon dioxide, was used and the changes in the extent of explosion due to changes in pressure and oxygen concentration at 25 °C, 100 °C, and 200 °C were measured. At constant temperature, the increase in explosive pressure and the rates of the explosive pressure were observed to rise as the pressure was augmented. Moreover, as the oxygen concentration decreased, the maximum explosive pressure decreased. At 25 °C and oxygen concentration of 21%, as the pressure increased from 1.0 barg to 2.5 bar, the gas deflagration index (Kg) increased significantly from 4.71 barg·m/s to 18.83 barg·m/s.