Fundamentally speaking, it is to control the combustion speed. If the combustion speed is too fast, the pressure will rise sharply, leading to an explosion. Mainly from the powder itself and combustion environment to control, first of all, to ensure that the powder has good shape and mechanical properties, so as not to make the burning surface increase rapidly when burning; In addition, the combustion pressure and temperature are controlled to prevent the combustion rate from increasing rapidly with the pressure. Of course, there are many details, so I won't go into them here.