Classification of Explosives When looking at conventional explosives there are two categories for explosives based on their detonation velocity, that is the speed at which the shock wave front travels through the explosive. According to the Department of Homeland security, high explosives detonate above 3300 fps whereas low explosives detonate below 3300 fps. An example of a low explosives (such as gunpowder) are characterized by their subsonic explosion created by the burning on the chemical. High explosives, when exposed to heat or shock then begin a self propagating heat producing decomposition. High explosives are then broken down into two further categories, primary and secondary explosives. Primary explosives are highly susceptible to shock and heat and as such are easy to set off. Secondary explosive however are relatively stable and require a primary explosive to be detonated in order to trigger their reaction. Outside of conventional explosives, there are thermonuclear devices. These thermonuclear devices are much more powerful than conventional explosives as they derive their power from nuclear reactions instead of stored potential chemical energy.