High explosives may belong to different groups: primary explosives and secondary explosives. Primary explosives are very unstable and rapidly react to shock, friction, and heat. Any shock, friction, or heat makes primary explosives to burn or blast fast. Secondary explosives are much more safe to use and do not react very fast to shock, friction, and heat. Any shock, friction, or heat may burn such explosives, but not make them to burst and blast. Some people call secondary explosives as base explosives. Some people also tell about another group of explosives. These are tertiary explosives. These explosives do not react to shock, friction, and heat. For explosion, tertiary explosives may need a mixture with secondary explosives. 