High Explosives
High explosives have detonation rates above 3280 fps. Some dynamites, for example, have rates as low as 6000 fps, whereas some military explosives approach 28,000 fps. These explosives are designed to shatter objects and destroy them. The mechanism by which high explosives detonate is quite different than for low explosives. The latter are generally granular and at ignition, the burning travels from one particle to the next. Most high explosives, on the other hand, require a severe shock to get them to detonate. This can be accomplished using a blasting cap or a primary or initiating explosive. When these explode they create a strong shock wave that shatters the chemical bonds that hold molecules of fuel and oxygen together. Detonation takes place and this travels from molecule to molecule, picking up speed along the way so that the end result is practically instantaneous detonation. There are two types of high explosives: initiating (primary) and noninitiating (secondary).
Initiating high explosives Initiating high explosives are usually very powerful and very sensitive. Even the slightest shock or spark can be enough to cause detonation. For this reason, they are used only in very small quantities, usually to detonate less sensitive explosives in explosive trains. Examples include pure NG and mercury fulminate. Figure 1 shows chemical structures of some common initiating high explosives. Noninitiating high explosives These are explosives that are not sensitive and it usually takes a good deal of effort to cause detonation. These explosives can be easily transported and used without fear of accidental detonation. They are generally so insensitive that it takes a major shock, such as that supplied by a nearby initiating explosive in an explosive train, to get them to detonate. Examples include many dynamites and the military explosive, C4.
FIGURE 1 Structures of cyclotrimethylenetrinitramine (RDX), pentaerythritol tetranitrate (PETN), triacetone triperoxide (TATP) and trinitrotoluene (TNT). Note the large numbers of oxygen atoms that are part of the chemical structure of these materials. They react explosively and instantly with the carbon, hydrogen, and nitrogen atoms present, once the reaction is activated.
