By Tom Harris
C-4, or composition 4, is a type of plastic explosive. The key idea of plastic explosives, also known as plastic bonded explosives (PBX), is to combine explosive chemicals with a plastic binding material. The binder coats the explosive material, so it's less sensitive to shock and heat. This makes it relatively safe to handle the explosive. It also makes the explosive material highly malleable. It can be molded into different shapes to change the direction of the explosion.
C-4 contains the following: RDX - 91 percent; Di(2-ethylhexyl) sebacate - 5.3 percent; Polyisobutylene - 2.1 percent; Motor oil - 1.6 percent. The explosive material in C-4 is cyclotrimethylene-trinitramine (C3H6N6O6), usually called RDX ("royal demolition explosive" or "research development explosive"). The additive material is made of polyisobutylene, the binder, and di(2-ethylhexyl) sebacate, the plasticizer, which makes the material malleable). It also contains small amounts of motor oil and some 2, 3-dimethyl-2, 3-dinitrobutane (DMDNB), which functions as a chemical marker for security forces.
To make blocks of C-4, explosives manufacturers mix powdered RDX with water to form a slurry. They then add the binder material, dissolved in solvent, and blend the materials with an agitator. The solvent is then removed through distillation, and the water is removed by drying and filtering.
The result is a fairly stable, solid explosive with a consistency similar to modeling clay.
Because of the stabilizer elements, it takes a considerable shock to set off a chemical reaction in the C-4. Only a detonator, or blasting cap will do the job right. Once the chemical reaction is triggered, C-4 decomposes and releases a variety of gases (notably, nitrogen and carbon oxides). These gases expand at about 26,400 feet per second, which applies a huge amount of force to everything in the surrounding area. At that expansion rate, it is impossible to outrun the explosion; to an observer, the explosion is nearly instantaneous, although it actually has two phases. Initial expansion inflicts most of the damage. It also creates a low-pressure area around the explosion's origin; after the outward blast, gases rush back in to the partial vacuum, creating a second, less-destructive inward energy wave.
A small piece of C-4 packs a pretty big punch. Less than a pound of C-4 could potentially kill several people, and a handful of military issue M112 blocks of C-4, weighing about 1.25 lbs. each, could demolish a truck.
