C-4, or composition 4, is one variety of plastic explosive. The basic idea of plastic explosives, also called plastic bonded explosives (PBX), is to combine explosive chemicals with a plastic binder material. The binder has two important jobs:
- It coats the explosive material, so it's less sensitive to shock and heat. This makes it relatively safe to handle the explosive.
- It makes the explosive material highly malleable. You can mold it into different shapes to change the direction of the explosion.
To make C-4 blocks, explosives manufacturers take RDX in powder form and mix it with water to form a slurry. They then add the binder material, dissolved in a solvent, and mix the materials with an agitator. They remove the solvent through distillation, and remove the water through drying and filtering. The result is a relatively stable, solid explosive with a consistency similar to modelling clay.
Just as with other explosives, you need to apply some energy to C-4 to kick off the chemical reaction. Because of the stabilizer elements, it takes a considerable shock to set off this reaction; lighting the C-4 with a match will just make it burn slowly, like a piece of wood (in Vietnam, soldiers actually burned C-4 as an improvised cooking fire). Even shooting the explosive with a rifle won't trigger the reaction. Only a detonator, or blasting cap will do the job properly.
Unfortunately, C-4 will keep making headlines for years to come. Because of its stability and sheer destructive power, C-4 has attracted the attention of terrorists and guerilla fighters all over the world. A small amount of C-4 can do a lot of damage, and it's fairly easy to smuggle the explosive past light security forces. The U.S. military is the primary manufacturer of C-4, and it tightly guards its supply, but there are a number of other sources for similar explosive material (including Iran, which has a history of conflict with the United States). As long as it is readily accessible, C-4 will continue to be a primary weapon in the terrorist arsenal.