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:
C-4 Ingredients
The explosive material in C-4 is cyclotrimethylene-trinitramine (C3H6N6O6), commonly called RDX (for "research development explosive"). The additive material is made up of polyisobutylene, the binder, and di(2-ethylhexyl) sebacate, the plasticizer (the element that makes the material malleable). It also contains a small amount of motor oil and some 2, 3-dimethyl-2, 3-dinitrobutane (DMDNB), which functions as a chemical marker for security forces.
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.
A U.S. Army unit detonated C-4 explosives inside this Serbian battle tank during Operation Joint Guard.
A detonator is just a smaller explosive that's relatively easy to set off. An electrical detonator, for example, uses a brief charge to set off a small amount of explosive material. When somebody triggers the detonator (by transmitting the charge through detonator cord to a blasting cap, for example), the explosion applies a powerful shock that triggers the C-4 explosive material.
When the chemical reaction begins, the C-4 decomposes to release a variety of gases (notably, nitrogen and carbon oxides). The gases initially expand at about 26,400 feet per second (8,050 meters per second), applying a huge amount of force to everything in the surrounding area. At this expansion rate, it is totally impossible to outrun the explosion like they do in dozens of action movies. To the observer, the explosion is nearly instantaneous -- one second, everything's normal, and the next it's totally destroyed.
The explosion actually has two phases. The initial expansion inflicts most of the damage. It also creates a very low-pressure area around the explosion's origin -- the gases are moving outward so rapidly that they suck most of the gas out from the "middle" of the explosion. After the outward blast, gases rush back in to the partial vacuum, creating a second, less-destructive inward energy wave.
A small amount of C-4 packs a pretty big punch. Less than a pound of C-4 could potentially kill several people, and several military issue M112 blocks of C-4, weighing about 1.25 pounds (half a kilogram) each, could potentially demolish a truck. Demolition experts typically use a good amount of C-4 in order to do a job properly. To take out one 8-inch (20.3-centimeter) square steel beam, for example, they would probably use 8 to 10 pounds (3.6 to 4.5 kilograms) of C-4. People apply C-4's explosive power toward all kinds of destruction. One common application is military demolition -- soldiers pack it into cracks and crevices to blow up heavy walls. It has also been widely used as an anti-personnel weapon, in battle and in terrorist attacks. In Vietnam, for example, soldiers used a number of C-4-based bombs and grenades. One notable weapon, the claymore mine, consisted of a C-4 block with several embedded ball bearings. When the C-4 was detonated, the ball bearings became deadly flying shrapnel (this sort of weapon was also featured in the movie Swordfish).
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.
This is the standard-issue plastic explosive used by the U.S. military. I recieved most of my early demo training in the army, which spoiled me for C-4. It retains its moldability over a wider range of temperatures, doesn't exude liquid (as does Semtex), and is pound-for-pound the most powerful explosive in common use. Its power, stability, and versatility are un- equalled. C-4 is in such demand and so well thought of that Muammar al- Quaddafi paid Edwin Wilson an exorbitant sum for 20 tons, even though he could get all of the Semtex he wanted on the open market for a much-lower price. With a few simple modifications, C-4 becomes even more versatile. If you mix 7 fluid ounces of mineral oil with a 1 1/4 pound bar, you get an exc- ellent paste explosive, roughly equivalent in power to TNT, and capable of sticking to almost anything. Sealed inside flat plastic bags, this mix can secreted in any number of useful spots (softsided luggage, for instance). One note of caution should be mentioned. With C-4 or any plastic explo- sive, the user should avoid mashing it when loading it into special devices or preparing charges. The sectional density of an explosive has a direct bearing on its power and velocity. The explosive packages are press-loaded to their optimum density for highest performance. This it not to say that they will not explode when used in this manner, but they will not utilize their full explosive potential. Sometimes commercial number 8 blasting caps will not detonate C-4, which was formulated for use with the more powerful J-2 military caps. In this case, two number 8s can be taped together, or some of its RDX can be extr- acted to use as a booster. To do this, a small lump (about 1 ounce) of C-4 is put into a cup of gasoline. The lump can be broken apart with a fork. Let it sit for an hour or so. The RDX should have separated from the plastic, which is soluble in gasoline, to form a white powder at the bottom of the container. This residue is filtered out of the gasoline and washed on the filter with a little more gas. Letting it sit overnight will evaporate any residual gas. Find a tube that will snugly fit the balsting cap and hammer one end closed. One or two grams of the RDX is pressed into the bottom of the tube, and the blasting cap is inserted and taped into place.
