years ago, most people didn't have any idea what C-4 was.
Recently, it has become an all-too-familiar term, popping up
and on television all
the time. In October 2000, terrorists used C-4 to attack the
U.S.S. Cole, killing 17 sailors. In 1996, terrorists used C-4
to blow up the Khobar Towers U.S. military housing complex in
Saudi Arabia. In December 2001, a man smuggled similar
material, hidden in his shoes, onto a commercial airliner. C-4
has also been used in many of the Palestinian suicide bombings
in Israel and the Israeli-occupied territories.
Photo courtesy U.S. Dept. of
A U.S. Army
officer plants 14 pounds of C-4 explosive on a command
In this edition of HowStuffWorks,
we'll find out what this powerful material is and see how it
can wreak such destruction.
The fundamental concept
behind explosives is very simple. At the most basic level, an
explosive is just something that burns or
decomposes very quickly, producing a lot of heat and
gas in a short amount of time.
Photo courtesy U.S. Department of
Soldiers set off
two C-4 charges on an air base runway during a training
operation. Like other high explosives, C-4's destructive
power comes from rapidly expanding hot
A typical explosive consists of some explosive material,
some sort of detonation device and, typically, some
sort of housing. The explosive material undergoes a rapid
chemical reaction, either a combustion
reaction, when triggered by heat or shock energy from the
In the chemical reaction, compounds break down to form
various gases. The reactants (the original chemical
compounds) have a lot of energy stored up as chemical bonds
between different atoms. When
the compound molecules break apart, the products (the
resulting gases) may use some of this energy to form new
bonds, but not all of it. Most of the "leftover" energy takes
the form of extreme heat.
The concentrated gases are under very high pressure, so
they expand rapidly. The heat speeds up the individual gas
particles, boosting the pressure even higher. In a high
explosive, the gas pressure is strong enough to destroy
structures and injure and kill people. If the gas expands
faster than the speed
of sound, it generates a powerful shock
wave. The pressure can also push pieces of solid material
outward at great speed, causing them to hit people or
structures with a lot of force.
C-4 is a high explosive designed for military use.
In the next section, we'll find out what sets it apart from
explosives, such as the propellant in a bullet
cartridge, the reaction occurs relatively slowly and
the pressure isn't as damaging. The expanding gases only
serve to push a small object. High explosives,
such as C-4 and TNT, expand more rapidly, generating
much greater pressure. Explosives experts refer to rapid
explosive reactions as detonation and slower
explosive reactions as deflagration.
What is C-4?
C-4, or composition 4,
is one variety of plastic explosive. The basic idea of
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
- It makes the explosive material highly malleable. You
can mold it into different shapes to change the direction of
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.
- RDX - 91 percent
- Di(2-ethylhexyl) sebacate - 5.3 percent
- Polyisobutylene - 2.1 percent
- Motor oil - 1.6 percent
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
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.
Photo courtesy U.S. Department of
A U.S. Army unit
detonated C-4 explosives inside this Serbian battle tank
during Operation Joint
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
For more information on C-4 and other explosives, check out
the links on the next page.
Lots More Information!
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