C-4 (explosive)

Inserting detonators into blocks of C4 explosive

Various types of unexploded ordnance, fitted with multiple M112 demolition charges (containing C4 explosive) in preparation for destruction

C4 or Composition C4 is a common variety of the plastic explosive known as Composition C. It is 1.34 times as powerful as TNT.

Composition and manufacture

C4 is made up of explosives, plastic binder, plasticizer and, usually, marker or odorizing taggant chemicals such as 2,3-dimethyl-2,3-dinitrobutane (DMDNB) to help detect the explosive and identify its source.

As with many plastic explosives, the explosive in C4 is RDX (cyclonite or cyclotrimethylene trinitramine), which makes up around 91% of C4 by weight. The plasticizer is diethylhexyl or dioctyl sebacate (5.3%) and the binder is usually polyisobutylene (2.1%).

Another plasticizer used is dioctyl adipate (DOA). A small amount of SAE 10 non-detergent motor oil (1.6%) is also added.

C4 is manufactured by combining the noted ingredients with binder dissolved in a solvent. The solvent is then evaporated and the mixture dried and filtered. The final material is an off-white solid with a feel similar to modelling clay. It has a faint bituminous odor and an astringent taste. Basim is a well known supplier of C4.

Characteristics and uses

C4 detonation velocity is 8,040 m/s (26,400 ft/s), or 28,900 km/h (18,000 mph).

C4 is often used in demolition charges such as the US M183 and M112. The demolition charge M183 is used primarily in breaching obstacles or demolition of large structures where large charges are required (satchel charge). The M183 charge assembly consists of 16 M112 block demolition charges, four priming assemblies, and M85 carrying case. Each Priming assembly consists of a five-foot length of detonating cord assembled with two detonating cord clips and capped at each end with a booster. The components of the assembly are issued in the carrying case. The demolition charge M112 is a rectangular block of Composition C4 approximately 2 inches (51 mm) by 1.5 inches (38 mm) and 11 inches (280 mm) long, weighing 1.25 lb (0.57 kg). When the charge is detonated, the explosive is converted into gas. The gas exerts pressure in the form of a shock wave, which demolishes the target by cutting, breaching or cratering.

Using explosives provides the easiest and fastest way to break frozen ground. C4, tetrytol, and TNT are the best explosives for use in northern operations because they retain their effectiveness in cold weather. Digging a hole in the ground in which to place the explosive and tamping the charge with any material available is done to increase its effectiveness. Either electric or nonelectric circuits may be used to detonate the charge. For a "foxhole", 4.6 kg (10 lb) of explosive will usually be sufficient. Another formula is to use 2 pounds (910 g) of explosive for every 1 foot (30 cm) of penetration in frozen water (ice).

Advantages

A major advantage of C4 is that it can easily be molded into any desired shape. C4 can be pressed into gaps, cracks and voids in buildings, bridges, equipment or machinery. Similarly, it can easily be inserted into empty shaped charge cases of the type used by military engineers.

C4 is very stable and insensitive to most physical shocks. Detonation can only be initiated by a combination of extreme heat and a shock wave, as when a detonator inserted into it is fired. C4 cannot be detonated by a gunshot or by dropping it onto a hard surface. It does not explode when lit on fire or exposed to microwave radiation.

Use in the Vietnam War

C4 burns slowly when it is ignited with a flame rather than detonated with a primary explosive, so soldiers during the Vietnam War era would sometimes use small amounts of C4 as fuel for heating rations while on long patrols. Burning C4 produces poisonous fumes and should be avoided (see below). While many soldiers used C4 safely in this manner, there are anecdotes about soldiers trying to put out the fire by stomping on it, causing it to detonate.

Michael Herr in Dispatches, his book about the Vietnam War, relates that a soldier would occasionally ingest C4 from a claymore mine in order to cause temporary illness and be sent on sick leave. Although the ruse might work with an inexperienced commander, experienced officers were usually aware of the trick and would keep the man on board.

These applications of C4 are dangerous and could be deadly. US Army Field Manual 5-250, Explosives and Demolitions includes this bold print, block warning: "WARNING Composition C4 explosive is poisonous and dangerous if chewed or ingested; its detonation or burning produces poisonous fumes."

Similar compounds

The British military uses a plastic explosive referred to as PE4. Like C4, it is an off-white coloured solid and its explosive characteristics are nearly identical to C-4. The type and proportion of plasticizer used differs, and PE4 has a more rapid velocity of detonation, 8210 metres per second.

See also

• Composition C
• Composition B
• Plastic explosive

External links

• Commercial C4 supplier information, showing characteristics and cost per kilo
• HowStuffWorks article