Composite Compound 4 (often abbreviated to C4) is a kind of plastic explosive, which is often used in military operations. C4 is malleable: It can be given almost any form. It can also be handled safely, as neither fire, electricity nor shock will cause an explosion. C4 will explode if force and heat are combined. Because C4 can be given almost any form, additives are used, so that it can be detected more easily. Some of these additives have a distinctive odor, which can be detected by specially trained dogs. Another additive that is used often is metallic powder: This powder can be detected by metal detectors.