There have only ever been two cases of caesium-containing bombs, and neither was detonated. Department of Defense's definition, which is 'the calculated use of unlawful violence or threat of unlawful violence to inculcate fear intended to coerce or to intimidate governments or societies in the pursuit of goals that are generally political, religious, or ideological objectives'. The meaning of terrorism used here, is described by the U.S.

Since the 9/11 attacks the fear of terrorist groups using dirty bombs has increased significantly, which has been frequently reported in the media.

Additionally, containment and decontamination of thousands of victims, as well as decontamination of the affected area might require considerable time and expense, rendering areas partly unusable and causing economic damage. For this reason dirty bombs are sometimes called 'weapons of mass disruption'. Its purpose would presumably be to create psychological, not physical, harm through ignorance, mass panic, and terror. Since a dirty bomb is unlikely to cause many deaths by radiation exposure, many do not consider this to be a weapon of mass destruction. Recent analysis of the nuclear fallout from the Chernobyl disaster confirms this, showing that the effect on many people in the surrounding area, although not those in close proximity, was almost negligible. A test explosion and subsequent calculations done by the United States Department of Energy found that assuming nothing is done to clean up the affected area and everyone stays in the affected area for one year, the radiation exposure would be 'fairly high', but not fatal.

At levels created from probable sources, not enough radiation would be present to cause severe illness or death. Though a radiological dispersal device (RDD) would be designed to disperse radioactive material over a large area, a bomb that uses conventional explosives and produces a blast wave would be far more lethal to people than the hazard posed by radioactive material that may be mixed with the explosive. It is however not to be confused with a nuclear explosion, such as a fission bomb, which by releasing nuclear energy produces blast effects far in excess of what is achievable by the use of conventional explosives. The purpose of the weapon is to contaminate the area around the dispersal agent/conventional explosion with radioactive material, serving primarily as an area denial device against civilians. A dirty bomb is a speculative radiological weapon that combines radioactive material with conventional explosives.

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