Radiological dispersal devices (RDDs) use a conventional explosive to scatter radioactive materials, causing further damage and injury subsequent to the detonation. The actual harm caused by a RDD depends on the radioactive substance used and the dispersal mechanisms. If low-level radioactive sources were used, the primary danger would be the blast itself. Gauging how much radiation might be present is difficult when the source of the radiation is unknown; however, at the levels created by the most probable sources of radioactive materials, not enough radiation would be present in a dirty bomb to cause severe illness from radiation exposure. Depending on the quantity of material in the RDD, a detonated device would have a tendency to attenuate the radioactive concentration downwind of the site to fairly low levels quickly. The significant hazard would most likely be restricted to a radius of a few hundred meters surrounding a ground-level detonation. Depending on weather conditions, the incidence of localized areas of contamination further downwind is always a possibility. The primary difference between a radiation incident and a traditional hazmat incident is that radiation exposure can occur without direct contact with the source of radiation. This article explains the different types of radiation that have various penetrating abilities and present differing hazards. Regardless of the form or source of the radiation, however, energy is deposited in the body when the body is exposed to it. The amount of energy deposited by a radiation source depends largely on the energy of the radiation involved, its penetrating ability , and whether or not the source of radiation is located outside or inside the body. It is important for first responders to know how to measure external radiation levels from an incident that involves radiation. It is equally important to understand the dangers associated with various levels of exposure. The agency responsible for emergency response should develop policies regarding acceptable doses for emergency responders. These policies should be consistent with other risks normally encountered in the course of first responders' duties. This article presents a table of various radioisotopes that indicates for each radioisotope examples of uses, form for shipping, and mode of transport. 10 references