He clarified later in the thread.
A dirty bomb has to do with some sort of nuclear material like enriched uranium or any other hazardous radioactive material or waste combine that with explosives to spread the radiation and you have a dirty bomb. A dirty bomb will have a more emotional reaction than a physical. You can clean yourself from radiation and unless you ingest it in fatal quantities you can live through it.
Enriched urarium is no more hazardous than natural uranium or the depleted uranium used in sailboat keels and for armor-penetrating rounds.
Enriched Uranium is highly radioactive. Depleted Uranium used in munitions and sail boat keels is not.
Enriched uranium is uranium whose uranium-235 content has been increased through the process of isotope separation. Natural uranium consists mostly of the U-238 isotope, with about 0.7 percent by weight as U-235 which is the only isotope existing in nature to any appreciable extent that is fissionable by thermal neutrons. For use in commercial nuclear reactors natural uranium is enriched to about 3 percent U-235. Highly enriched uranium (HEU), which is used in nuclear submarine reactors contains at least 50 percent U-235, but typically exceeds 90 percent. Generally very high levels of enrichment are needed for nuclear weapons, as the presence of the U-238 isotope inhibits the runaway chain reaction that is responsible for the weapon's power.
During the Manhattan Project enriched uranium was given the codename oralloy, a shortened version of Oak Ridge alloy, after the plant where the uranium was enriched. The term oralloy is still occasionally used to refer to enriched uranium. The remaining U-238 with extremely low U-235 content is known as depleted uranium, and is considerably less radioactive than even natural uranium, though still extremely dense and is useful for armor penetrating weapons.
The ability to enrich uranium is of interest to those concerned about nuclear weapons proliferation.
For information on how uranium is enriched see isotope separation.