On Wednesday, several of Philadelphia's first responders took part in a life-like drill to prepare for that very possibility.
The scenario: Terrorists have detonated a dirty bomb in the city of Philadelphia. There is damage and there are casualties.
Weeks later, the FBI discovers the site where the radioactive bomb had been assembled.
In this drill, that site is an unused hangar at the Boeing plant in Ridley Park.
"They need to make sure there are no explosives left, any hazardous or radiological material is contained, so that everybody is safe," said J.J. Klaver of the FBI.
FBI agents worked alongside officials with the US Environmental Protection Agency to play out this part of the drill.
They must collect evidence at the bomb-making site while ensuring that authorities, and the general public, are protected from any leftover radioactive materials.
"If there is a real life event that we're tied in well and everybody knows who's who and there's good communication across the board," said Obie Jones of Boeing.
Unlike a real situation, the participants in this "dirty bomb" drill are being allowed to take their time in securing any hazardous materials and gathering any clues. They are also gaining experience in dealing with different agencies.
The FBI wants to work out any kinks in its response plan now, rather than after the real thing happens.
"We need to be as careful as possible to protect the safety of the responders out here, to protect the safety of the public, and gather the evidence to build what would be a criminal case eventually," Klaver said.
This scenario is part of the larger "Liberty RadEx" Drill which tests the preparedness of several different governmental and law enforcement agencies - and the country's ability to recover from a dirty bomb attack.
