‘Dirty bomb’ drill under way in Phila.

Don't be alarmed. This only a test.

About 700 officials, experts and responders from a range of federal, state and local agencies will take part in a 5-day drill starting today simulating the cleanup following a dirty bomb blast near Independence Hall.

"At some locations people can expect to see personnel in special protective clothing and workers simulating activities such as monitoring the air and collecting wipe samples from surfaces," the U.S. Environmental Protection Agency, the lead agency, said in a statement.

Dubbed Liberty RadEx, the drill portrays conditions a month after "a radiological dispersion device was detonated in Independence National Park," the EPA said.

It said the drill is unique in that it simulates the transition from the emergency phase of such an attack to the recovery phase.

"Our first concern is that the public understands Liberty RadEx is a drill and the activities people might see at different locations are only simulations of what might happen in a real event," EPA Regional Administrator Shawn M. Garvin said in a statement.

"This exercise is significant because it will help inform how all levels of government, businesses and community organizations can work together to meet challenges associated with long-term cleanup and community recovery from a dirty bomb attack," Garvin said.