Explosives Experts

Terrorist attacks with improvised explosive devices on U.S. soil may be unlikely, but they are not impossible, administration officials and defense experts have said.

Department of Homeland Security officials, for their part, are assessing the vulnerability "underground locations" in the United States, and they need the help of a contractor to do so, according to a June 30 notice on the Federal Business Opportunities Web site.

The contractor's task will be to identify underground structures deemed particularly vulnerable to an IED attack, provide requisite training to security personnel, and figure out how many "Manhole Barrier Devices" it would take to block access to those sites.