Anthrax scare at Philadelphia's Liberty Bell

A security guard at Philadelphia's Liberty Bell Pavilion reported the discovery of a blue balloon that was filled with a white powdery substance on Thursday, setting off fears of a potential bioattack.

The discovery of the balloon at the entrance to the Liberty Bell Pavilion led to the area being shut down, with traffic on 6th Street between market and Chestnut blocked off.

"This is what we train for, this is what we practice for," Steve Johnson, Police Homeland Security Unit Deputy Commissioner, told WPVI-TV.

Initial field tests conducted by the fire department's hazardous material unit said that the powder was a biological agent, with authorities fearing it was anthrax.

As a precaution, the four security guards who had come into contact with the balloon were decontaminated, though none showed symptoms of exposure.

"This wasn't an exercise; we're handling it as a hazardous material incident until we know exactly what the substance was," FBI Special Agent J.J. Klaver told WPVI-TV.

Further testing revealed that the balloon was actually filled with a wheat-based flour.

"Multiple protein tests were performed and we are comfortable that the powder is a flour base," Deputy Chief Edwin Grugan of the Philadelphia Fire Department told WPVI-TV.

"Chefs Vs. City," a Food Network cooking show, had taped a segment for its show earlier in the day at Independence Mall, though officials say that no cooking took place and do not know if anyone associated with the show dropped the balloon inadvertently.