"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 said.
But, they did not know that when city, state and federal emergency responders arrived at the scene shortly after 2:00 p.m. Thursday.
A security guard under contract to the National Park Service reported finding a blue balloon filled with a white powdery substance at the entrance to the Liberty Bell Pavilion.
The area was quickly shut down and traffic on 6th Street between Market and Chestnut was blocked off.
"This is what we train for; this is what we practice for," Police Homeland Security Unit Deputy Commissioner Steve Johnson said.
Field tests conducted by the fire department's hazardous material unit indicated it was a biological agent and initially, authorities feared it may be anthrax.
The four security guards who came in contact with the balloon went through decontamination as a precaution, but they showed no symptoms of any 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 said.
Unknown to authorities at the time, a Food Network cooking show, 'Chefs Vs. City,' was taping a segment at Independence Mall earlier in the day. But officials say there was no cooking involved and its unknown if anyone associated with the show inadvertently dropped the deflated balloon filled with 3 or 4 ounces of flour.
Surveillance cameras at the Pavilion may ultimately answer the question.
"It's just too premature, we don't know what exactly happen, we will look at the film, we will review all aspects of the situation and we'll make a determination based upon the facts that are conveyed to us," Johnson said.
Meanwhile, the incident shut down Independence Mall and the Liberty Bell Pavilion for almost 5 hours.
At least one tourist from Colorado was unable to get to her car.
"We came back from the 'Duck Ride' right before it all happened, it had already blocked off the streets. We've been stuck here for at least 5 hours, so kind of interesting when you're touring," tourist Alisha Elliott said.
The powder was being taken to an FBI lab to be absolutely certain it was just flour, but authorities also add, there is no indication whatsoever that this was part of some kind of threat, and instead, was either a sick joke or just bad judgment on somebody's part.
