At O'Hare International Airport, teams of Chicago police, fire and aviation officers arrived at the C concourse of Terminal 1, followed by FBI and Transportation Safety Administration agents, to respond to a report of a small explosion.
A baggage handler unloading cases of equipment from a jetliner was injured slightly when authorities say a battery short-circuited, overheated and began to disintegrate.
The I-Team learned the exploding battery was inside one of several cases of industrial testing equipment that had been checked by employees of a private engineering firm traveling to Chicago.
"It was a little scary to pull up and see what was going on," said United passenger Walter Reinthaler. "There were probably six or seven big fire trucks... looked like a mobile command unit. There were probably 20 or 25 police cars out there on the tarmac."
As that incident was drawing attention, federal homeland security officers and Chicago police had cordoned off a street in the South Loop near where a suspicious package had been found.
The package, in or near a postal box, was by the Metro Correctional Center, the federal prison facility that houses nearly 700 prisoners, many of who are considered extremely dangerous.
Until mid-afternoon, Van Buren Street was closed from the MCC for several blocks to the east to the Dirksen Federal Building, where many prisoners are transferred to court each day.
Among the high-risk prisoners is Jesus Vicente Zambada-Niebla. Chicago prison officials have kept Zambada-Niebla in solitary confinement for the past 18 months, not even allowing him onto the roof for exercise, saying they feared that as the underboss of the ruthless Sinoloa drug cartel in Mexico, he was both an escape risk and an assassination target.
Federal law enforcement agencies and local police prepare and train for days like Tuesday and allocate resources to be able to handle two potentially serious situations in far reaches of the city.
At O'Hare, the small explosion was ruled an accident, said Rosemarie Andolino, commissioner of the Chicago Department of Aviation.
"The biggest thing here is that [there was] no criminal activity," she said. "The public is not nor was in any danger. It was an accidental issue. It's an isolated issue. It's being dealt with and [it's] business as usual."