CHICAGO (CBS) — Firehouses around Chicago observed a moment of silence Sunday, in honor of their fallen colleagues, who died in the line of duty on Sept. 11, 2001.

They saluted the American flag at half staff.

Mayor Rahm Emanuel said the tragedy brought a sense of national unity. “The selfless act, where other people were running down this flight of stairs, ran up the flight of stairs to serve their fellow citizens.”

“It’s always in the back of your mind what happened back then,” a fire official said. Yeah, it happened in New York, but it could happen here also.”