A worker at the Obama Presidential Center in Jackson Park fell several stories down a ventilation duct and had to be extricated early Wednesday afternoon, according to the Chicago Fire Department. The man fell sometime after 1 p.m. Wednesday at the presidential center under construction in the 6000 block of South Stony Island Avenue. He sustained several injuries from the fall but was alert and conscious as he was being taken to University of Chicago Medical Center, authorities said. A spokesperson for the Lakeside Alliance, the group of construction companies building the center, said the company was aware of the incident and would release further information as it became available. A spokesperson confirmed that the U.S. Department of Labor’s Occupational Safety and Health Administration was also at the construction site but had no other information immediately available.