Firefighters freed an injured construction worker trapped for hours under tons of concrete Tuesday after part of the city's old convention center abruptly collapsed during demolition work.

Casey Johansen, 28, was conscious and talking during the ordeal, said Mike Sandulak, a Fire Department division chief. He was taken to the hospital.

On Tuesday night, doctors had determined that Johansen suffered only one broken bone — a femur. He was sedated and on a ventilator at a hospital.

Doctors earlier had thought they may have had to amputate his legs. Surgeons were able to restore the blood flow to his legs, said Dr. Steven Reinhart, who was on call with the fire department.

More than 100 firefighters from Phoenix and nearby agencies worked for more than six hours to pull Johansen from the debris. Firefighters shored up the structure with wood and air bags and cut reinforcing rods in the concrete so they could remove it.

As Johansen awaited rescue, firefighters gave him painkillers and started intravenous lines so they could give other medications and fluids. Medical personnel in hospital scrubs and hard hats passed oxygen bottles and IV fluids into a hole.

"I have not seen a rescue like this in Phoenix — this complicated," said Fire Chief Bob Kahn.

Johansen's father, who was working at the site, and his wife were allowed to talk to him and hold his hand until he was rescued. His mother, in-laws and siblings also were at the scene.

"Certainly they're concerned and worried, but they're strong," Mayor Phil Gordon said.

The accident happened before daybreak during demolition work on the old Civic Plaza when part of the structure's Grand Entrance collapsed as Johansen was operating a front-end loader. The plaza, once home to conventions and trade shows in Phoenix, is being replaced.

The cause of the accident was under investigation.