Fort Worth fire investigators searched Tuesday for the cause of a large fire that gutted a vacant apartment complex, knocked out power to several hospitals and resulted in injuries to an Oncor utility worker.The 23-unit Wayside Plaza apartments in the 1700 block of West Cannon Street, on the near south side, had been vacant for about three months, said Steve Pezanosky, a lawyer for the property owner.The building had no active water, electric or gas connections, he said. People have been periodically checking on the property and, although there have been no reports of vagrants, you cant rule that out as a potential cause.The property was for sale and a deal was expected to close this week, he said, adding that it was his understanding that the buyer planned to raze the building.The cause of the fire was still under investigation and a dollar estimate of damages was not yet complete, Fire Department Battalion Chief Richard Harrison said Tuesday.The two-alarm fire was reported about 6 p.m. Monday. A utility worker was in stable condition after being hurt while trying to restore power to Fort Worths hospital district, which lost electricity as firefighters battled the blaze.An Oncor spokeswoman said Tuesday morning that the injured worker was conscious and talking and that his injuries were not life-threatening. "He is awake and talking," Oncor said on its Twitter feed.A loud crash was heard about 9:15 p.m. as a power line fell onto a fence on the west side of the complex, said Tim Hardeman, a Fire Department spokesman. The noise was accompanied by a huge flash, and lights in businesses, street intersections and homes suddenly went dim in the area near Eighth and Pennsylvania avenues. Workers restored power by 9:30 p.m.Power was cut to several hospitals, forcing them to rely on backup generators, Hardeman said.Texas Health Harris Methodist Fort Worth Hospital relied on generators from about 6 to 8 p.m. Monday, Megan Brooks, a hospital spokeswoman, said Tuesday.At that point, we worked with Oncor to get re-routed to a backup feeder until the problem could be resolved, she said. Patient care was not interrupted.At Plaza Medical Center of Fort Worth, the outage caused the cable television signal to go out in patient rooms and power was completely off at the Medical Plaza Professional building adjacent to the hospital, said Kathie Russell, director of organizational development and marketing.The professional building consists primarily of physician offices that were already closed for the day, she said. If the power had gone out in the main hospital, generators would have supplied electricity, she said.The lost television signal was possibly the fires biggest inconvenience to patients.When youre lying in a hospital bed, there often isnt a lot else to do but watch television, Russell said.