One patient has been killed and three others suffered slight injuries in an explosion at Durham Regional Hospital in central North Carolina early Tuesday. No one else was hurt in the explosion on the hospital’s sixth floor around 2:15 a.m., said Katie Galbraith, hospital chief of operations. Officials were trying to determine exactly where the explosion occurred, Galbraith said. The hospital’s sprinkler system worked properly and the fire was controlled as about 30 firefighters arrived, Galbraith said. Other patients in the unit, a separately licensed facility operating as Select Specialty Hospitals, were moved to other parts of the hospital.