Kolkata: Four persons waiting in the out patient department (OPD) of the Calcutta Medical College and Hospital were injured after a chunk of concrete came off from the ceiling and fell on them Friday, police said. The incident happened in the waiting hall of the ophthalmology department’s OPD around noon. The four, after preliminary medical treatment, were released, police said. “Because the building is quite old, there are some rooms where the ceiling is not in good condition. We have closed the room,” a senior doctor at the hospital said.