We were in north west air field, looking through the south jail house when a zombie came straight through the closed door, up the stairs, through the second closed door and attacked us. We killed one upstairs, heard more went to the stairs, more came in, killed them. Went down the stairs and killed the zombies as they came through the door. More and more times this happens. Especially at fire halls. All doors closed but they still get through. Also some just come through the wall under the stairs going up to the tower in the fire hall.