§ 261. Fire door. "Fire door" means a door constructed of such fire-resisting material as shall be specified in the rules of the board. The board shall determine and specify in its rules the materials and the manner of construction and erection of such doors, the sills thereof, and the automatic or self-closing device requirements of such doors. Electric contacts or interlocks of a type approved by the board may be accepted in lieu of self-closing devices on fire doors at each entrance to elevator or dumbwaiter hoistways.