No person shall construct or maintain any basement, entrance or other opening in a through the public sidewalk, except that such entrance or opening be provided with substantial metal trapdoors, which when closed shall be flushed with the sidewalk, and which shall be kept closed at all times, except during the reception or delivery of goods, wares or merchandise. Efficient safeguards must be provided for the safety of the public during the time the cellar doors shall be open for the reception or delivery of goods, wares or merchandise. (Ord. 187 NCS §1 (part); prior code §21.5.)