No owner, agent, employee or other person shall open or remove, or permit anyone to open or remove the cover of any coal hole or grating in any sidewalk, or raise or permit anyone to raise any elevator or lift, or open or permit anyone to open the doors or other device covering any aperture in any sidewalk within the City, without first placing upon the sidewalk, all around the coal hole, elevator, lift, doors or other devices used to cover such aperture, a railing or other suitable structure or obstruction not less than three (3) feet high, and sufficient to protect and to warn foot passengers that the aperture is to be opened. During the whole time the aperture remains open it shall be protected by the railing, structure or obstruction, as stated herein and the railing, structure or obstruction shall be immediately removed when the aperture is closed.