Openings in sidewalks provided for in Section 24.65.010 shall be supplied with doors attached to a frame built into the sidewalk and shall be capable of supporting a load of 100 pounds per square foot. The door shall be constructed of sheet steel or other approved metal which has an approved non-slip surface. The dimensions of the door in any direction shall not exceed the dimension of the opening by more than 6 inches. The doors and frames shall be so constructed and maintained that there is no projection above or below the sidewalk exceeding 1/4 inch and existing doors which do not conform to the requirements shall be changed to conform within a period of 10 days after notice is given to change the same. Sidewalk doors shall be provided with a metal guard which, when the doors are open, will hold the doors open. This guard shall be located on the side of the sidewalk opening nearest the property line. The guard shall be made in the form of a grating with openings not exceeding 6 inches in dimension and so arranged that a child cannot get under or through the guard. This guard shall not be required for doors having metal gratings which are level with the sidewalk when the doors are open and the elevator platform is below the sidewalk level. Such gratings shall be capable of supporting a load of 100 pounds per square foot. Elevators having these sidewalk gratings shall be provided with a 3/4-inch steel bar to hold the doors open.