Said department may, from time to time, engage suitable persons to render sanitary service and to make or supervise practical and scientific investigations and examinations requiring expert skill and to prepare plans and reports relative thereto. All officers, persons, corporations or agents, having the control, charge or custody of any public structure, work, ground or erection, or of any plan, description, outlines, drawings or charts thereof, or relating thereto, made, kept or controlled under any public authority, shall permit and facilitate the examination and inspection and the making of copies of the same by any person authorized by said department; and the members of said department and such persons as are authorized by said department may, without fee or hindrance, enter, examine and survey all such grounds, erections, vehicles, structures, apartments, buildings and places.