Cleaning of floors, walls and ceilings shall be done as often as necessary, but preferably during periods when the least amount of food is exposed, such as after closing. Only dustless methods of cleaning floors, walls and ceilings shall be used, such as vacuum cleaning, wet cleaning, treated dust mops or the use of dust-arresting sweeping compounds with brooms. Floors, mats, duckboards, walls, ceilings and attachments (e.g., light fixtures, vent covers, wall mounted fans and similar equipment), and decorative materials (e.g., signs and advertising materials) shall be kept clean.