When, in the opinion of the Code Official, there is imminent damage of failure or collapse of a building or structure which endangers life, or when any structure or part of a structure has fallen and life is endangered by the occupation of the structure, or when there is actual or potential danger to the building, occupants or those in the proximity of any structure because of explosives, explosive fumes or vapors or the presence of toxic fumes, gases or materials, or operation of defective or dangerous equipment, the Code Official is hereby authorized and empowered to order and require the occupants to vacate the premises forthwith. The Code Official shall cause to be posted at each entrance to such structure a notice reading as follows: "This Structure is Unsafe, and its Occupancy has been Prohibited by the Code Official." It shall be unlawful for any person to enter such structure except for the purpose of securing the structure, making the required repairs, removing the hazardous condition, or of demolishing the same. (109.1)