The owner, lessee, agent and manager of every public building and every contractor involved shall provide such safe means for the cleaning of the windows and of exterior surfaces of such building as may be required and approved by the board of standards and appeals. The owner, lessee, agent, manager or superintendent of any such public building and every contractor involved shall not require, permit, suffer or allow any window or exterior surface of such building to be cleaned unless such means are provided to enable such work to be done in a safe manner for the prevention of accidents and for the protection of the public and of persons engaged in such work in conformity with the requirements of this chapter and the rules of the board of standards and appeals. A person engaged at cleaning windows or exterior surfaces of a public building shall use the safety devices provided for his protection. Every employer and contractor involved shall comply with this section and the rules of the board and shall require his employee, while engaged in cleaning any window or exterior surface of a public building, to use the equipment and safety devices required by this chapter and rules of the board of standards and appeals. The provisions of this section shall not apply to (1) multiple dwellings six stories or less in height located anywhere in this state; nor to (2) any building three stories or less in height in cities, towns or villages having a population of less than forty thousand; nor to (3) the windows or exterior surfaces of any building which may be exempted under any rule adopted by the board of standards and appeals. The board of standards and appeals may grant variations pursuant to the provisions of § 30 (Variations)section thirty of this chapter. All existing variations heretofore made by the board relating to the cleaning of windows are hereby validated and continued in full force and effect until amended or terminated by the board. The board of standards and appeals may make rules to effectuate the purposes of this section. Notwithstanding any other law or regulation, local or general, the provisions of this section and the rules issued thereunder shall be applicable exclusively throughout the state and the commissioner shall have exclusive authority to enforce this section and the rules issued thereunder.