The principal office of the section shall be kept and maintained in Jefferson City, Missouri. In addition to the principal office in Jefferson City there shall be kept and maintained one branch office in the city of St. Louis, Missouri, and one branch office in Kansas City, Missouri, located in such quarters as may be designated by the director with the approval of the secretary of the labor and industrial relations commission of Missouri. Each of such branch offices shall be in charge of an assistant director of the inspection section and each such assistant director shall be empowered to do and perform in the name of the director any act which the director himself might perform, subject however to the supervision and approval of said director of the inspection section.