S.C. Code Ann. § 57-21-30

The terms of office of the commissioners so appointed shall be three years, two years and one year, respectively, from the date of their appointment and until their successors, who shall be appointed in like manner, shall have been appointed and qualified. They shall elect one of their number as chairman and one as secretary. In the event of a vacancy in the commission by reason of death, resignation or otherwise, such vacancy shall be filled for the unexpired term in the manner of the original appointment.