The director in accordance with the State Civil Service Act, Part 2 (commencing with Section 18500) of Division 5 of Title 2 of the Government Code, may appoint and fix the compensation of such clerical, inspection, investigation, and auditing personnel, as well as an assistant chief, as may be necessary to carry out the provisions of this chapter except as otherwise provided by Section 159.5. All such personnel shall perform their respective duties under the supervision and the direction of the chief.