(1) In case of vacancy in a position requiring peculiar and exceptional qualifications of a scientific, professional or expert character, upon satisfactory evidence that competition is impracticable and that the position can best be filled by the selection of some designated person of recognized attainments the board may, after public hearing and by the affirmative vote of all members suspend competition, and all such cases of suspension shall be reported together with the reason therefor, in the annual reports of the commission.

(2) Vacancies occurring in the merit system classification of any county shall be filled by promotion insofar as possible. A promotion shall be made only after an open competitive examination, admission to which shall be limited to merit system officers. Such examination shall include an average of service ratings for the next preceding year, a rating of seniority, and test the competence of the peace officer to perform the duties required in the position for which application is made. The combined weights of service rating and seniority shall be not more than 40% of the whole examination. Succeeding vacancies shall also be filled by promotion until the lowest grade is reached, which grade shall then be filled from the eligible list as herein set forth.

(3) After a promotional examination, the commission shall prepare a promotional register which shall take precedence over an eligible register. Certification therefrom shall be made in the same manner as from an eligible register.