With the discretion of the director of personnel, vacancies in positions shall be filled, in so far as practicable by promotion from among employees holding positions in the classified service. Promotions shall be based upon merit and competition and upon the superior qualifications of the person promoted as shown by his or her records of efficiency. Upon receipt of a requisition for certification from an appointing authority, the director shall thereupon certify, to the appointing authority, the names of the three ranking eligibles from the most appropriate register, and, if more than one vacancy is to be filled, the name of one additional eligible for each additional vacancy. When the vacancy for which the appointing authority has requested a list of eligibles is that of a department head, the director shall certify to the appointing authority, for its selection, the names of six qualified candidates who apply, unless the appointing authority shall have requested the names of the three ranking eligibles only. However, in case of a vacancy in a position which requires peculiar and particular training and experience which, in the judgment of the board, may be properly acquired in the office or department in which the vacancy exists but not elsewhere, and it can be shown to the satisfaction of the board that there is in such office of department an employee who was regularly appointed and who is serving in a lower or different class or position following regular appointment, and whose familiarity with the duties of the position vacant and whose ascertained merit in performing or assisting in such work make it desirable for the best interests of the service to suspend competition, the board may, after a public hearing, approve the promotion of such employee, either without examination or with such tests or evidence of fitness as the board may see fit to require. Notice of the public hearing held under this section shall be given by mailing or delivering a copy of the notice to each governing body or appointing authority or department head affected, and by posting a copy of the notice publicly in the office of the board for at least three days prior to the hearing. All such cases shall be fully set forth in the minutes of the board. No suspension of competition for promotion authorized under this section shall be general in its application to such place or position and all such cases of suspension with the reasons for such action in each case shall be reported to the citizens supervisory commission at its next regular meeting. When promotional examinations are given, all employees who attain a passing grade shall have added to that grade one point for each year of service up to and including 20 years, irrespective of whether such service is continuous or not.