Section 30. Pursuant to the provisions of this section, an appointing authority, upon submission of a requisition, may make a promotional appointment within a departmental unit of a permanent employee in the labor service to a position in the lowest title, as determined by the administrator, in the official service in such departmental unit upon certification from an eligible list established as the result of a competitive examination. Except as otherwise provided in this section, eligibility to take such examination shall extend only to civil service employees in such departmental unit who have been employed in such unit after certification and in a permanent status for at least one year next preceding the date of the examination. The administrator may restrict such eligibility to any title or titles in the labor service of such departmental unit if he determines that the number of employees in such title or titles is sufficient for the holding of a competitive examination, and he may, in his discretion, extend such eligibility to any title or titles in the official service in such departmental unit.

A permanent civil service employee in the labor service may be promotionally appointed within a departmental unit, with the approval of the administrator, to a position in the lowest title, as determined by the administrator, in the official service of such unit provided that such employee has been employed in such unit after certification and in a permanent status for at least one year, is the first, second, or third ranking employee in length of service in the unit who is willing to accept the promotional appointment, and shall demonstrate, by the passing of an examination prescribed by the administrator, that he possesses the qualifications and abilities necessary to perform the duties of the position. The determination as to which employees are willing to accept such appointment or promotion shall be made after the posting of a promotional bulletin in accordance with the provisions of section twenty-nine; provided, that for the purposes of making said determination eligible employees in the official service in said departmental unit shall be entitled to respond to the bulletin, and those who do respond shall be considered in making the determination.

The provisions of this section may, upon the request of the appointing authority and at the discretion of the administrator, be applied to a departmental unit in which only titles in the official service are subject to the provisions of the civil service law and rules. In such case, eligibility to take a competitive examination pursuant to this section shall extend to employees in the departmental unit in titles approved by the administrator who have been employed therein on a full-time basis for at least one year next preceding the date of examination, notwithstanding the fact that they have been employed in positions which are not subject to the provisions of this chapter, and such employees may be appointed upon certification from the list established as the result of such examination. The length of service of any employee who is initially appointed to a civil service position pursuant to the provisions of this paragraph shall, for purposes of computing seniority under section thirty-three, be deemed to begin on the date of his first employment as a permanent employee in such position.