Whenever there are urgent reasons for filling a vacancy in any position of correctional officer and there is no list of persons eligible for appointment after a competitive examination, the appointing sheriff may nominate a person to the civil service commission for noncompetitive examination; and if such nominee shall be certified by the commission as qualified, after such noncompetitive examination and a medical examination, he may be appointed provisionally to fill such vacancy until a selection and appointment can be made after competitive examination in the manner prescribed in section eleven of this article; but the provisional appointment shall not continue for a longer period than three months, nor shall successive provisional appointments be made to the same position, under the provisions of this section.