Whenever there are urgent reasons for filling a vacancy in any position in a paid fire department and there is no list of individuals eligible for appointment after a competitive examination, the appointing officer may nominate an individual to the firemen's civil service commission for noncompetitive examination; and if such nominee shall be certified by the said 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 twenty of this article; but such 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.