53 Pa. Stat. § 12629
Positions in the competitive class may be filled without competition only as follows: Whenever there are urgent reasons for filling a vacancy in any position in the competitive class, and there is no list of persons eligible for appointment after a competitive examination, the appointing officer may nominate a person to the civil service commission for noncompetitive examination, and, if such nominee shall be certified by the said commission as qualified after such noncompetitive examination, he may be appointed provisionally to fill such vacancy until a selection and appointment can be made after competitive examination, but such provisional appointment shall not continue for a longer period than three months. In every case the commission shall at once proceed to hold an examination and procure an eligible list.
When the services to be rendered by an appointee in the competitive class are for a temporary period not to exceed one month, and the need of such service is important and urgent, the appointing officer may select for such temporary service any person on the appropriate list of those eligible for permanent appointment without regard to his standing on such list. Acceptance or refusal of an eligible for temporary appointment shall not affect his standing on the register for permanent appointment.
Successive provisional or temporary appointments, either of the same or different persons, shall not be made to the same position. At the end of the three months period the office of the provisional employe, and at the end of the one month period the office of the temporary employe, shall be declared vacant, and it shall be the duty of the city controller and the city treasurer to prevent and decline to permit the payment of any compensation, salary, or wages to such provisional or temporary appointee for services rendered or claimed to be rendered after such periods respectively. No credit for experience gained during a provisional or temporary appointment shall be given to anyone in any examination.
53 P.S. § 12629