71 Pa. Stat. § 779.5
All State officers, subject to such regulations as the Governor (or other official authorized under the Constitution and this act to exercise the powers and discharge the duties of the office of Governor) may issue, shall, upon approval of this act, in addition to any deputy authorized pursuant to law to exercise all of the powers and discharge the duties of the office, designated by title emergency interim successors and specify their order of succession. The officer shall review and revise, as necessary, designations made pursuant to this act to insure their current status. The officer will designate a sufficient number of such emergency interim successors so that there will be not less than three such deputies or emergency interim successors, or any combination thereof, at any time. In the event that any State officer is unavailable following an attack, and in the event his deputy, if any, is also unavailable, the said powers of his office shall be exercised and said duties of his office shall be discharged by his designated emergency interim successors in the order specified. Such emergency interim successors shall exercise said powers and discharge said duties only until such time as the Governor under the Constitution or authority other than this act (or other official authorized under the Constitution or this act to exercise the powers and discharge the duties of the office of Governor) may, where a vacancy exists, appoint a successor to fill the vacancy or until a successor is otherwise appointed, or elected and qualified as provided by law, or an officer (or his deputy or a preceding named emergency interim successor) becomes available to exercise or resume the exercise of the powers and discharge the duties of his office.
71 P.S. § 779.5