Unless otherwise clearly required by the context, as used in this Chapter:
(1) "Unavailable" means either that a vacancy in office exists, or that the lawful incumbent of the office is absent or unable to exercise the powers and discharge the duties of the office.
(2) "Emergency interim successor" means a person designated pursuant to this Chapter, in the event the officer is unavailable, to exercise the powers and discharge the duties of an office until a successor is appointed and qualified as may be provided in accordance with the constitution and statutes, or until the lawful incumbent is able to resume the exercise of the powers and discharge the duties of the office.
(3) "Attack" means any attack or series of attacks by an enemy of the United States causing, or which may cause, substantial damage or injury to civilian property or persons in the United States in any manner by sabotage or by the use of bombs, missiles, shellfire, or atomic, radiological, chemical, bacteriological, or biological means or other weapons or processes.
Acts 1963, No. 112, §3.