As used in this chapter, the following terms shall have the meanings ascribed to them by this section:
(1) ATTACK. Any action or series of actions taken by an enemy of the United States resulting in substantial damage or injury to persons or property in this state whether through sabotage, bombs, missiles, shellfire or atomic, radiological, chemical, bacteriological or biological means or other weapons or methods.
(2) UNAVAILABLE. Absent from the place of session (other than on official business of the Legislature) or unable, for physical, mental or legal reasons, to exercise the powers and discharge the duties of a legislator, whether or not such absence or inability would give rise to a vacancy under existing constitutional or statutory provisions.