Texas Natural Resources Code - NAT RES § 40.204. Defenses

(1) an act of war or terrorism;

(2) an act of government, either state, federal, or local;

(3) an unforeseeable occurrence exclusively occasioned by the violence of nature without the interference of any human act or omission; or

(4) the wilful misconduct or a negligent act or omission of a third party, other than an employee or agent of the person responsible or a third party whose conduct occurs in connection with a contractual relationship with the responsible person, unless the responsible person failed to exercise due care and take precautions against foreseeable conduct of the third party.