No one is liable to a penalty who, when violating a law or precept: 1° has not completed the sixteenth year of age; 2° was, without fault, ignorant of violating the law or precept; inadvertence and error are equivalent to ignorance; 3° acted under physical force, or under the impetus of a chance occurrence which the person could not foresee or if foreseen could not avoid; 4° acted under the compulsion of grave fear, even if only relative, or by reason of necessity or grave inconvenience, unless, however, the act is intrinsically evil or tends to be harmful to souls; 5° acted, within the limits of due moderation, in lawful self-defence or defence of another against an unjust aggressor; 6° lacked the use of reason, without prejudice to the provisions of cann. 1324 § 1 n. 2 and 1326 § 1 n. 4; 7° thought, through no personal fault, that some one of the circumstances existed which are mentioned in nn. 4 or 5.
Source: Code of Canon Law (Vatican.va)