77 Pa. Stat. § 431
Every employer shall be liable for compensation for personal injury to, or for the death of each employe, by an injury in the course of his employment, and such compensation shall be paid in all cases by the employer, without regard to negligence, according to the schedule contained in sections three hundred and six and three hundred and seven of this article: Provided, That no compensation shall be paid when the injury or death is intentionally self inflicted, or is caused by the employe's violation of law, including, but not limited to, the illegal use of drugs, but the burden of proof of such fact shall be upon the employer, and no compensation shall be paid if, during hostile attacks on the United States, injury or death of employes results solely from military activities of the armed forces of the United States or from military activities or enemy sabotage of a foreign power. In cases where the injury or death is caused by intoxication, no compensation shall be paid if the injury or death would not have occurred but for the employe's intoxication, but the burden of proof of such fact shall be upon the employer.
77 P.S. § 431