18 Pa.C.S. § 503: Justification generally.

(a) General rule.--Conduct which the actor believes to be necessary to avoid a harm or evil to himself or to another is justifiable if:

(1) the harm or evil sought to be avoided by such conduct is greater than that sought to be prevented by the law defining the offense charged;

(2) neither this title nor other law defining the offense provides exceptions or defenses dealing with the specific situation involved; and

(3) a legislative purpose to exclude the justification claimed does not otherwise plainly appear.

(b) Choice of evils.--When the actor was reckless or negligent in bringing about the situation requiring a choice of harms or evils or in appraising the necessity for his conduct, the justification afforded by this section is unavailable in a prosecution for any offense for which recklessness or negligence, as the case may be, suffices to establish culpability.