This stuck in my head awhile, until I found myself browsing laws for PA. This is what I came up with -
The use of deadly force is not justifiable under this section unless the actor believes that such force is necessary to protect himself against death, serious bodily injury, kidnapping or sexual intercourse compelled by force or threat; nor is it justifiable if:
....the actor knows that he can avoid the necessity of using such force with complete safety by retreating or by surrendering possession of a thing to a person asserting a claim of right thereto or by complying with a demand that he abstain from any action which he has no duty to take, except that:
(A) the actor is not obliged to retreat from his dwelling or place of work, unless he was the initial aggressor or is assailed in his place of work by another person whose place of work the actor knows it to be;[line]
I'm not a lawyer. Please read the full text in the link below and talk to somebody with a legit law degree!