I think "with safety" is a pretty standard wording, but it looks like this has been our law since 1975. I'm digging around to see how it's been handled by our Supreme Court. I'll get some good quotes up in just a little bit, so that you can see how the contours of our duty to retreat have been drawn.
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.