In 1941 Adolf Hitler ordered a directive intended to suppress members of the resistance. It was called Nacht und Nebel ("Night and Fog"). People suspected of "offenses against the Reich" would disappear without any trace.
Who could be considered suspect? "anyone endangering German security" (die deutsche Sicherheit gefährden).
The public safety exception is a very specific exception. Let's say you're a cop who just caught a guy who has rigged a building with bombs and you ask him where the bombs are and how to disarm them. If he tells you and incriminates himself before being mirandized that's still kosher. That's the public safety exception. Period.
If you ask him "why did you do this", and you haven't mirandized him yet and he confesses right then but recants later, you dun fucked up.