You cannot render a functional weapon (blank firing or “real” or whatever you want to call it,) totally safe.
Which is why you should always treat them as something that will kill you given half the chance. (It was literally made to do just that.)
And you should always treat look alikes as if they were real because a) they’re easy to mistake for real ones and vice versa and b) the other people may not realize it’s a prop. (On a movie set, unlikely, but you never know who’s around and how they will respond. Or where an active shooter is going to appear.)
As for the cartridges, usually there’s tell tales of one sort or another. For dummy rounds it’s common to press the otherwise empty cartridge with a ball bearing or two so they rattle when shaken. Sometimes they also have a small hole on the wall of the casing
Blanks are, by their nature, lacking the bullet and the top is simply crimped to hold the wadding.
All it would have taken was a proper inspection to verify that it was unloaded/loaded with dummy rounds. Or, alternatively, Baldwin not pointing it at people.
Which leads me to the final thing you should always do: check the damn weapon. Don’t trust armorers. They’re people, too. They make mistakes, they fuck up.