Hey Ksail, if you are in imminent danger, protect yourself, if someone else is, you make the call, get out of there, as quickly as possible, I do not believe in threatening, it can elevate a situation, if it is time to shoot, then that's what it is, people dropping to the ground, will usually take the bravado out of the others, but don't linger, get out of there, if behind you was ok until you got there, then behind you is the direction that might be best, whether in reverse or doing a forced U turn, go go go.
If you are trapped in a building when this kind of event happens, be good friends with the security and ask them if they have a plan, if not come up with one, that protects you, I know you are working for the VA, so get to know the security force there, and know where to hide, since I'm sure you are not allowed to be armed while working. Get an improvised weapon, mop handle, or 2, scalpels, perhaps to bring with you in your hiding place.