You're dropping context. I said: if you're a threat; the implied there is obvious: if you have a gun, knife, or similar weapon and pose an imminent danger in that regard.
Lethal force wouldn't be necessary in most circumstances to protect evidence unless the fleeing party is engaging in the use of lethal force. They can use force to protect government property, yes. Although most federal security officers aren't supposed to use firearms to attempt to disable vehicles.
It's relevant as an indication of the extent of their power on federal property, which you don't seem to understand at all.
You confused their security aparatus as being akin to private civilian security guards at a convenience store in regards to their power to detain / arrest / use force. For some reason you clearly thought "civilian" was similar to the context of a private corporation and didn't understand what federal powers would exist in that situation and on that property.
Define offense. Someone suggested it has to be criminal, but does it actually say that somewhere. Does disobeying an order to secure the room constitute an offense against NASA? Depending on the meaning of that word, it could certainly be interpreted that way, in which case arrest is a real possibility.
My guess is they'd arrest anyone who tried, and apologize later if someone proved that they shouldn't have done it. And nobody would actually be punished for the incorrect arrest.
Lethal force wouldn't be necessary in most circumstances to protect evidence unless the fleeing party is engaging in the use of lethal force. They can use force to protect government property, yes. Although most federal security officers aren't supposed to use firearms to attempt to disable vehicles.