You are one of the remaining Black Mesa personal left after the Resonance Cascade, nearly all other personal being killed by those aliens from Xen, and unfortunately for you the exit you were trying to reach for hours is locked, as you loose hope of ever making it out alive the door suddenly explodes, and what appear to be four soldiers come in, it must be the soldiers that one of the surviving security officers mentioned are coming

Demolition Expert: "Man i just the smell of explosions"

Squad Leader: "Stay alert people!"

Grunt: "Roger that sir"

Shotgunner: "Yes sir"

As you think of running towards them to get rescued, you see a scientist run towards them, before getting shot down

Shotgunner: "Got one!"

Grunt: "Hey i wanted to have the first kill!"

Seems like the marines aren't here to save you and the staff like you thought, instead it seems like they're here to silence everyone