Was thinking about this last time I was in a filled customs/immigration hall waiting in line to be admitted to the United States...how would it be handled if there was some sort of (no foul play) emergency in the area? What if there was an electrical fire in one of the lights, something like that and a fire alarm sounded and everyone needed to evacuate...Is there a plan somewhere that would safely move potentially hundreds of people to a "sterile" area so they could then be legally admitted into the country?

This is really not country or airport-specific, and not meant to have anything to do with anything illegal or foul play, but just an honest to goodness accidental emergency...