When Dana And Marty make it into the underground complex after they leave the elevator they find themselves in room with 8 (ish..) doors and some form of control booth. They go into the control booth and find "a big red button" with I believe the label Purge all or Purge system!
An army of nightmares, huh? Let's get this party started.
The result of pressing this button is that all the Monsters are release into the underground complex.
I can't think of any reason why you might have such a button in the control booth, can anyone supply me why the button exists?