I feel like it's in the name: just like disaster responders operate in disaster, emergency rooms operate with patients in conditions of more or less emergency.

I feel like it's in the name: just like disaster responders operate in disaster, emergency rooms operate with patients in conditions of more or less emergency. Draw from a population large enough and you'll have a rolling supply of people encountering emergencies of varying degrees of urgency—plus people who worry that they're in an emergent condition but aren't trained to distinguish something critical from something worrying-but-not-urgent.