Re: is to use/is to be used
Use this door for an emergency evaculation. -- Verbal instructions while giving a tour.
"Emergency Exit" -- sign on the door.
If you are not supposed to use that door otherwise: Use this door only for an emergency evacuation. "Emergency Exit Only"
If you are not suppposed to use any other door (which seem like a bad safety plan - what if it's blocked?): Use ONLY this door for an emergency evacuation.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.