Was looking around for ways to clean egg off the house and saw an 'exit' sign post.... which peak my interest in this question that I have asked for years.
I've been in two fires. One in a dorm where someone's candle fell on LP records, another where a guys bed caught on fire. In both cases the black silky smoke that these fires created, especially that LP blaze, rose to the ceiling and completely blocked well lighted exit signs. You couldn't see a trace.
I've always thought that fire exit signs belonged on the floor. I've recently seen some there in Hotels. Is this code yet? Exit signs above the door are worthless in a fire, at least in my experience.