No picture? Then I will guess. Are your corridor walls white and there is so much light that they are rendering as 255 already? Atmosphere does not block the view to objects like real smoke. instead, it just adds some general glow and if your prop is already rendering as max white, there is nothing to add that would be visible.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)