weg vom Fenster sein

During the days that I visit my family in Western Germany, I have access to local TV. My dad is a history junkie, my granddad was a history teacher... you see, it runs in the family. We enjoy watching history documentaries. A couple of minutes ago I picked up an expression that I have known from little on, but never questioned its origin:

weg vom Fenster sein = to be away from the window???



In cololquial language it means to be dead. But not just dead, you actually noticed that this person just passed away. You do not say about your granddad that he is "weg vom Fenster". It is today more used as a warning: do not ... sonst bist du weg vom Fenster.

Origin
It comes from the mining business. Western Germany used to have a lot of coal mines in the Ruhr area (Duisburg, Essen, Dortmund, Herne, Bochum...). Many of those workers had lung problems, silicosis, due to their work below surface. Once sick, they would spend a considerable part of their day sitting at an open window. If you noticed a person everyday sitting at the window, you knew, he was sick with silicosis. But you also knew, when you stopped seeing him at the open window - away from the window - he had passed away. Er war weg vom Fenster.