Fall of a tile

My apartment building's facade has the appearance of a red brick wall.  But in fact they're just tiles that look like bricks.  For security reasons, each of these tiles has a big ugly screw right on the middle of it.  From my apartment to the ground level is a good 18F fall, so this is a good measure.  Yet, just a few minutes ago I was sitting near my balcony, and I see one of these on the upper ledge of my balcony detach and drop.  I can even see that the tiles that had been right next to the fallen one are also a bit detached now.  How dangerous.