@matigo When they banned smoking in our building I would occasionally smell smoke and it took us about 3 months to figure out one of the professors was still smoking in his office with the door closed and the smoke was coming all the way through the vents to my office about 40-50 meters away. It made no sense that it wasn't bothering anyone in between but then we found out the ventilation system had a weird design where our (corner) offices were connected but those in between were getting ventilation from a different system of vents in the center of the building while ours were from vents on the outer edge.