Many years ago I when I was particularly young, I worked for a supplier where it seemed like everybody smoked, then this was back when you could smoke indoors; My bosses used to smoke like crazy in the section of the building where I worked, and but the thing was, even when our bosses were not near me, or if they were not smoking, I would still breath fresh smoke throughout the day.
This was because the Heating, Ventilation plus A/C plan in the building would be moving smoke from where other people were smoking who knows where, right to our nose, through the air ducts.
This would be whenever the heating or the air-conditioning went on, then and throughout most of the year you usually needed a single or the other of course, however forget an air quality system, this was the opposite of that, but i started getting a minor cough within weeks of laboring there. I used to smoke a little myself before I started laboring there. But that place cured me of ever wanting a cigarette again honestly soon. The need for air duct cleaning in that place was crazy; Nobody else noticed because they were smokers. The worst section is that you could not open the windows honestly much if at all occasionally, because all of us were high up in a skyscraper. So all of us were just stuck with this smokey air. I always thought I would quit a single day because of the bad air quality. I would go beach house occasionally plus I would feel sick from the air for hours. In the end, I left for a unusual reason, however when I left I was blissful never to breathe that air ever again.