Smoke can trigger an asthma attack for me pretty easily. Simply walking down wind of someone actively smoking can cause problems with my breathing that can last quite a while after leaving.
Here it it is not permitted to smoke within 9 meters (about 27 feet) of building entrances and there is a $5000 fine for doing.
Some assholes still smoke at the doors and making it fairly difficult to just avoid it.
Walking down a crowded street? You bet I'm gonna breath in somomes smoke.