A Health Hazard is something for which there is statistically significant evidence based on at least one study conducted in accordance with establishedscientific principles that acute or chronic health effects may occur in people exposed to its effects. One of the commonest, that most people know about is asbestos.
There was so much crap in my garage, by the time I got my car inside I had to Dukes of Hazzard my ass out of it because I couldn't open the door without hitting something!