Labor day is the first Monday of September, Labor Day is supposed to pay tribute to the contributions and achievements of the American workers. Labor Day gives workers a day of rest.
Labor Day is celebrated for the workers back then that worked all day and put in the tears blood and sweat into. These workers would have very limited breaks So the whole point of Labor day is so that the workers don't have to work that day.
The workers that were working at that time were working in the worst conditions you can work in, they had little exposure to clean air. The air in the building they were working in was bad air from all the the gasses and stuff. The day Labor Day became a holiday the workers had the rights to work in a safe environment.