Organized industrial labor in the early days was often very dangerous. Moreover, many of the workers did not know for how long they would work (in terms of hours per day) nor how long (in terms of the length of their "contract"). In the early days, there were a lot of accidents and medical help was needed for workers who worked in different industrial complexes, however, they were rarely given any.
Another hazard were different chemicals that were used at the time, but were later found to be unsafe, the workers at the time didn't know that it was dangerous to inhale or be near to, for example.