Which occupation has the highest incidence of occupational hearing loss?

Miners have the highest incidence of occupational hearing loss in the United States. 

Answer Extra: 

At least 80% of American miners are exposed to noise levels that exceed 85 dBA; 25% of these miners are exposed to noise levels higher than the 90 dBA Permissible Exposure Limit (PEL). Ninety-percent of all coal miners above the age of 50 have a hearing impairment. By the time coal miners retire, they are nearly guaranteed a moderate hearing loss.

source: 
R.J. Matetic. “Hearing Loss in the Mining Industry: Overview of the NIOSH Hearing Loss Prevention Program at the Pittsburgh Research Laboratory.”