How prevalent is hearing loss amongst miners?

Miners have the highest incident of noise-induced hearing loss amongst all occupations.

Answer Extra: 

Nearly 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). 

90% 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: 
Source: R.J. Matetic. “Hearing Loss in the Mining Industry: Overview of the NIOSH Hearing Loss Prevention Program at the Pittsburgh Research Laboratory.” http://www.msha.gov/30CFR/62.0.htm