Are the effects of NIHL on miners long-term?

Noise-Induced Hearing Loss (NIHL) is permanent and irreversible.

Answer Extra: 

One NIOSH study found that by age 50, about 90% of coal miners and 49% of metal/nonmetal miners had a hearing impairment (as compared with 10% of the non-occupational noise-exposed population). Simply stated, most miners have a hearing loss by retirement.

source: 
Hearing Loss in the Mining Industry: Overview of the NIOSH Hearing Loss Prevention Program at the Pittsburgh Research Laboratory