Under normal circumstances, noise below 85 decibels will not harm hearing, and noise above 85 decibels may be dangerous. Statistics show that the incidence of deafness increases obviously after working in a noise environment above 90 decibels for a long time.

If you work unprotected in a noisy environment for many years, the recovery of hearing sensitivity will be prolonged after leaving the noisy environment, and hearing will be restored after several hours or more. This loss that can restore hearing is called hearing fatigue.