permissible noise levels

The decibel (db) is the unit used to measure the intensity of a sound. The human ear hears sound pressures over a wide range. Decibels, which are measured on a logarithmic scale, correspond to the way our ears interpret sound pressures. Noise above 85 dB may result in hearing loss. This loss comes from both the intensity of the noise and the length of exposure to the noise. If you need to raise your voice to be heard, chances are that you are listening to sound at around 85 dB. Eight hours of exposure to higher levels at 90 dB can cause damage to your ears. Noise above 140 dB results in immediate, permanent damage and intense pain.