The exposure standard is 85dB for 8 hours. Louder than this it will become hazardous noise, yet it all depends on the amount of time the ear is exposed to the noise.
Therefore, 85dB over 9 hours is now considered hazardous noise.
The scale of time to levels of noise is not a linear scale but a logarithmic one. On this scale, an increase of 3 dB represents a doubling of sound energy. This means that every 3-dB increase can cause the same damage in half the time, yet peak noise levels greater than 140 dB(C), like a sledge hammering or a gunshot, will cause instantaneous damage. You can measure your decibel level to time with the table below. 85 decibels at 8 hours is the standard, noise levels exceeding this is taking your workers ears and workers compensation premium into harmful territories.
The facts above probably shock some of us just how delicate our ears are and how quickly permanent damage can be done. Hazardous noise affects the functioning of the inner ear, which can cause temporary hearing loss. After some time away from the noise, the ear can recover, however with further hazardous exposure the ear will lose its ability to recover and hearing loss can become permanent.
Active OHS can provide reports on particular tasks, grade of hearing protection required, as well as recovery time away from certain tasks to negate permanent hearing damage.