Noise is the variation of air pressure comprising compressions and rarefactions of longitudinal waves. It is the magnitude of the compressions and rarefactions that determine the noise levels. As the noise level increases the risk of Noise Induced Hearing Loss (NIHL) increases.
A person can generally perceive a 1 – 3 dB change in noise levels. However the perceptions of noise levels are different to the actual energy that the ear is subjected. The perception of noise levels double every 10 dB, however the increase in energy experienced by the ear is doubled every 3dB. When it comes to the potential for noise induced hearing loss, it is the noise energy level that is critical. The noise energy levels considered to be excessive when noise levels exceed LAeq, 8hr of 85 dB(A) and LC,peak of 140 dB(C).
A general rule of thumb for detecting excessive noise levels is if you have to raise your voice when talking to someone 1 meter away. Some common noise levels include:
|140 dB|| Threshold of pain
Jet Engine at take off
|110 dB||Angle Grinder|
|100 dB|| Nightclub
|85 dB||Compliance A weighted noise levels for NSW WHS Regulations|
|80 dB||Alarm clock|
|75 dB||Vacuum cleaner|
|70 dB||Taking a shower|
|60 dB||Normal conversation|
|40 dB||Running water of a creek|
|20 dB||Leaves from the wind|
|10 dB||Pin dropping|
|0 dB||Threshold of hearing|
Noise levels can be steady state or impact. Steady refers to the continuous noise levels not varying by more than 6 dBa. Impact or impulse noise occur from a sudden peak in noise followed by an exponential decay which may cause acoustic shock.