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The decibel is a logarithmic scale. It needs to be, so to encompass the enormous range between the smallest sound level that can be heard by the human ear, and the greatest level that can be tolerated. This can probably be more clearly understood by considering that the human ear has the ability at one end of the scale to detect a pin drop, and at the other a jet aircraft take off. Using a conventional scale i.e., 10 + 10 = 20, how many pins do think would you need to drop to create the same noise levels of that of the jet engine? Clearly this number would be so astronomically large to be impossible to manage effectively, hence the need for the logarithmic scale.


What about Multiple sound sources


Q. Would two machines be twice as loud as one? 


A. The two machines will be producing twice as much sound energy, but because of the way the ear responds this doubling of energy will only just be noticeable (3 dB).


Q. How much louder is the noise of ten identical machines than that of just one? 


A. The ten machines will be perceived as twice as loud as one machine, i.e., 10 dB louder


In terms of changes in sound level, the human ear can just about detect a sound level change of 3 decibels, and perceives an increase or decrease of 10 decibels as a doubling or halving of 'the loudness'.


Regulation 4 of the Control of Noise Regulations requires you to take specific action at certain action values.

These relate to:


the levels of exposure to noise of your employees averaged over a working day or week; and

the maximum noise (peak sound pressure) to which employees are exposed in a working day.


The two methods of measurement of noise levels are,


1.'A' weighting, written as 'dB(A), for average noise,  and

2.'C' weighting, written as 'dB(C)', for peak, impact or explosive noises,.


The values are:


for the lower exposure action values:

daily or weekly exposure of 80 dB (A - weighted)

peak sound pressure of 135 dB (C - weighted)


for the upper exposure action values:

daily or weekly exposure of 85 dB (A - weighted)

peak sound pressure of 137 dB (C - weighted)


There are also levels of noise exposure which must not be exceeded:


exposure limit values:

daily or weekly exposure of 87 dB  (A - weighted)

peak sound pressure of 140 dB (C - weighted)


Noise at Work

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