The United Kingdom HSE's Controlling Noise at Work guidance book (L108) states that the normal methods for estimating the effectiveness of hearing protection are not suitable for high Peak levels.
Whenever Peak sound levels in excess of 137 dB(C) are measured the following process should be used in assessing the effectiveness of hearing protectors.
Sources of high peak noise levels can be split into three types, which are then used for the protector assessment:
LF - Low frequency peak noise
MF - Medium to high frequency peak noise
HF - High frequency peak noise
The table shows common process that produce high Peak sound levels, along with the LF/MF/HF categorisation.
Hearing protectors are provided with three values, called the H, M and L values. These are used in the normal hearing protector calculations, and are used differently for high Peak levels.
|Noise Source||Type||Typical Peak dB(C)|
|Nail gun / nailer||MF||130-140|
|Noise Source Type||Attenuation
|LF (low freq.)||L - 5|
|MF (medium freq.)||M - 5|
|HF (high freq.)||H|
This table is used to work out the attenuation of the hearing protector to high Peak sound levels. You use either the H, M or L figure from the protector's specification and modify it as shown.
This attenuation value is then subtracted from the measured LCPeak value (Peak sound pressure in dBC) to give an estimate of the level at the ear.
|Noise Source||Drop Forge - classified as having low frequency content, so LF|
|Hearing protector's HML figures||H = 20, M = 16, L = 15|
As the noise source is classified as LF, we use the L figure from the protector's attenuation figures and subtract 5 from it.
|Attenuation provided||L - 5 = 10|
|Estimated Peak level at the ear||129 dB(C)|