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Hearing Protection for High Peak Sound Levels

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)
Punch press LF 115-140
Jolt squeeze LF 120-130
Explosives LF 150-160
Drop hammer LF 130-140
Drop forge LF 130-140
Nail gun / nailer MF 130-140
Hammer (metalwork) MF 130-150
Proof firing MF 135-140
Rifle fire MF 150-160
Fireworks MF >140
Pistol HF 140-155
Shotgun HF 150-160

Estimating the Peak Sound Level at the Ear

Noise Source Type Attenuation
Value (dB)
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.

Worked Example

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)