Hearing Protection for
High Peak Sound Levels
The 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:
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LF |
Low frequency peak noise |
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MF |
Medium to high frequency peak noise |
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HF |
High frequency peak noise |
The table to the right shows common process that produce high
Peak sound levels, along with the LF/MF/HF categorisation. |
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Noise Source |
Type |
Typical Peak dB(C) |
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Punch press |
LF |
115-140 |
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Jolt squeeze |
LF |
120-130 |
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Explosives |
LF |
150-160 |
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Drop hammer |
LF |
130-140 |
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Drop forge |
LF |
130-140 |
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Nail gun / nailer |
MF |
130-140 |
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Hammer (metalwork) |
MF |
130-150 |
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Proof firing |
MF |
135-140 |
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Rifle fire |
MF |
150-160 |
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Fireworks |
MF |
>140 |
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Pistol |
HF |
140-155 |
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Shotgun |
HF |
150-160 |
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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.
Estimating the Peak Sound Level at the Ear
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Noise Source Type |
Attenuation
Value (dB) |
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LF (low frequency) |
L - 5 |
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MF (medium freq.) |
M - 5 |
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HF (high frequency) |
H |
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The table on the left 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 |
| Peak sound level LCPeak |
139 dB(C) |
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| 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) |
< Acoustic Terms Index
|
