The Control of Noise at Work Regulations 2005 hang on a small set of numbers. Understanding them tells you exactly what the law expects at your site. Two things are measured: daily or weekly personal noise exposure, written LEP,d and measured in dB(A), and peak sound pressure, measured in dB(C) for sudden, impulsive noise.
The three thresholds
| Value | Daily exposure (dB(A)) | Peak (dB(C)) | What it triggers |
|---|---|---|---|
| Lower action value | 80 | 135 | Provide information & training; make hearing protection available on request. |
| Upper action value | 85 | 137 | Take action to reduce exposure; hearing protection becomes mandatory; mark Hearing Protection Zones; health surveillance. |
| Exposure limit value | 87 | 140 | Must not be exceeded, taking account of the protection the hearing protectors provide. |
Why exposure, not just loudness
A level on its own does not decide the risk — how long someone is exposed matters just as much. Exposure is energy over the working day, so a very loud task for a short time and a moderately loud one all day can land at the same daily figure. That is why the assessment measures by area and by role rather than quoting one number for the whole site.
The exposure limit value is different
Unlike the action values, the 87 dB(A) / 140 dB(C) limit is assessed taking hearing protection into account — the level actually reaching the ear must not exceed it. If it does, exposure has to be reduced immediately.
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