The law sets specific noise levels at which employers must take action. To manage noise risk, you need to understand how noise is measured, and what these action values mean.

In this module, you will learn about decibels, daily noise exposure, peak noise, and the three legal thresholds: the lower exposure action value, the upper exposure action value, and the exposure limit value.

By the end of this module, you will be able to:

• Explain how workplace noise exposure is measured.
• Explain why daily exposure depends on both loudness and time.
• State the lower and upper exposure action values.
• State the exposure limit value.
• Describe what the employer must do at each level.

Workplace noise is measured in decibels, written dB. Two scales are used:

• dB(A), or A-weighted decibels, which match the way the human ear responds to sound. Average noise levels over the day are measured in dB(A).
• dB(C), or C-weighted decibels, which are used to measure peak noise: the very loud, sudden bangs from impacts, presses or explosions.

Because the decibel scale is logarithmic, every increase of 3 dB doubles the sound energy.

So 88 dB(A) carries twice as much energy as 85 dB(A), and the time you can safely be exposed to it is halved. An increase of 10 dB means ten times the sound energy.

This is why a small reduction in noise can make a big difference to the risk.

The risk from noise depends on two things: how loud the noise is, and how long you are exposed to it.

Your daily personal noise exposure, written LEP,d, combines the two over a working day, as if it were averaged over eight hours.

A very loud task for a short time can be as harmful as moderate noise all day. Where exposure varies a lot from day to day, a weekly average can be used instead.

Each 3 dB rise halves the time it takes to reach the same daily exposure. For example, each of these gives the same daily exposure:

• 85 dB(A) for eight hours.
• 88 dB(A) for four hours.
• 91 dB(A) for two hours.
• 94 dB(A) for one hour.

So cutting the time spent on a very noisy task can reduce exposure just as much as making the task quieter.

The lower exposure action value is a daily or weekly exposure of 80 dB(A), or a peak sound pressure of 135 dB(C).

At this level, the employer must:

• Assess the risk to workers’ health.
• Give workers information, instruction and training.
• Provide suitable hearing protection to any worker who asks for it.
• Make hearing tests available where the assessment shows a risk to health.

The upper exposure action value is a daily or weekly exposure of 85 dB(A), or a peak sound pressure of 137 dB(C).

At this level, the employer must:

• Reduce exposure through a programme of technical and organisational controls, not just by handing out hearing protection.
• Designate hearing protection zones, where hearing protection must be worn.
• Make sure hearing protection is worn.
• Provide health surveillance, including regular hearing checks.

The exposure limit value is a daily or weekly exposure of 87 dB(A), or a peak sound pressure of 140 dB(C). This level must never be exceeded.

Unlike the action values, the limit value takes account of any hearing protection worn. It is the noise that actually reaches the ear. So the protection must be good enough to keep the noise at the ear below 87 dB(A).

Three key values decide what an employer must do:

• 80 dB(A), the lower exposure action value: assess the risk, inform and train workers, and make hearing protection available.
• 85 dB(A), the upper exposure action value: reduce exposure, mark hearing protection zones, make protection compulsory, and provide health surveillance.
• 87 dB(A), the exposure limit value, at the ear: must never be exceeded.
• The matching peak values are 135, 137 and 140 dB(C).