A noise survey is a measurement of what people are actually exposed to at work, expressed as a daily or weekly personal exposure rather than as how loud a machine is. The Control of Noise at Work Regulations 2005 set three thresholds, and which one you cross decides what you have to do: below the first, very little; above the third, you are in breach until exposure comes down.
The action and limit values
Regulation 4 sets the lower exposure action values at a daily or weekly personal noise exposure of 80 dB (A-weighted) and a peak sound pressure of 135 dB (C-weighted). The upper exposure action values are 85 dB (A-weighted) and a peak of 137 dB (C-weighted). The exposure limit values are 87 dB (A-weighted) and a peak of 140 dB (C-weighted), and unlike the action values the limit values may take account of the protection hearing protectors give.
What each threshold triggers
At the lower action values you must assess, provide information and training, and make hearing protection available on request. At the upper action values you must reduce exposure by means other than hearing protection so far as is reasonably practicable, mark hearing protection zones, enforce the use of protection, and provide health surveillance. The exposure limit values must not be exceeded at all.
When a survey is actually needed
When you cannot rule out the lower action values by simpler means. HSE's rule of thumb is that if people have to shout to be understood two metres apart, exposure is probably around 85 dB. If the answer is obvious in either direction you may not need measurement; where it is borderline, where you plan to rely on hearing protection, or where you need to defend a claim, you do.
Who may undertake a noise assessment
The regulations require the assessment to be made by a competent person. There is no licence, so competence is demonstrated rather than certified: knowing how to select and calibrate the instrument, how to sample a varying exposure over a shift, how to calculate daily and weekly personal exposure, and how to translate the result into control priorities. Membership of a professional body in occupational hygiene or acoustics is the usual evidence.
What a useful report contains
The measured levels by task and area, the calculated daily and weekly personal exposures by job role, the octave band data where hearing protection selection depends on it, the specific protection recommended with its real-world attenuation rather than the marketed figure, the priority order for engineering controls, and who needs health surveillance. A report that gives only area readings has not answered the legal question, which is about people.
Questions people ask about noise survey
What are the noise action values?
The lower exposure action values are 80 dB (A-weighted) daily or weekly personal exposure and a 135 dB (C-weighted) peak. The upper are 85 dB(A) and 137 dB(C). The exposure limit values are 87 dB(A) and 140 dB(C).
Does hearing protection count towards the limit?
Only for the exposure limit values. The lower and upper action values are assessed without taking hearing protection into account, which is why protection alone does not put you back below them.
Who can carry out a workplace noise assessment?
A competent person. No licence exists, so competence rests on demonstrable knowledge of measurement, exposure calculation and control, usually evidenced through occupational hygiene or acoustics qualifications.
How often should a noise assessment be reviewed?
When there is reason to suspect it is no longer valid or there has been a significant change, such as new machinery, a change in process, or a change in hours worked in a noisy area.