Equivalent noise exposure levels

All noise levels in this table are the same as 85 dB(A) for eight hours.

In a noise assessment, you are comparing the person’s daily noise exposure to the limits set by the HSE in Noise Regs. These limits for assessing noise risk when looking at average noise levels are:

• The lower noise exposure limit is a daily or weekly noise exposure level of 80 dB(A)

• The upper limit for noise at work is a daily or weekly noise dose of 85 dB(A)

Generally, when people talk about the ‘limit for noise at work in a noise assessment’, what is being meant is that 85 dB(A) one.

That limit is not a one-off event, i.e. someone spending 10 minutes at 85 dB(A) in a noise assessment is not automatically meeting the 85 dB(A) legal limit. The ‘for eight hours’ bit in the Regs is important, some occasional higher noise is fine, the ’how long and how often’ is critical for assessing risk.

(There are also peak limits for quick ‘bang’ noises but I am not talking about those here - the limits there are 135 dB(C) and 137 dB(C), but we are talking about someone’s average noise exposure for a day here).

3dB means double the noise risk

As decibels are structured specifically to confuse people they are not linear, so 100 dB is not double the noise of 50 dB, and a 3 dB increase means a doubling of the noise risk, so 53 dB is double 50 dB. Told you it is designed just to confuse!

What that means in practice in a noise assessment is that for every 3 dB louder you get, the time people can spend safely in that noise halves.

The main noise limit is 85 dB(A) over eight hours, so double the volume is 88 dB(A), but as it has got twice as loud you can only spend half the time there, meaning four hours at 88 dB(A) is the same noise exposure risk as eight hours at 85 dB(A).

Basically, the faster you get the noise the shorter you can be there before it is too much.

Practical use in a noise assessment

If someone is in an area of 91 dB(A) for one hour but that is their only noise exposure in the day then they do not meet the 85 dB(A) limit, they would need to be there for two hours. That means things like hearing testing are not needed.

This is important in a noise assessment when looking at risks for people who do not spend all day in a high noise area but only go in occasionally, e.g. to walk through or to talk to someone.