Take it to the limit

How to treat hearing protection at the limit value in the Control of Noise at Work Regulations 2005

We recently had a question from a customer regarding the use of hearing protection to bring an employee’s noise exposure down to below the limit value. It is an interesting point and one that can get a little confusing.

There is a fundamental difference between the Lower and Upper Exposure Action Values (LEAV and UEAV) and the Exposure Limit Value (ELV) in that you are allowed to use hearing protection to comply with the ELV, but not the LEAV or UEAV. This means that an employee exposed to, say 83dBA Lep’d (daily exposure) so above the LEAV but below the UEAV, will remain in exceedance no matter what hearing protection they might be wearing, whereas someone else exposed to 94dBA Lep’d (above the ELV) can have that exposure reduced with the use of hearing protection. The trick is that you must demonstrate that this is the case with the use of a hearing protection assessment. In other words, you need to re-calculate the Lep’d exposure value with the hearing protection attenuation applied.

Without going into the detail here, there are three methods of assessing hearing protection; Single Number Rating (SNR), which is only a crude check and not ideal, the High, Medium, Low method (HML), which takes the frequency of noise into account so is a much better measure and Octave Band method, which is a more detailed analysis and will return the most accurate answer based on the frequency makeup of the noise. The detail of these methods is explained in the regulation guidance document from the HSE, L108.

Assuming you are going to use the HML or Octave method, which you should (that’s another discussion) then you will end up with an Assumed Protection Value (APV), which tells you what the expected noise level will be ‘inside’ the hearing protection, so what the worker will actually hear. Under normal circumstances, you take the ‘C’ weighted Leq or ‘A’ weighted Octave Bands, carry out the assessment and get the result, which will tell you the noise level at the ear (don’t forget the HSE 4dB real-world correction!). You then compare this to the HSE guide, which will tell you whether that APV is a good level of protection without over- or under-protecting.

If, however, you are dealing with someone exposed above the Limit Value, then you will need to know the actual exposure value at the ear. To do this, you carry out the hearing protection assessment in the same way, but the result you get will need to be further corrected for exposure time, just same as you calculated the exposure level in the first place.

If you want help with this, then there are some free tools available to do it. You can go to www.thecastlecloud.com, sign up for a free account and then use the free noise exposure calculators or you can go to the HSE website and download their free noise calculators.

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