Control of Noise at Work Regulations
Article Index
Control of Noise at Work Regulations
Daily Exposure
Hearing Protection Assessment
New Levels
Health Surveillance
Conclusions and Further Reading
Page 3 of 6

Hearing Protection Assessment

It has always been the case that the use of hearing protection should be a last resort after noise control measures have been taken as far as reasonably practicable. Even so, many employers still provide them and need to be able to produce evidence that the correct protection has been selected for each application or task. Existing regulations and the new proposed draft both give 3 methods for evaluating hearing protection in the workplace. These are Single Number Rating (SNR), High Medium Low (HML) method and Octave Band selection.

GA131M Octave Band and Third Octave Band Sound MeterAll the methods of assessing the effectiveness of hearing protection are based on using data supplied by the manufacturer of the defenders. The Single Number Rating is an estimate of the average, overall protection offered by a particular plug or muff etc. The problem is that ear defenders work considerably better at stopping high frequency sound than they do with low frequencies, so if the noise in question is predominantly low frequency, then it is easy to under estimate the amount of protection and over expose the employee. Great care should be exercised when using this method.

The HML assessment method uses a measurement of both the ‘A’ and ‘C’ weighted sound levels to give some indication of the amount of low frequency noise present. Using a simple formula and table, which is described in the 1989 guidance notes, a slightly more accurate prediction can be made. Simple sound meters such as the Castle GA215 or GA113 can give an 'A' weighted and 'C' weighted level as an Leq, so the SNR or HML methods can be adopted.

Octave Band Graph
Figure 2
The best method of all is to measure the Octave Band frequency levels and use the table provided by the manufacturer (the one on the packet that had little meaning until now!). The octave band measurement gives a fairly detailed breakdown of the level of noise at various frequencies, so when the manufacturers' data is applied, a much better picture will emerge of the effectiveness of the hearing protection device. Figure 2 shows a measured octave band in red and protected levels at the ear in green. The table in figure 2 shows the overall SPL (the level outside the ear, without protection) and the APL (the level inside the protector).

Sound meters such as the Castle Vocis real-time octave band meter can calculate all this on-screen by using a built-in database of hearing protection data.

So what's new and what does it all mean

The Control of Noise at Work Regulations is already available in draft form and has been through a consultation process. This is where lots of industry people get to look at it and send in comments to the HSE such that the outside world can have its say before the regs are made and laid. This does mean that the items in this article are subject to change so care should be taken and the final HSE document should be read in full. The following points are the main changes from the existing Noise at Work Regulations 1989, which is to be repealed.
 
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