Sound insulation values for hearing protection

HEARING PROTECTION REGULATIONS

The level of noise at which hearing protection must be worn is determined by the daily or weekly noise exposure level and peak sound pressure level in the workplace.

• An employer must provide hearing protection at a daily or weekly noise exposure level of 80 dB(A) or a peak sound pressure level of 135 dB(C).
• Hearing protection must be worn if the daily or weekly noise exposure level exceeds 85 dB(A) or the peak sound pressure level exceeds 137 dB(C).

CHOOSING THE RIGHT HEARING PROTECTION

As its primary function, the appropriate personal protective equipment must ensure that the sound pressure level at the user’s ear does not exceed the thresholds stated above.

Since incorrect use can reduce the actual level of protection achieved, the insulation values of your chosen products should be somewhat higher than what is strictly needed. However, they should not be too high, since overprotection can prevent an employee from being sufficiently able to communicate or recognise signals. In the UK the HSE suggest that 4dB should be deducted from the protection level predicted by the product manufacturer.

SNR values and HML (high-medium-low) values are two of the tools used to assist in the selection of noise insulation products.

Factors such as comfort, ease of use and personal preference must also be taken into account during the selection process.

SNR VALUES

The SNR value (Single Number Rating) provides information about the protective effect of hearing protection products. It is an average insulation value which is calculated from all relevant frequencies. For example, earmuffs or earplugs with an SNR of 35 will reduce the noise level to which the wearer is exposed from 100 dB to 65 dB.

HML VALUES

The HML values describe the protective effect offered by hearing protection products in the three different frequency ranges: H (high), M (medium) and L (low). The selection of hearing protection using the HML method is therefore more precise than using the SNR value.

THE DECIBEL SCALE

The decibel scale is a logarithmic scale. This means it can be difficult to estimate values correctly. For example, 95 dB is perceived as being twice as loud as 85 dB. However there is a tenfold increase in sound pressure at this range.