When noise levels are particularly high (for example, greater
than 90 dBA), it is important to assess the performance of the
hearing protection that is being used. Three methods are available
for calculating the sound level at the ear. This page covers the
Single Number Rating, or SNR method
. The other methods are Octave Band and HML.
For the SNR method you just need to measure the C-weighted sound
level of the noise in question. This sound level is entered into
the hearing protection calculator,
along with the hearing protector's SNR figure,
which should be provided by the manufacturer.
In this example the hearing protectors SNR figure is 28 and the
C weighted Sound Level is 97.0 dB(C). The resultant level at the
ear, including the 4dB real-world factor, is 73.0 dB.
Two results are shown:
Calculated Level
This is the level at the ear calculated to the
standard ISO 4869-2:1995.
Real World +4dB
In the real world there are factors that can reduce the effectiveness
of hearing protectors: imperfect fitting and the condition
of the protectors are two examples. To allow for this the HSE
recommends the addition of 4dB to the calculated level at the
ear.
Over Protection and Under Protection: You should
usually aim to reduce the noise level at the ear to between 70
and 80 dB. If you reduce it below 70 dB then there is a good chance
that you are over-protecting, making it difficult to hear speech
and warning sounders. The worker is also less likely to wear such
protection at all times.
