When noise levels are particularly high (for example, greater
than 90 dBA), it is important to assess the performance of the
hearing protectors that are being used. Three methods are available
for calculating the sound level at the ear. This page covers the
more accurate Octave Band Method. The other methods
are HML and SNR.
You also need the Assumed Protection Values or
APV for each hearing protector. This is the expected
attenuation that the protector offers in each of the octave bands.
If the APV is not provided then it is equal to the Mean
Attenuation - Standard Deviation in each band.
In the example above, the hearing protector's APV values have
been entered along with the sound level measured in each octave
band. The results are shown along with a summary that indicates
these protectors as being Inadequate as the level
is still too high.
The following 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.
Graph
The graph shows the measured noise level in red and the calculated
level at the ear in green. This simple graph can by handy for
spotting tonal problems.
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.
