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Noise Terminology
Noise Glossary
Noise is notorious for its use of techno-babble in both the regulations and the data relating to it. The following definitions may help, (or may not...).
dB
dB stands for decibel - the unit of noise measurement. Not the most straight-forward
of measurement units. If we have a noise at a set level, say 80dB and then double the amount of noise energy the measured value would increase by 3dB. Hence, 88dB is twice as dangerous as 85dB. To a human however a 3dB change is just about noticeable - it sounds like a small fractional increase in the volume. For a noise to sound twice as loud to a human we need to increase it by 10dB.
To try and put that in a simpler way... If we start with 80dB and double the energy we get 83dB but it only sounds a little louder. If we increase it to 90dB it sounds twice as loud. Confused yet?
TWA
The Noise Regulations say that employers have to identify people exposed
to a maximum of 85dB(A) over an 8 hour reference period. This is basically
an averaging system - someone with an hour in a loud environment followed
by seven hours in a quiet one may overall have an 8hour exposure of below
85dB(A) and be exempt from the need to wear hearing protection. Don't
be too reliant on this though - there is an upper limit of 87dB(A) which
employees cannot be exposed to levels above so saying they can have 90dB(A)
for one hour then the rest of the day of 80dB(A) to compensate is naughty.
Types
In relation to sound meters its basically an indication of accuracy. Type
2 is OK but has a degree of in-built variation (or put another way, has
a wider range of error). Type 1 is the top one for noise risk assessments
and has a much smaller range of variation and gives more reliable results.
Octave Band
Noise is made up of many many frequencies from deep bass notes to very high pitch whistles. We need to measure all these as the noise to which your employees may be exposed may be louder in different parts of the range. This is important with hearing protection as some are better with low frequencies, some with high pitches, etc.
'C' and 'A' Weighting
The ear doesn't hear 'normally', which sounds a tad daft but there you
go. It hears different frequencies better than others and naturally enough
is focused around the main speech areas, in effect hearing them more loudly
than other less-important frequencies. When noise surveys are done an
'A Weighting' is used to make the noise meter mimic the way an ear hears,
ensuring the result is closely aligned to the actual noise exposure received
by a person. C Weighting is another correction system and is used in calculations
for hearing protection suitability and for the peak level reached during
a survey.
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