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Spécial “ Noise at work 2007 ”
35
Acoustique
&
Techniques n° 49
Practical noise attenuation of hearing protectors according to noise directive 2003/10/EC
did not fit well between the skin and the cushion of the
earmuff (Figure 1). With middle frequency noise in the
power plant, noise attenuation was better, and minimal
noise reductions could not be observed, although the
effect of eyeglasses could be notified in the attenuation
values (Figure 2).
Discussion
In our measurements of usual ear muffs and plugs a
noise attenuation of 10-24 dB was achieved. In practice
the noise attenuation of hearing protection was usually
less than claimed in laboratory tests. Many factors
contribute to this. First, individual
differences (morphology, beard,
hair, etc.) and skills to insert
the protector vary significantly.
Secondly, simultaneous use of
other protective devices such as
eyeglasses, respiratory devices or
helmets may reduce the attenuation
of hearing protection.
MIRE measurements are quite
sensitive to errors. The miniature
microphone can be inserted into the
ear canal insuchaway that thesound
input of the microphone is blocked,
which results in an overestimation
of the noise attenuation. This
cannot be controlled visually when
the opening of the ear canal is
blocked by the ear plug. This can
be avoided by careful installation
and on-line monitoring of the signal
before the start of recording. The
protector attenuation can also
be momentarily diminished when
the subject is talking, moving or
making facial or jaw movements
during measurement.
When measurements and evaluation
are made at the entrance of the ear
canal it is much easier to check.
Reduction of noise exposure is a
key issue in the implementation of
the noise directive. For example, in
jet engine testing (Table 1), noise
exposure over a short period of time
(5 minutes/day) is 100-107 dB,
even while using noise protection
Fig. 2 : Noise attenuation of hearing protectors and combination of
hearing protectors and protective eyeglasses against low-frequency
noise of a barking drum at a cellulose factory
Fig. 3 : Noise attenuation of hearing protectors and combination of hearing protectors
and protective eyeglasses against middle frequency power plant noise
Work
Protection
Noise exposure
LAeq, dB
Noise inside a
protector
LAeq, dB
Attenuation
dB
Metal factory
Sand blasting
Ear plug
96 inside a hood
86 at ear canal
10
Metal factory
Welding, grinding,
sawing
Ear muff
98
84
14
Metal factory
Needle scaler
Ear muff
109
85
24
Cellulose factory
Inspection tasks,
n=20
Ear plug and muff
98
80
18
Cellulose factory,
Barking drum
Inspection
Ear muff
102
88
14
Repair shop
Jet engine testing Ear plug and muff
130
100-107
23-30 special
protection
Variation
10-30
Table 1 : Examples of noise exposure inside and outside the protector from industrial noise