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The main property of
sound
is its frequency: the number of vibrations per second. The frequency range the human ear can
hear as sound is 20–16000 Hz. The unit of sound pressure is decibel (dB). It indicates how many times the pressure of a given
sound exceeds the reference value of 20 µPa, the faintest sound audible for the human ear at 1000 Hz.
Hearing protection
standards set the medical threshold level at 80 db for static noise (where the oscillation of the sound
pressure stays within a range of 5dB) and 135dB for impulse noise (individual sound impulses separated by gaps of at least
10ms). In work environment with noise levels not clearly below these thresholds, the noise level must be measured and then
the necessary measures (regarding personal protection gear, technical noise reduction, modification of equipment and
workflow etc...) taken accordingly. The threshold level of noise exposure cannot exceed 87dB (L
EX
,8h) or 140 dB (L
max
), even
if protective gear is used. On top of severe and irreversible health risks, ignoring regulations and standards regarding noise
protection also has other immediate and harmful effects, like high pulse rate and blood pressure, sudden fatigue, loss of
concentration, headache, nausea or an impaired sense of balance.
When choosing the proper ear muffs (EN352-1) or earplugs (EN352-2), it is important to consider the fact that even
at the same noise level, the degree of protection these devices provide depend on the frequency of the noise.
And even the right noise attenuation device offers proper protection only if it applied and used correctly - the way it is explained
in its user manual.
Noise volume (dB) Duration of exposure without noise-induced hearing loss
80 dB
Vacuum cleaner Hearing protection gear is recommended*
85 dB
Diesel locomotive
8 hours
Hearing protection
device is compulsory
88 dB
Lawn mower
4 hours
91 dB
Electric drill
2 hours
94 dB
Printing press
1 hour
97 dB
Hewing machine
30 minutes
100 dB
Buzz saw
15 minutes
110 dB
Jackhammer
30 seconds
120 dB
Railway horn 2 seconds (pain threshold)
130 dB
Gunshot
1 second
140 dB
Fighter jet
0.5 second
* If the noise level exceeds 80dB, the employer must provide the workforce with proper protection devices, which are compulsory
for the employers to wear if the noise level exceeds 85dB. Please, note: the noise level can’t be reduced 15dB or more below the
intervention limit, as it may negatively effect communication, which in turn may have serious consequences. It is also important to
know that, due to the logarithmic nature of the way sound travels, the total amount of noise exposure with two sources of the same
noise level shows a 3dB increase: two sources with noise levels of 90dB each, for example, will have a combined noise output of 93dB.
Hearing protection gear types
Passive noise attenuation devices
– Earplugs: disposable, reusable (washable), banded.
– Passive ear muffs: with headband, with nape band, clip-on
– Electronic ear muffs: noise level dependent; capable of blocking ambient noise (e. g. harmful, impact type noise over
82dB) and/or receiving audio signals (ear muffs with built-in radio, ear muffs capable of two-way communication through
connected devices, incl. telephones, walkie-talkies, microphones or adapters).
Active noise attenuation devices: The counter-phase sound waves created by the speakers inside the muffs (acting as
secondary sound sources) create interference with, and thus cancel out the unwanted – for example low frequency – noise.
Major standards regarding hearing protection gear
EN 352-1
Ear muffs
EN 352-2
Earplugs
EN 352-3
Clip-on ear muffs
EN 352-4
Noise level dependent ear muffs
EN 352-5
Active noise attenuation ear muffs
EN 352-6
Ear muffs with electric input
Methods of determining the efficiency of hearing protection
– the octave band method: the noise attenuation efficiency of the device is measured at set frequency intervals (63/125Hz to
8,000Hz); the confirmed noise attenuation efficiency and frequency-projected protection level of the device is calculated by
subtracting the standard deviation of the measured values from the above set frequency interval efficiency values.
EARLINE
®
• HEARING PROTECTION GEAR
– The HML method: this method indicates the protection gear’s efficiency based on the average values of the device’s high (H),
mid-range (M) and low (L) frequency noise attenuation. In other words, it indicates the number of decibel’s by which the gear
reduces the noise level on the given frequency band, C- and A-weighted noise pressure levels also taken into consideration.
- Single Number Rating (SNR): A simplified noise reduction value for the simplest way of quantifying the efficiency of a hearing
protection device in a given noise exposure. The so called A-weighted noise pressure level (L
A
) inside the ear is calculated by
subtracting the SNR value from the work environment’s typical C-weighted noise pressure level (L
C
, the combined value of all the
audible noise). The protection device works properly if it reduces the noise level below the designated exposure threshold (85dB).
