SV 104A USER'S MANUAL_______________________________________________________
11
1.1
Sound pressure
The human ear responds to audible sound pressure levels in the
range from 20 μPa (hearing
threshold) to 20 Pa (pain threshold), resulting in the enormous scale 1:10,000,000. Since using such a large
arithmetic scale is not practical, a logarithmic scale in decibels (dB) was introduced which is also in agreement
with physiological and psychological hearing sensations. Therefore, it is common that sound pressure is
measured in decibels. Below there is sample information about expected sound levels for different sources.
Sound source
Sound level [dB]
Jet aircraft, 50 m away,
or gunshot at close range
140
Threshold of pain
130
Threshold of discomfort
120
Chainsaw, 1 m distance
110
Disco, 1 m from speaker
100
Vacuum cleaner, distance 1 m
70
Conversational speech, 1 m
60
Quiet library
40
Rustling leaves
10
Hearing threshold
0
Table 1-1
Example sound source levels
1.2
Dosimetry
Noise is definitely a serious hazard in many workplaces. In case exposure to noise from machinery
processes and equipment is not correctly eliminated or controlled, it may cause permanent hearing loss
in workers. The, so called, inner ear is very fragile part of our hearing sense, which with current knowledge
in medicine, cannot be truly repaired. Therefore, it is of great importance to protect our senses from excessive
noise. Exposure to high levels of noise may also create physical and psychological stress, reduce productivity
and interfere with normal communications. This may lead to accidents and injuries by making it difficult to hear
moving equipment, other workers, and warning signals. Undoubtedly hearing loss has a very significant impact
on the quality of life for many workers and their families.
Therefore, measuring noise exposure in the workplace is fundamental part of all good hearing
conservation and noise reduction programs. The aim of taking a measurement with a noise dosimeter is to
evaluate the average exposure of employees to noise during a normal shift. Wherever the worker goes the
noise dosimeter goes too so that it captures all of the harmful noise during the typical day.
The dosimeter may be worn for the complete shift if the work pattern is so variable that it is difficult to
predict exactly what will occur or it may be worn for a shorter but representative pe
riod and then the full day’s
dose extrapolated from that sample.
1.3
Standards
The effects of high sound exposure on hearing have been studied for many years. As far back in 1954
AIHA (American Industrial Hygiene Association)
– Rosenwinkel & Stewart – described a “new device which
integrates sound energy over finite time periods.
” In 1956 – von Witternand & von Gierke obtained a patent for
a
noise exposure meter for “indicating the total time that noise exceeded a certain predetermined levels.”
Since then, measurements could be conducted over long periods of time and the instrument was worn by
personnel under normal work conditions.
Finally, organizations developed standards to regulate personal noise exposure. International standards
are specified by health and safety regulations such as the European Union Parliament and Council Directive
2003/10/EC of February 6, 2003 on minimum health and safety requirements regarding the exposure of
workers to the risks arising from physical agents (noise) or International Electrotechnical Commission IEC-
61252 guidelines. The EU directive links to the ISO 9612-2009 Acoustics
– Determination of occupational
noise exposure
– Engineering method.
