Noise Pollution, adverse effects of noise in
our living and working environment.
Noise is, by definition, unwanted sound. It may
interfere with speech communication,
Prevent you from enjoying leisure or relaxation,
at very high levels which may occur at work or
during certain noisy leisure activities, it may
result in hearing loss
By causing damage to the hair-cells in the
cochlea in the inner ear.
Rather than leading to significant adverse
physiological responses, however, noise is more
often a major problem in terms of quality of
human life in specific localities.
Noise Levels Sound intensities are measured in decibels
(dB). For example, the intensity at the threshold of
hearing is 0 dB, the intensity of whispering is typically
about 10 dB, and the intensity of rustling leaves reaches
almost 20 dB. Sound intensities are arranged on a
logarithmic scale, which means that an increase of 10
dB corresponds to an increase in intensity by a factor of
10. Thus, rustling leaves are about 10 times louder than
whispering. Noise pollution is assessed by measuring
not only sound intensity but also regularity, distance
from source, and pitch.
REACTIONS TO NOISE
Long-term annoyance is the most convenient and
relevant measure of the impact of noise on the
“Annoyance” tends to be used to describe the general
feeling of aggravation or vexation caused by noise
It is the end of the noise/disturbance/annoyance chain.
General long-term annoyance is the most convenient
and relevant measure of the impact of noise on the
community. It takes account of all the adverse effects
of noise such as disturbance.
Studies have been carried out to examine the
relationship between exposure to noise from specific
sources (the noise dose) and the annoyance caused (the
response). Even though there is a wide variation in the
annoyance reactions of individuals, the information can
be used to define the “average” dose-response
relationship, or the percentage of the population likely
to display a specific degree of annoyance to a defined
level of noise.
When the noise is at a sufficiently high level the
opinions may be clear-cut; the noise is the main factor
in determining annoyance.
At lower levels of noise, the general attitudes of
the community as a whole, or of individual
members of the community, towards the noise
source, may assume greater importance.
The degree of annoyance may be influenced by
length of time to which a community or an
individual has been exposed to noise,
and by the time of occurrence.
Research has shown that many factors affect
sleep quality. About 20 per cent of the
population have sleeping difficulties which are
totally unrelated to noise. Age, sex, attitudes, and
health factors override the impact of noise-
induced sleep disturbance.
Background noise levels, habituation, bedroom
location, time of night, and the character of any
intruding noise also influence sleep quality.
Bearing this in mind, it is unrealistic and often
impractical to set noise limits to ensure that
sleep will not be affected in any way.
The level of environmental noise is normally measured with a
Sound Level Meter using the A-weighted decibel scale (dB(A)).
The decibel (dB) is the scale which is used to describe the sound-
pressure level of the sound. It is the logarithm of the ratio of the
measured sound pressure (which is what the eardrum detects)
relative to a reference value, which is a very small sound pressure
which automatically acquires the value 0dB. For every ten-fold
increase in sound pressure, the sound-pressure level increases by
20dB. The term “A-weighting” means that the signal is filtered in
a way that approximates to the frequency sensitivity of the
Equivalent Continuous Noise
The level of noise originating from a source is not the only
consideration affecting its impact; duration is also important.
Sometimes the noise is intermittent (for example, aircraft or train
noise), while sometimes it is more or less continuous (such as
motorway or factory noise). So, where separate noise events are
clearly distinguishable, the important factors are the maximum
level and duration of each event and the number of events in a
given period, while continuous noise is averaged in some way
over the exposure duration. Different methods have been
devised to describe the varying temporal characteristics of
different sources, but the most widely used descriptive standard
for environmental noise is the Equivalent Continuous Noise
Level (LAeq). LAeq describes the noise (in dB(A)) in terms of
the A-weighted acoustical energy of the noise averaged over a
specific time period, and is defined as the level of continuous
noise that would have the same acoustical energy as the actual
noise over the same time period.
Equal values of LAeq for different sources do not
necessarily elicit the same community reaction. The
different characteristics of the noise, both temporal and
spectral, are factors which play an important role in
determining response, which cannot be adequately
described by a measure of the noise alone. These
differences are normally taken into account when
defining standards and in noise guidelines such as the
UK Planning Policy Guidance PPG 24.
For example, a report published by Stockholm University for the
World Health Organization in 1995 has concluded that noise
levels outside dwellings should not exceed 55dB(A) to protect
the majority of people from being seriously annoyed, and that
50dB(A) should be considered the maximum desirable. These
levels can be considered as ideal targets, but because of technical,
financial, and practical considerations, exposure levels higher
than these will remain commonplace in the developed world for
some time to come, and noise-exposure standards will be set at
higher levels, although efforts will continue to be made to reduce
International noise-emission standards
International noise-emission standards are designed to control
the noise emitted by specific machines, such as aircraft, cars, or
Environmental noise exposure
Environmental noise exposure standards and
legislation are, on the other hand, normally
devised by national or local authorities to
provide an acceptable noise environment for
their specific conditions.
Noise emission levels
depend not only on the noise emitted by particular
sources, but also the distance from the source, and the
use of noise attenuation measures such as noise barriers
or double glazing which may be required to meet
national or local noise emission standards. In order to
ensure that noise levels can be predicted to an
acceptable degree of accuracy and in a consistent
manner, most countries have published official
methods for calculating noise exposure for road traffic,
aircraft, railways, and other types of noise source.
NOISE IN THE COMMUNITY
Noise from neighbours... now causes more reported complaints
than any other source.
The main sources of noise pollution in the community are
transport sources such as aircraft taking off and landing, road
traffic, and railways; fixed industrial and commercial installations;
construction activities; and (increasingly) leisure activities.
Noise from neighbours (stereo systems, late-
night comings and goings, children, barking
dogs) now causes more reported complaints
than any other source, but quantifying the
offending noise level is often a part of this type
of problem, which is more a question of
considerate behaviour than noise limits. The
noise level is also dependent on the building’s
construction and the attenuation it provides
Road traffic noise is the most widespread noise source in developed
countries. A study carried out for the European Commission by the French
institution INRETS in 1994 has estimated that some 200 million people in the
European Union (60 per cent of the population) are exposed to levels of road
traffic noise exceeding 55dB(A), and some 132 million (39 per cent) to
60dB(A). In order to reduce exposure, noise emission limits have been
defined for all new vehicle types. The limits have been progressively lowered
over the years, so that the noise emitted by new vehicles in the mid-1990s is
some 8 to 10 dB lower than 20 years before. Most of this effort has reduced
the noise from car engines and ancillary equipment so much that tyre noise,
even on urban roads, is becoming the dominant source, and “quiet” road
surfaces are now being used for some new roads, and quieter tyre designs
being considered. However, despite these efforts, the report predicted that
traffic-noise exposure levels would increase, particularly in the quieter areas,
for the following 10 to 20 years because of the growth in the number of
Although railways are generally seen as the safest, most
economical, and most environmentally friendly of all
conventional transport systems, many countries are now
reappraising the cost of new railways in terms of environmental
impact. This has been particularly true with high-speed railways.
The latest high-speed trains have been designed to be no noisier
than the older and slower conventional trains, but careful
planning of new routes and provision of noise abatement
procedures are still needed to meet environmental standards.
However, trains create a less extensive noise burden than road
traffic, so that, overall, the noise environment may improve.
Concern about aircraft noise grew rapidly after World War II and, by the mid-
1960s, it had reached such a level that aviation authorities and manufacturers
realized that noise from the early jet engines needed to be controlled and
reduced in order to create a more acceptable environment.
The predominant source of noise from both jet and propeller-driven aircraft
is the power plant itself. The pressures from environmental lobbies have
driven authorities to establish legislation to control aircraft noise by
certification and the manufacturers have made great strides to reduce noise
from the engines themselves. Noise levels have fallen by about 20dB since the
days of the early jet aircraft, which, even though they are now larger and carry
more passengers, have become far more fuel-efficient and less noisy. Whereas
the early jet engine was dominated by the jet noise and compressor whine, the
latest high-bypass ratio engine is characterized by fan noise both to the front
and rear of the engine and the relatively low level of jet noise.
While much of the work which has resulted in lower noise emission levels
from jet aircraft was driven by the need to comply with noise certification
requirements, public concern about the noise around airports led to the
introduction of noise exposure standards or limits which are generally based
Noise exposure contours, normally computer generated, are used to give an
indication of the likely noise impact at any particular location in the vicinity of
an airport. Computer modelling can also be used to evaluate the impact of
any changes, such as modifications to arrival or departure routes, or the
replacement of older, noisier aircraft with newer, quieter ones. However, it
must always be borne in mind that noise exposure contours will never give a
precise prediction of community response.
Most manufacturing and industrial operations create noise. In
many cases this may be limited to the plant’s interior, while in
others it will affect the communities in the neighbourhood.
Although the community noise problem was formerly restricted
mainly to heavy manufacturing industry, this is not necessarily
the case today, and small manufacturing or service businesses
which create noise may be located close to residential properties.
The introduction of improved ventilation and heating systems
has resulted in the installation of powerful fans located in the
walls and roofs of buildings which can, if badly positioned, lead
to significant noise levels in the neighbourhood, especially at
Construction activities are noisy and have the potential to cause
disturbance in the surrounding communities. Some sources will
generate continuous steady levels (such as fans, extractors, or
compressors), some will be intermittent (such as sawing or
drilling), while others will be impulsive (such as piling).
Environmental noise assessments take the short-term nature of
most construction activities into account by allowing higher
levels than would normally be considered appropriate for long-
term noise exposure.
Neighbours make noise; in fact, noise from the living and social
habits of our neighbours is generating more complaints than any
other single source of noise. Sources include domestic
equipment, stereo and TV, animals and children, do-it-yourself
activities, and lawn mowers. Many of these complaints may be a
consequence of poor insulation between multi-occupier
dwellings—which could be improved at the design stage, but not
after construction. Unreasonable and antisocial behaviour causes
a great deal of noise nuisance, but it is essentially a social rather
than an engineering issue. The UK Noise and Statutory Nuisance
Act 1993 now provides powers to authorities to seize noisy
equipment such as stereo systems if the owner does not comply
with an order to reduce the noise level.
The growing sophistication of leisure activities over the past few
years has led to an increase in noise levels in recreational areas,
with an associated increased potential for nuisance to nearby
residents and other visitors. Sources include power boats, micro
light aircraft, motor cycles, motor racing, clay pigeon shooting,
pop concerts, and model aircraft flying. Codes of practice and
planning regulations are used by the activity organizers and local
authorities in order to minimize the disturbance to residents and
other non-participating users of recreational areas.
Noise from military sources is generally limited
to noise from military aircraft and from practice
firing ranges. Low-flying aircraft cause
considerable disturbance en route from air bases
to exercise areas, which are usually remote and
often recreational areas (such as the Lake
District in England); the noise is likely to startle
people as the aircraft fly at high speed and at low
altitude. Military helicopters may also exercise in
the vicinity of their bases.
Practice firing ranges are used for rifle firing,
large artillery, tanks, and sometimes by air-to-
ground missiles. Although operations may be
fairly limited, the high levels of explosive noise
cause a great deal of concern about both noise
and vibration in the surrounding communities.
Good public relations can help to minimize the
adverse impact in these communities.
A small percentage of the population appears to be highly
sensitive to certain types of low-frequency noise, which is
“sensed” rather than heard. In some instances complaints cannot
be related to any identifiable source, but on occasions they can
be traced to specific sources which may be some distance from
the complainant. Once the source is positively identified, it is
sometimes possible to reduce the offending noise quite simply.
Examples of sources which can produce this type of noise
include furnaces, burners, and fans, which might under certain
circumstances set up low-frequency resonance’s within buildings,
although these will normally be at low levels.