A Scientific Insight into Noise
Noise, an unwanted or a disturbing sound, has become a hot topic
among various social strata including laymen, scientists and legal
professionals, with the government's initiative on preparation of
regulations for the control of community noise pollution, and the recent
Supreme Court decision. Professionals from various institutions are
involved in surveying and researching on different aspects of noise and
related matters. Apart from the technical aspects, noise, is related to
education, perception and attitude of the people, thus making noise
pollution control a complex matter, an Industrial Technology Institute
There is no physical distinction between sound and noise. Sound is a
sensory perception and the complex pattern of sound waves is known as
noise, music, speech etc. In technical terms sound is a disturbance of
the mechanical energy that propagates through matter as a wave (Wikipedia).
Emission of the pressure variation can be compared to the ripples in a
pond caused by throwing a stone into the water.
A wave motion through air is initiated when an element sets the
nearest particle of air into motion. This motion gradually spreads to
adjacent air particles farther away from the source. Sound or energy
thus created due to the vibration, reaches our ear as waves transmitted
Environmental noises can be quantified by different terms, the
frequency of the sound, the overall sound pressure levels and the
variation of these levels with time. Sound pressure which is the basic
measurement of the variations of air pressure that make up sound is
described by the unit Pascal (Pa). As the range of sound pressures that
human ear can detect vary widely, the pressure levels are measured on a
logarithmic scale of Pascal, which results the commonly used unit, the
Most environmental sounds are a complex mixture of many different
frequencies. Frequency describes the number of vibrations per second in
which the sound propagates and is measured in a unit termed, Hertz (Hz).
The audible frequency range lies between 20-20,000 Hz for younger
persons with unimpaired hearing. However, our hearing system is not
equally sensitive to all frequencies. It is less sensitive to lower
frequency range (20-250 Hz) and more sensitive to the mid frequency
(1000-4000 Hz) range. Because of this unequal sensitivity of the human
ear, in measuring sound the measuring instruments are set to cutoff the
less sensitive frequency range and measure only the audible range which
is indicated in dB (A). Box 1 The human organ that perceives the sound
or noise is the ear. Though the outer ear, earflap and the tube leading
inward (auditory canal) is visible, the more delicate parts of the ear
are embedded and protected deep inside the skull. The eardrum lies at
the end of the auditory canal. Sound waves strike the eardrum and
vibrate it according to the frequency. The vibration is passed on to the
ear ossicles in the middle ear. After travelling through the middle ear
sound waves reach the inner ear where a hollow chamber or the cochlea is
situated. Inside the cochlea are the fine hair-like sensory receptors.
Sound waves at various frequencies vibrate the separate tufts of these
receptors while transmitting them to the brain through the auditory
As mentioned before the human ear can respond only to the sounds
waves within the frequency (vibration/second) range of 20 "20,000 Hz.
Usually, the frequency range of our speech is between 100 "6000 Hz.
These hearing limits vary with different animal species. Although we
use the term silence, naturally there is no absolute silence. We are
constantly surrounded by numerous background sounds and they do not
become noise until they reach a certain limit. It is axiomatic that the
noise has become a major environmental polluter around the world. While
the major noise pollution in our country occurs around commercial
locations, mobile noise-makers like lottery sellers, public address
systems, household activities and entertainment events; religious
institutions also contribute to sound pollution.
Notwithstanding this, a recent survey has identified motor vehicles
as the leading noise polluter in our country. According to the survey,
the noise is mainly emitted from engines and silencers of the vehicles,
particularly buses and lorries which have been proven to be the biggest
In recent times the automobile manufacturing industry placed more
emphasis on producing environmental friendly vehicles regardless of the
vehicle category. Sound emission of the vehicle is one of the main
aspects the manufacturers consider in producing greener vehicles.
However, in the Sri Lankan vehicle market, especially the heavy
transport vehicle sector, there is an apparent demand for vehicles with
louder noises. Some of these vehicle owners deliberately replace the
factory fitted vehicle horns with louder air horns, and also change the
silencers to enhance the vehicle noise. Internationally accepted maximum
value for a vehicle horn noise is 105 dB whereas in Sri Lanka this value
exceeds beyond 115 dB. Use of these air horns will lead to a situation
where people will tend to ignore the horns of vehicles such as cars and
motorbikes. Moreover, the sudden shock caused by air horns may even lead
to road accidents. Aggravating this situation, the deafening music in
private buses, deprives the passengers' right to travel in the bus
peacefully. National Transport Commission's recent decision of
prohibiting the use of cassette players and using radios under
controlled volume levels in buses has been hailed by many.
Acting on a request made by the National Transport Commission, the
Industrial Technology Institute surveyed the noise emanated from radios
and cassette players in inter-provincial buses in establishing the base
line values to lay foundations for the recently introduced regulations.
The main objectives of this survey was two fold; first to evaluate the
existing noise levels in the buses and the second to evaluate the noise
perception by the passengers travelling in the bus.
The irony of this situation in the buses is that the driver and the
conductor, who are responsible for introducing this noise, are
continually exposed to these noise levels, and are facing a very high
risk of hearing impairment than the passengers themselves.
In order to underpin the development of the country and to reduce the
road traffic the government has started many projects to construct
highways. Speeding vehicles on highways create tire noise, which is more
prominent than the horn and engine noises. At the outset EIA reports are
prepared taking into account all these factors. However future
projections are not included in the report since facilities for noise
simulation and modelling are scarce in the country.
Beliefs and behaviours of the general public also play a great role
in noise pollution. In Sri Lanka roadside development is uncontrollable.
Notwithstanding this, the general preference of the population is to
reside in houses as close to the main road as possible, due to the
convenience of travel and access to amenities; and exorbitant land
prices are paid for this so-called luxury. These hapless residents
however, have to contend with the traffic noise and may with long-term
exposure to the noise, end up with increased threshold noise level for
hearing. Houses abutting main roads should be so designed that noise
barriers such as blind walls are set up facing the roadside. In many
other countries there are designated residential areas located away from
the main roads and also use noise barriers along the highways to reduce
the vehicle noise pollution. However at present no guidelines are
prevalent as to the permissible levels of noise in highways, roads and
other defined localities, as the Environment Act, only specifies
Industrial noise levels.
Community activities such as public address systems engaged in
entertainment, commercial, religious and household activities are the
second major category of noise pollution and this also is the most
complex category of noise pollution. Use of public address systems for
community activities is most common in Sri Lanka. However, it must be
accepted that for those who are not participating in such activities,
this could be a severe disturbance. Thus, when using a public address
system, the time of the day, duration of usage and the area coverage
should be strictly considered.
Rather than the noise, which could be evaluated, community noise
control is always entwined with aspects like culture, community and
religion. All these are extremely sensitive issues and most legislators
are reluctant to restrict. The current Supreme Court decision is
therefore most laudable.
The Hi-Fi systems used for commercial activities such as record bars,
promotional activities, lottery sellers and reception halls constitute
yet other sources of noise pollution. Often the inside noise levels of
the reception halls go beyond 90 dB (A) whereas in public address
systems it is between 65 "80 dB (A).
Entertainment activities, especially musical shows are common method
of entertainment for the public. In a designated location, a musical
show once or twice a year could be accepted and it may not be a source
of noise pollution. But in general these shows are common in many open
spaces and are very frequent throughout the year making this an
annoyance to the people living in the neighbourhood. Further the low
frequency base noise travels a long way which cannot be heard even
though it reaches the ear. Long-term exposure to low frequency base
noise could cause permanent damages to the ear.
Radius of 100 m around places of worship is legally considered as a
silent zone. Paradoxically, these silent zones themselves become a
source of noise pollution because of improper usage of the public
address systems. However, the proper usage of the public address systems
for religious institutes and festivals when and if necessary should be
accepted. Noise from households is also now becoming a problem due to
the reducing area of land plots, and apartment housing. The noise
sources could not only be radios or cassette players but also air
conditioners and generators. Industrial noise has, to some extent,
become controlled because of the regulations stipulated in gazette
extraordinary no. 924/12 of 1996 and the awareness it created.
However due to indiscriminate granting building permits,
entrepreneurs who are mindful of their obligations and have conformed to
the environmental regulations and put up their factories in almost
abandoned areas to ensure the least disturbance to the general public,
are unfairly penalized. Although these areas are called as industrial
areas, through unscrupulous means, developers buy up land in these
areas, and set up housing schemes. Complaints are then made by the
householders about the disturbances from the factory and in most of
cases the factory management is compelled to discontinue or limit their
activities or spend more on noise reduction than envisaged earlier. This
is not very encouraging to the government's stance on having more and
more industries in rural areas.
Noise causes many types of adverse health effects. According to the
WHO, the most prevalent irreversible occupational hazard worldwide is
noise-induced hearing impairment. The main social consequence of hearing
impairment is inability to understand speech in day-to-day living
conditions. Noise interferences with speech comprehension result in
large number of personal disabilities, handicaps and behavioral changes
such as problems with concentration, fatigue, irritation, decreased
working capacity, and number of stress reactions. Tintinus (ringing in
the ears) is a result of noise exposure and this could be either
temporary or permanent.
As claimed by the WHO, various studies involving workers exposed to
occupational noise and general populations, including children, living
in noisy areas around airports, industries and noisy streets indicate
that noise may have effects on human physiological functions.
The noise has been identified as an environmental stress factor.
Acute noise exposure may lead to temporary changes such as increased
blood pressure, heart rate etc. After prolonged exposure, susceptible
individuals may develop permanent effects such as hypertension and
ischemic heart diseases.
Environmental noise is not believed to be a direct cause of mental
illness, but it is assumed that it accelerates and intensifies the
development of latent mental disorders as claimed by the WHO. Noise
affects cognitive task performance and this can happen in children too.
Among cognitive effects, reading attention, problem solving and memory
are the most strongly affected by noise.
In case of the export industries, international regulations specify
the noise levels the workers could be exposed to, and the levels that
the factories are permitted to emit, in order to avert environmental
pollution and to enhance the competence and efficiency of the workers.
Most of the export industries fulfill these requirements as the buyers
specify that the factory should adhere to international regulations. The
best example is the garment industry.
Identification or seeking solutions to noise pollution is not an easy
task. Introduction of rules and regulations to control noise pollution
is a tedious and time-consuming exercise, which elicits heated responses
from the different religious groups affected, as seen during the recent
introduction of the noise regulations. Though the guidelines, rules or
regulations of foreign origin could be taken as a guide to some extent,
they cannot be adopted without modifications into our country due to the
intertwining of religion and culture with noise pollution.
What is necessary is to educate the public on the adverse effects of
nose pollution with scientific facts. Also the expertise and facilities
for scientific research and monitoring of noise pollution in the country
have to be established. Present legal status in controlling noise
pollution is not very strong in Sri Lanka except in the case of
industrial noises. Other than the gazette extraordinary no. 924/12 of
1996 there are some regulations related to public address systems in a
very scattered manner.
In all those regulations the guidelines are not stated thus making
these regulations less effective. New rules and regulations have to be
introduced along with proper mechanisms of implementation and
enforcement. In order to do this necessary infrastructure, designated
institutions and trained personnel are needed. It is unrealistic to
expect only one institution such as the Central Environmental Authority
to monitor and take action against noise pollution matters throughout
the country. The environmental officers, public health inspectors and
police should be educated with the necessary knowledge on noise related
matters. Environmental units functioning at the police stations could be
an immediate befitting solution.
Even the industrial noise regulations are based on administrative
boundaries. To illustrate, in an urban council area the noise level
could be high as 63 dB (A) and in a Pradesheeya Sabha area this could go
down to 55 dB (A). In the same administrative area there could be
silence and noise zones, regardless of the regulations on noise in that
As the noise levels set down in the regulation are based on the
administrative divisions, even a silent spot in an urban council could
be turned into a noise spot by building a factory without any legal
barrier rendering the people who lived in the area peacefully, helpless.
Noise mapping of an area and preparation of land use maps based on noise
maps could be one way of assuaging this situation. Even in the present
legal structure provisions are made for the provincial councils to
prepare land use maps. Unfortunately none of the provincial councils has
taken steps to make use of the land use mapping. Noise modelling and
simulation is another important aspect in town planning.
The expertise and facilities in noise pollution monitoring,
simulation and modelling are now well established at the Industrial
Technology Institute (formerly the CISIR), where the services of experts
could be obtained by any interested party. This will be helpful in
reducing the problems related to noise to the general public and in
selection of the land for various projects like highways, industries,
power plants etc. Traffic noise cannot be simply eliminated by imposing
rules and regulations.
Awareness plays a greater role in controlling traffic noise
pollution. While impose of regulations could be part of a long-term
plan, as a short-term plan steps to improve road manners and discipline,
changes in driving practices, improvements to driver education, etc
should be taken through various programmes such as Horn free Week,
Driver's Week through printed and electronic media. A national policy on
noise is of utmost importance. By road noise mapping the areas affected
by the vehicle noise could be identified and could be included into the
land use map. This will be useful in identifying alternative roads,
speed limits and limitation of the heavy vehicle moving to reduce the
noise as well as the traffic. Guidelines for the noise related matters
such as levels for noise around a highway and measures that have to be
taken if that level is exceeded should be set up with the consultation
It is a prime right of the people to lead a healthy life in a calm
and quiet surrounding and providing assistance to reduce the noise
pollution is a responsibility of every right-minded citizen in the
country. More than the formal education, general knowledge, improvement
in ethics and altruism of the people of the country is what is needed.
Maximum Permissible Noise Level at Boundaries according to the Noise
Control Regulation No. 1 of 1996 Schedule I (Regulation 2) AreaLAeqT (dB(A))
Day TimeNight Time Low Noise Area (Pradeshiya Sabha Area)5545 Medium
Noise Area (MC & UC Area) 6350 High Noise Area (Industrial Area)7060
Silent Zone5045 If the local Authority applies the Noise Zone map then
the Maximum Permissible Noise Level at Boundaries Schedule IV
(Regulation 7(a)) AreaLAeqT (dB(A)) Day TimeNight Time Rural Residential
Area5545 Urban Residential Area6050 Noise Sensitive Area5045 Mixed
Residential Area6355 Commercial Areas 6555 Industrial Area7060. The
sound originates as a result of a mechanical vibration that propagates
through air by varying the air pressure on the propagation pathway and
the primary measurement of air pressure is Pascal (Pa).
The lowest sound that the human ear can perceive or the threshold of
hearing is about 20 Pa. The highest sound level that can be tolerated is
100 Pa. The ratio between these two extremes is million to 1. Measuring
noise value in Pa, thus can lead to unwieldy numbers. Conversion of the
value in Pa to its logarithmic number makes the value of the sound
measurement simpler. The logarithmic value of Pa is known as Decibel
(dB). Decibel values of several environmental noise sources are given in
the above figure. The advantage of dB is that almost all the
environmental noise sources lie between a range of 0 to 130 dB(A).
However we cannot find zero dB or absolute silence in nature. The lowest
value of noise in natural environment is about 30 dB (A).