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DateLine Sunday, 30 December 2007

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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 release said.

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 through air.

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 decibel (dB).

Hearing system

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 nerve.

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 noise makers.

Air horns

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.

Sensitive issues

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.

Sources

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.

Modifications

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 administrative district.

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 of experts.

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).

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