By

James McCann

2

NOISE

Noise Pollution, adverse effects of noise in our living and working environment.

3

Noise is, by definition, unwanted sound. It may

be;

annoying,

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

4

Damage By causing damage to the hair-cells in the

cochlea in the inner ear.

5

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.

6

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.

7

8

Long-term annoyance is the most convenient and relevant measure of the impact of noise on the community.

“Annoyance” tends to be used to describe the general feeling of aggravation or vexation caused by noise nuisance.

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.

REACTIONS TO NOISE

9

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.

10

When the noise is at a sufficiently high level the opinions may be clear-cut; the noise is the main factor in determining annoyance.

11

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.

12

The degree of annoyance may be influenced by

the;

length of time to which a community or an

individual has been exposed to noise,

and by the time of occurrence.

13

Sleep Disturbance

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.

14

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.

15

DESCRIBING NOISE

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 human ear.

16

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.

Equivalent Continuous Noise

Level (LAeq).

17

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.

18

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 them.

19

International noise-emission standards are designed to control the noise emitted by specific machines, such as aircraft, cars, or industrial equipment.

International noise-emission standards

20

Environmental noise exposure

standards

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.

21

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.

22

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 IN THE COMMUNITY

23

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 between dwellings.

24

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 vehicles.

Road Traffic

25

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.

Railways

26

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.

Aircraft

27

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 on LAeq.

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.

28

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 night.

Industry

29

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.

Construction

30

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.

Social Noise

31

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.

32

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.

Military Sources

33

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.

34

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.

Low-Frequency Sources