Frequently Asked Questions (FAQ)
1. What is noise pollution?
2. Measuring sound by decibel (dB)
3. How loud does noise have to be before it's dangerous?
4. Does the law protect me against noise?
5. Is there evidence that noise can make us sick?
What is Noise Pollution?
Noise pollution is not easily defined because it is different from other forms of pollution.
One measure of pollution is the danger it poses to health. Noise causes stress, which is a leading cause of illness and suicide. Therefore, any form of noise can be considered pollution if it causes annoyance, sleeplessness, fright, or any other stress reaction.
- Noise is transient; once the pollution stops, the environment is free of it. This is not the case for chemicals, sewage, and other pollutants introduced into the air, soil, or water.
- Other forms of pollution can be measured, and scientists can estimate how much material can be introduced into the environment before harm is done. We can measure individual sounds that may damage human hearing, but it is difficult to monitor cumulative exposure to noise or to determine just how much is too much.
- The definition of noise itself is highly subjective. To some people the roar of an engine is satisfying or thrilling; to others it is an annoyance. Loud music may be enjoyable or a torment, depending on the listener and the circumstances.
Broadly speaking, any form of unwelcome sound is noise pollution, whether it is the roar of a jet plane overhead or the sound of a barking dog a block away.
The actual loudness of a sound is only one component of the effect it has on human beings. Other factors to consider are the time and place, the duration, the source of the sound, and whether the listener has any control over it. Most people would not be bothered by the sound of a 21-gun salute on a special occasion. On the other hand, the thump-thump of a neighbour's music at 2 a.m., even if barely audible, could be a major source of stress.
Measuring Sound by Decibel (dB)
The decibel (dB) is a measure of sound intensity; that is, the magnitude of the fluctuations in air pressure caused by sound waves. The decibel scale is logarithmic, not arithmetic. This means that a doubling of sound intensity is not represented as a doubling of the decibel level. In fact, an increase of just 3 dB means twice as much sound, and an increase of 10 dB means ten times as much sound.
A sound pressure level of 0 dB represents the threshold of hearing in the most sensitive frequency range of a young, healthy ear, while the thresholds of tickling or painful sensations in the ear occur at about 120 to 130 dB.
Decibels are usually measured with a filter that emphasizes sounds in certain frequencies. The "A" filter (dBA) is the one most frequently used. The "C" filter (dBC) puts more weight on low-frequency sounds such as the bass in amplified music.
The perception of loudness by the human ear is not directly proportional to the decibel level. For example, a sound 10 dB greater than another is not perceived as being ten times as loud but only about three times as loud.
The intensity of noise diminishes with distance. Outdoors, and in absence of any close reflecting surface, the effective decibel level diminishes at a rate of 6 dB for each factor of two increase in distance. For example, a sound measuring 100 dB at 10 metres would be 94 dB at 20 metres, 88 dB at 40 metres, and so on.
How loud does noise have to be before it's dangerous?
Because permanent hearing loss is usually a long-term process, it is impossible to know at exactly what point noise becomes loud enough to cause damage to the ears.
The U.S. Environmental Protection Agency has established 70 dBA as a safe average for a 24-hour day. (This figure is based only on the risk to hearing, and does not take into account other health factors such as loss of sleep.)
Since sound intensity doubles with every increase of 3 dB, the time of safe exposure would be cut in half with each such increase. Thus a worker should wear ear protection if exposed to a steady 75 dBA for eight hours, 78 dBA for four hours, and so on. Brief exposure to noises of up to 100 dBA is not considered risky, provided the average remains within the prescribed levels.
Actual limits for labour tend to be more permissive. In most jurisdictions, workers are permitted to be exposed to up to 85 or even 90 dBA for eight hours. Using the higher of these figures, the sound level in a typical nightclub, 110 dBA, could pose a risk of permanent hearing damage after as little as four minutes of exposure.
Of course, noise is dangerous in other ways too. It can be a cause of stress, illness, suicide, aggression, and violence. As stated above, the volume of noise is only one component of its effect.
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Does the law protect me against noise?
In Canada and the United States there are no national, provincial, or state laws that give blanket protection against noise, though there are some specific regulations governing manufacturing standards, air traffic, vehicle mufflers, and so on. Criminal laws may also cover things like noisy parties.
Governments have traditionally viewed noise as a nuisance rather than an environmental problem. As a result, most regulation has been left up to municipal authorities.
Noise bylaws and ordinances vary widely from one municipality to another and do not even exist in some towns and cities. Where they exist, they may contain a general prohibition against making noise that is a nuisance to other people, or they may set out specific guidelines for the level of noise allowable at certain times of the day and for certain activities. Exceptions are generally made for activities considered legitimate or necessary, such as lawn mowing or garbage collection.
Regardless of how lax or stringent a local law may be, enforcement is difficult. Many municipalities do not have adequate resources to follow-up on complaints. Even where a municipality has an enforcement office, it may be unwilling to do more than issue warnings, since taking offenders to court is expensive. The police may also act on certain kinds of noise complaints, but generally do not assign them a high priority.
For persistent nuisances, the individual may have to seek damages through the civil courts. This can be a long, costly procedure with no certainty of success.
In short, legal protection against noise is very patchy and often inadequate.
Is there evidence that noise can make us sick?
Yes, though much of it is buried in scholarly journals. We know of only one book in print: Noise & Health, edited by Thomas H. Fay, published by The New York Academy of Medicine (1991). This book presents a critical and comprehensive review of available world literature on the effects of noise on all of the body's systems. It defines noise and its sources, documents the specific health hazards of noise on the body, and indicates needs for further research.
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