is defined as unwanted sound that lacks a musical quality. Noise pollution is defined as annoying or damaging environmental noise levels that come from sources such as automobile engines, industrial machinery, or amplified music.
Attempts to control environmental noise levels were noted as early as 509 B.C., when Roman chariots were banned from racing on streets at night due to the excessive sounds of clattering wheels and horses' hooves.
The concept that noise might be harmful to one's health has been recognized and recorded for several hundred years. In 1713, Bernardo Ramazzini in Venice wrote about the health of workers in different occupations. He noted that coppersmiths tended to work in specific areas of the city; the perpetual hammering in these zones led to hearing difficulties and eventual deafness in the workers, as well as in their immediate neighbors.
The Industrial Revolution of the late 1700s and early 1800s brought the rise of machinery whose noise levels were not regulated. The newly-invented steam engine and the internal combustion engine contributed to the environmental noise.
City dwellers and workers in the late 1800s were subjected to escalating amounts of environmental noise, due to population increases and poor city planning that placed industrial and residential areas in close proximity. In response, the U.S. Congress passed its first noise-related bill in 1907, placing controls on the use of steamboat whistles.
The subject of noise was first considered as a public health issue in 1912 with its inclusion at the 15th International Congress on Hygiene and Demography. These congresses were held in various European capitals every 2-3 years to discuss issues and statistics relating to public health and disease prevention. The first congress took place in 1877 in Brussels; the final meeting occurred in Washington, D.C., in 1912.
The science of noise measurement began in the 1920s when the Bell Telephone Company created the bel as a unit of measure for the strength of audio signals along its telephone lines. The much smaller logarithmic unit of a decibel (dB), one-tenth of a bel, has since taken the bel's place as the common measure of a sound's loudness and intensity.
The first scientific survey of city-related noise levels was conducted in New York City in 1926 by Dr. E.E. Free, the science editor of Forum Magazine. This survey created "noise maps" of the city showing where (and how much) noise emanated from cars, street cars, and industrial companies.
Public health research on noise and noise abatement stalled in the late 1930s; at that time, municipal health authorities turned their focus to more immediate public health issues such as measles, syphilis, tuberculosis, and dental health.
In 1965, the National Research Council Committee on Hearing, Bioacoustics and Biomechanics (CHABA), along with the National Academy of Science, set criteria for safe noise exposure levels. These criteria were based on the outdated concept of damage risk: how much hearing loss was acceptable following a lifetime of noise exposure. CHABA stated that noise exposure would be "deemed acceptable if, after 10 years of near-daily exposure, the resulting median hearing loss did not exceed 10dB at frequencies less than or equal to1kHz, 15dB at 2kHz, and/or 20dB at frequencies greater than or equal to 3kHz."
According to federal documentation, the Noise Control Act of 1972 established a national policy in the United States to promote an environment free from noise that jeopardizes people's health and welfare. The Act established a means for the coordination of federal research and activities in noise control; it also authorized the establishment of federal noise emissions standards for products distributed in commerce, and provided information to the public in respect to the noise emission and noise reduction characteristics of those products.
According to the Noise Control Act, hearing loss can be prevented by maintaining average noise exposure levels of 70dB or less over a period of 24 hours.
Outdoor sounds with levels of 55dB, and indoor sounds with levels of 45dB, may help to prevent "annoyance" and interference with a person's activities. These lower levels allow for normal conversation, sleep, and recreation.
The Hearing Conservation Amendment of 1983 set a permissible level of 90dBA for eight hours of continuous sound in the workplace. dBA is a "weighted" decibel measurement, where the decibel levels of low-frequency sounds are reduced in comparison to those of higher-frequency sounds; low-frequency sounds (below 1000Hz) are difficult for the human ear to distinguish.
Many government groups and non-profit organizations promote awareness of noise pollution; they also support the creation of noise abatement policies and procedures.
Notable noise reduction advocacy groups include: Acoustical Society of America (ASA), European Acoustics Association (EAA), U.S. Environmental Protection Agency (EPA) Office of Noise Abatement, Federal Aviation Administration (FAA), International Commission on Biological Effects of Noise (ICBEN), National Hearing Conservation Association (NHCA), National Institute for Occupational Safety and Health (NIOSH), National Transportation Safety Board (NTSB), Noise Abatement Society, and the Noise Pollution Clearinghouse (NPC).
As people age, hearing generally declines from exposure to everyday sounds. Experts believe that long-term exposure to loud noises is one of the main causes of permanent hearing loss in adults. For instance, construction workers who are regularly exposed to loud equipment and do not wear protective gear have an increased risk of developing irreversible hearing loss.
According to the European Action on Noise Pollution Health Effects Reduction program (NOPHER), over 500 million people worldwide are exposed to dangerously high noise levels; 30 million of these affected people are in Europe. Another 80 million people face daily environmental noise levels that exceed 65dB, a level that may cause sleep disturbance and annoyance.
Based on information supplied by NOPHER, noise-related hearing loss affects the economic output of countries. The lowest estimated effect on European GDP in 1999 due to lost productivity was 0.2%, or about 12 billion Euros per year ($15.6 billion USD).
Ten percent of collective-bargaining contracts that expired in the United States in 2007 included clauses concerning the prevention of workplace noise and the protection of workers exposed to high levels of noise as part of their employment. Six percent of those agreements provided for noise abatement programs that included noise-level reviews of new equipment. Top industries affected by the collective-bargaining agreements included: metal (affecting 17,000 workers), electronic machinery (22,000 workers), and transportation equipment (346,000 workers).
About 10 million Americans have hearing loss that may have resulted from occupational and/or recreational exposure to noise without the use of sufficient hearing protection. Recreational sources of noise include amplified or portable music systems, vehicles (such as motorcycles and ATVs), and the use of firearms or power tools.
The Bell Telephone Company pioneered the science of noise measurement in the 1920s, with its creation of the bel as a unit of measure for the strength of audio signals along its telephone lines. The smaller decibel measure (one-tenth of a bel) eventually replaced the bel as the common gauge of a sound's loudness and intensity.
The decibel scale begins at the level of zero, which is almost total silence. Each numbered jump of 10 in dB level corresponds to a sound that is 10 times louder than the previous level. For example, a 10dB level (equivalent to the sound of normal breathing) is 10 times more powerful than 0dB. A 20dB noise (such as a loud whisper), is 100 times more powerful. Samples of additional dB ratings include a normal conversation (60dB), a vacuum cleaner (70dB), a garbage disposal (80dB), and an airplane taking off (120dB). Continuous exposure to sounds above 85dB can result in hearing loss; people in an 85dB environment need to raise their voices in order to be heard.
There are three basic devices for measuring sound in the workplace: A handheld sound level meter (SLM), which measures noise levels at a specific point in time; a portable dosimeter, which attaches to a worker's clothing and averages the sound levels experienced by the worker while moving through the workplace over a period of time; and an integrating sound level meter (ISLM), which is a handheld device that measures noise levels in one specific location over specified time period.
Sound level meters also measure outdoor environmental noise levels related to cars, buses, motorcycles, airplanes, and trains, as well as noise that leeches from industrial areas into residential neighborhoods. Outdoor meters vary in their size, weather durability, and available features (such as the ability to filter sounds within certain frequencies and to monitor noise levels at timed intervals).
When people are exposed to harmful noise, or sounds that are too loud or loud sounds that last a long time, sensitive structures in the inner ear may be damaged. These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, these sensitive hair cells cannot grow back, and permanent hearing loss may result.
General: Noise pollution is both a public health and an environmental stressor that may result in wide-ranging physical and psychological deficits.
The European Action on Noise Pollution Health Effects Reduction program (NOPHER) was established in 1999 to improve the effectiveness and quality of European research on noise pollution and its impact on health. It created scientific workgroups in six research areas: the effects of transportation noise on health; new ways to protect hearing; the harmful effects of industrial chemicals on hearing; the effects of noise on children; the creation of testing to predict noise-induced hearing loss; and a computerized environmental noise health data collection and education system on the subject of hearing conservation. NOPHER launched an international journal on Noise and Health to aggregate research results on the subject in one publication. Due to media coverage of NOPHER's meetings, the organization has contributed to a world-wide increase in awareness of noise pollution and its health effects.
According to Rabinowitz, noise-induced hearing loss is a sensorineural hearing deficit that begins at the higher frequencies of 3,000 to 6,000Hz and develops gradually as a result of chronic exposure to excessive sound levels. Sensorineural hearing loss is defined as a condition where sound reaches the inner ear, but a person is not able to process the sound correctly.
Sounds are perceived as pressure or force on the hair cells that line the inner ear. When sound pressure is high (i.e., there is excessive noise), it may lead to damaged hair cells and a decrease in sound perception. The resultant loss in the perception of high-frequency sounds may cause difficulties in distinguishing consonant sounds because the spoken consonants in words tend to be higher-pitched than vowels; some high-pitched sounds may not be audible at all. Tinnitus (ringing in the ears) may also result from over-exposure to noise.
A British longitudinal study carried out over a period of 38 years found that work-related noise experienced at the age of 23 had more of an effect on hearing abilities at age 45 than any exposure to noise at the ages of 33 and 42.
Noise abatement systems: Noise abatement systems allow for the reduction of noise transmission in three main areas: construction, occupational exposure, and transportation. Noise control features can reduce ambient noise levels, but not totally remove environmental noise pollution.
Architectural solutions for noise reduction concentrate on the thickness of window glass; the quality of roofing materials; caulking standards; the construction of doors; and the assembly of walls and ceilings to meet sound transmission class standards by adding fiberglass insulation and doubling up drywall panels while increasing air space between them.
Reducing noise exposure at work is dependent on the dB level of industrial machinery in use; the dB levels of other types of office equipment and the availability of sound insulation for that equipment; the use of public address systems and alarms; and the availability of ear protection equipment. In some cases, it's possible to re-design equipment, or insulate around it, to reduce noise exposure on the job.
Transportation noise abatement primarily involves the use of noise barriers along roadways and noise reduction procedures at airports.
Noise barriers along roadways can sometimes reduce traffic noise levels by 10dB. The choice of road surface may also make a difference in perceived noise levels. The surface may be porous with small stones (quieter) or grooved with larger stones (noisier).
Aircraft noise is difficult to mitigate due to the inherent loudness of jet engine turbines. As a result, most efforts at noise reduction at airports centers around changes in flight paths; flight restrictions based on the time of day; and the soundproofing of homes in the airport's immediate area.
Health effects of noise exposure
General: According to the World Health Organization (WHO), the top health issues created by noise are: pain and hearing fatigue (e.g., when headphone users believe that headphone volume has dropped over time, even when the volume has remained the same); hearing impairment, including tinnitus (ringing in the ears); annoyance; behavioral problems such as aggressiveness; interference with conversation; sleep disturbance; cardiovascular problems; immune system disturbances caused by the stress hormones; and a decrease in work- and school-related performance.
At the 2008 International Commission on Biological Effects of Noise (ICBEN) Conference on Noise as a Public Health Problem, hearing loss in adults aged 18-59 was noted as the seventh-top disease-related affliction around the world; an estimated 20% of that worldwide hearing loss is directly due to noise. Sliwinska-Kowalska proposed a higher 30% figure of noise-related hearing loss.
According to the Noise Control Act of 1972, hearing loss may be prevented in humans by maintaining average noise exposure levels of 70 decibels (dB) or less over a period of 24 hours. Outdoor sounds with levels of 55dB, and indoor sounds with levels of 45dB, may help to prevent "annoyance" and interference with a person's activities. These lower levels allow for normal conversation, sleep, and recreation. Samples of dB ratings include a normal conversation (60dB), a vacuum cleaner (70dB), a garbage disposal (80dB), and an airplane taking off (120dB). Sounds above 85dB can result in hearing loss; people who are in an 85dB environment need to raise their voices in order to be heard. Noise levels at 120dB and higher typically result in ear pain.
According to an article in the British Medical Bulletin,
noise exposure may create additional health problems that are unrelated to hearing. These problems include: increased blood pressure and heart rate through the constriction of blood vessels; an increased risk for coronary heart disease; increased levels of adrenaline and noradrenaline (responsible for the "fight or flight" response) when exposed to high-intensity occupational noise; and changes in total cholesterol, total triglycerides, blood viscosity, platelet counts, and glucose levels.
According to a study published in the American Journal of Public Health, high noise levels related to hospital construction significantly lengthened the hospital stays of cataract surgery patients compared to cataract patients in the same hospital a year later, who were not subjected to heavy equipment noise.
According to a field study reported in 1975, helping behavior may be altered by ambient noise exposure levels. People exposed to the sound of an un-muffled 87dB lawn mower were less likely to help retrieve a pile of books dropped by a passerby than people exposed to a lesser background noise of 50dB.
Occupational and recreational noise exposure: According to British and Swedish studies conducted on workers in schools and factories, exposure to high noise levels may lead to nausea, headaches, mood changes, and a rise in anxiety levels.
About10 million Americans have hearing loss that may have resulted from occupational and/or recreational exposure to noise without the use of sufficient hearing protection. "Recreational" sources of noise include amplified or portable music systems, vehicles such as motorcycles and ATVs, and the use of firearms or power tools.
Audiology experts agree that hearing loss is increasing in the United States. Some researchers attribute these statistics to the growing popularity of MP3 players. Studies have shown that people who regularly listen to headphones, particularly earbud headphones, have an increased risk of developing hearing damage than those who do not.
Effects of noise exposure on children: Children are not immune to the effects of noise exposure on health. Bockelbrink's 2008 study of 12-year-old children with and without asthma found that asthma in girls was associated with high total levels of annoyance with noise at night or with noise around the home. There was no corresponding association between noise and asthma in boys.
According to a series of studies conducted from the 1970s through the 1990s, children exposed to noise in school might have more concentration problems than children in quieter schools. They could also display poorer reading ability; lower scores on national standardized tests; reading comprehension capabilities that are 3-4 months behind those of less-exposed children; and deficits in long-term memory. Some of these effects might, however, be reversible over time after noise exposure is withdrawn.
Effects of noise exposure on sleep: Several studies on nighttime noise exposure during sleep show that it may lead to increases in blood pressure, heart rate, and body movements. After a night of disturbed sleep, there are additional effects: a less-positive mood, a decrease in reaction times, and a perception of poor sleep quality. Some research suggests that people may be able to partially adapt to noise-related sleep disturbances, but that changes in heart rate do not adapt to nighttime noise, regardless of the number of exposures.
The 2008 ICBEN conference presented a variety of sleep-related research results. It found that: the noise level that causes awakening at night is comparable to the daytime threshold for complaining about ambient noise; there is a similar ability to fall asleep whether listening to road traffic noise or rail traffic, but people wake up more often from train noise than road noise; and people attempting to sleep are more annoyed by aircraft noise than by train or road noise.
Noise exposure combined with chemical exposure: When chemical exposure is combined with noise exposure, it may create higher risks to hearing. According to the European Action on Noise Pollution Health Effects Reduction (NOPHER), the risk of hearing loss increases from four times with noise exposure only, to 11 times when noise is combined with exposure to chemicals commonly used in manufacturing, such as toluene, lead, and mercury.
Exposure to styrene (a liquid chemical used in the creation of a wide variety of products, from CD jewel cases to food packaging and insulation) was long considered harmless at the levels used in manufacturing. A recent study, however, demonstrated a multi-factor association between amounts of styrene exposure, environmental noise levels, and hearing impairment in Finland, Poland, and Sweden.
In a study of 788 work-related fatalities between 1990 and 2005, noise was considered to be a factor in 8.5% of these deaths and was believed to be the primary issue leading to death in 2.3% of the cases. The majority of deaths were caused by moving vehicles, where warning signals could not be heard over high background noise levels.
General: Hearing protectors are needed whenever a person's hearing is exposed to noise levels that exceed a certain level and time. In the workplace, scientists have set this level at 85dB for exposures longer than eight continuous hours. The permissible exposure time is cut in half for every 3dB increase in noise level. For example, at 88dB, hearing protectors are required after four continuous hours of exposure. At 91dB, hearing protectors are required after just two continuous hours of exposure. When noise reaches 104 decibels, hearing protectors are required for exposures of less than four minutes.
Hearing protectors work by reducing the level of sound that reaches hair cells in the inner ear. Hearing protectors don't block out all noise, but they do make those noises softer.
Different hearing protectors offer different levels of protection, as shown by their Noise Reduction Rating (NRR). The higher the NRR, the greater the protection that's offered. If a hearing protector has an NRR of 22, it will reduce a potentially harmful noise by 22dB. So a 100dB noise (the decibel level of a motorcycle) will be reduced to a safe level of 78dB (100 - 22 = 78).
Hearing protectors include:
Earmuffs: These hearing protectors look like wireless headphones. The part that fits over the ear is often filled with fluid, foam, or both to ensure that the earmuffs fit comfortably and closely.
Earplugs: Earplugs are soft foam or harder plastic inserts that fit directly into the ear canal. Earplugs are cheaper than earmuffs, and come in both disposable and reusable types.
Expandable foam earplugs are designed to be rolled into a thin cylinder that is inserted about halfway into the ear canal. Once inserted, the earplug reshapes itself to fill the canal snugly.
Pre-molded earplugs are made from plastic, rubber, or silicone. These plugs have a tapered shape, similar to an ice cream cone. If washed between uses and cared for properly, pre-molded earplugs can be used repeatedly.
FUTURE RESEARCH OR APPLICATIONS
The long-term effect of "leisure" noise exposure on children needs clarification. "Leisure" noise includes exposure to high-volume music on MP3 players with headphones, as well as attendance at concerts and other venues with high ambient noise levels.
Research on the effects of environmental noise on people using hearing aids and cochlear implants is warranted.
More research is needed on the effects on multiple environmental stressors (such as air pollution and chemical exposure) on hearing loss.
The effect of noise pollution on "vulnerable" populations deserves further study. Vulnerable groups include the very young and the very old, shift workers, and patients with sleep disorders.
Further research is needed on increases in workplace accidents and fatalities due to noise-related communication breakdowns.
The economics of noise pollution requires additional study, regarding the costs of noise exposure to contemporary society.
The creation of noise policies and regulations is important to the health and growth of developing countries.
People are encouraged to take steps to protect themselves from the dangers of noise pollution. Heightened awareness should encourage individuals to turn down the volume of music, to remove themselves from noisy environments, and to wear protective gear while in noisy areas (including workplaces).
This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).
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