Noise is defined as an unwanted sound or a combination of sounds that has adverse effects on health. These effects may be in the form of psychological damage or actual harm to the body itself. Noise may be subjective in that a sound or combination of sounds may not be annoying to one person but may be for another person, thereby resulting in psychological or bodily adverse effects. However, loud sounds are generally accepted as noise to all individuals as they have been demonstrated to cause ill effects to hearing.
The unit of sound intensity is known as a decibel. Examples of typical sound intensities are as below:
The following is a list of decibel intensities taken from Encarta 2005.
dB - Activity
0 - Threshold of hearing
10 - rustle of leaves, a quiet whisper
20 - average whisper
20 to 50 - quiet conversation
40 to 45 - hotel, theater between performances
50 to 65 - loud conversation
65 to 70 - traffic on a busy street
65 to 90 - train
75 to 80 - factory noise( light/medium work)
90 - heavy traffic
90 to 100 - thunder
110 to 140 - jet aircraft at takeoff
130 - threshold of pain
140 to 190 - space rocket on takeoff
Simply measuring the physical intensity of the stimulus as a sound pressure level cannot assess the potentially damaging effect of noise. The human ear does not respond equally to all frequencies—high frequencies are much more damaging than low frequencies at the same physical intensity levels.
Consequently, most sound level meters are equipped with a filter that is designed to de-emphasize the physical contribution from frequencies to which the human ear is less sensitive. This filter is referred to as the A filter, and measurements taken using the A filter are reported as dBA. This is known as the A level on a sound pressure meter.
Noise is defined as an unwanted sound or a combination of sounds that has adverse effects on health. It can impact a person’s health when the intensity of the noise or the duration of the noise are excessive. Chronic exposure to loud noises results in a typical type of hearing loss known as Noise Induced Hearing Loss, which typically affects the higher frequencies. It may also result in the presence of Tinnitus (ringing sound in the ear). These are due to harmful effects of the loud sounds on the hearing organ (cochlea) over time.
The psychological effects of noise are usually not well characterized and often ignored. However, their effect can be equally devastating and may include hypertension (high blood pressure), tachycardia (fast heartbeat), increased cortisol (stress hormone) release and increased physiologic stress. Collectively, these effects can have severe adverse consequences on daily living and globally on economic production.
Studies have made the following associations with exposure to noise. Exposure to noise, especially on a prolonged basis may result in a higher incidence of high blood pressure (hypertension). Children living in a noisy community had a poorer quality of life compared to those in a quiet community.
Children in noisy environments also have decreased attention on tasks and have lower performance on cognitive assignments compared to children in quiet environments. Furthermore, noise (traffic noise in this study) can significantly impair the reading ability and comprehension as well as basic mathematical performance in children.
Noise can also cause many deleterious effects on sleep. It can cause frequent early morning awakenings8. The time taken to fall asleep can increase up to 20 min with peak noise levels of 45dB9.
Chronic noise exposure also increases fatigue symptoms and postwork irritability and makes relaxing and being able to unwind extremely difficult.
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Evans, G.; Bullinger, M.; Hygge, S. Chronic noise exposure and physiological response: A prospective study of children living under environmental stress. Psychol. Sci. 1998, 9, 75-77.
Cohen, S.; Evans, G.; Krantz, D.; Stokolos, D. Physiological, motivational, and cognitive effects of aircraft noise on children: Moving from the laboratory to the field. Am. Psychol. 1980, 35, 231-243.
Cohen,S.;Krantz,D.;Evans,G.;Stokolos,D.;Kelly,S.Aircraftnoiseandchildren:Longitudinal and cross-sectional evidence on adaptation to noise and the effectiveness of noise abatement. J. Personality Soc. Psychol. 1981, 40, 331-345.
Hygge, S.; Boman, E.; Enmarker, I. The effects of road traffic noise and meaningful irrelevant speech on different memory systems. Scand. J. Psychol. 2003, 44, 13-21.
Shield,B.;Dockrell,J.The effects of noise on children at school: A review. Build. Acoust.2003, 10, 97-116.
Ljung,R.;Sorqvist,P.;Hygge,S.Effectsofroadtrafficnoiseandirrelevantspeechonchildren's reading and mathematical performance. Noise Health 2009, 11, 194-198.
Muzet, A. Environmental noise, sleep and health. Sleep Med. Rev. 2007, 11, 135-142.
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Melamed S, Rabinowitz S, Green MS. Noise exposure, noise annoyance, use of hearing protection devices and distress among blue-collar workers. Scand J Work Environ Health. Aug 1994;20(4):294-300.
Noise induced hearing loss (NIHL) is generally defined as hearing loss that develops slowly over a long period of time (several years) as the result of exposure to continuous or intermittent loud noise. Continuous exposure to sounds greater than 85 dB for 8 hours has been shown to cause NIHL.
This typically affects the high frequency hearing rather than the low frequency hearing. The cells in the hearing organ (coclea) are permanently damaged with such chronic exposure to loud noise. Noise Induced Hearing Loss takes years to develop, usually 10 years or more to develop significant hearing loss.
When hearing loss is limited to the high frequencies, individuals are unlikely to have difficulty in quiet conversational situations. The first difficulty the patient usually notices is trouble understanding speech when a high level of ambient background noise is present. As NIHL progresses, individuals may have difficulty understanding high-pitched voices (eg, women's, children's) even in quiet conversational situations. Conversation on the telephone is generally unimpaired because telephones do not use frequencies above 3000 Hz.
Exposure to loud noise over short durations of a few hours may also cause temporary hearing loss, a condition called a Temporary Threshold Shift (TTS). It may also cause temporary tinnitus (ringing sound in the ear).
Finally there is hearing loss due to Acoustic Trauma. Acoustic trauma is due to one-time brief exposures followed by immediate permanent hearing loss. The sound stimuli generally exceed 140 dB and are often sustained for less than 0.2 seconds. Such loud sounds over such a brief period (called impulse noises) cause damage to the ear drum, small bones of the ear that are used for hearing and also directly damages the cells of the hearing organ (cochlea) itself. Examples of impulse noise include explosions and gunfire.
Recent studies suggest that some people are genetically predisposed to hearing loss due to Noise exposure. Obviously those who are in occupations which expose them to loud noises on a regular basis will be susceptible to Noise Induced Hearing Loss. Occupational noise accounts of 16% of the disabling hearing loss in adults worldwide resulting in decreased economic production.
A few local studies performed in Singapore highlights the prevalence and severity of the problem of Noise and Noise Induced Hearing Loss. A study of employees in local discotheques revealed that they were all exposed to loud noise (at least 89dBA Leq) for their whole shift and had a statistically significant higher prevalence (41.9%) of hearing loss compared to the control (normal) group (13.5%). 21% of the employees also had tinnitus ( ringing sound in the ear) compared to only 2.7% in the control group.
In another study of our young Singaporean men enlisting for National Service, they found that the relative risk of hearing loss is higher in subjects with frequent discotheque visits compared to those who never do so.
Another study showed that Noise Induced Deafness or Hearing Loss is the leading occupational disease in Singapore with 500 new cases of Noise Induced Deafness (NID) detected by the Department of Industrial Health (DIH) every year. The main jobs at risk were grit blasters, steel workers, fitters, boiler fabricators, panel beaters and carpenters.
Another local study showed that there was a prevalence of 23.3% of tinnitus (ringing sound in the ear) amongst workers exposed to noise.
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Hearing protection and monitoring is vital to prevent Noise Induced Hearing Loss. This can be instituted on a systemic level at the workplace, as well as at the individual level.
Every noisy workplace should set up an in-plant Hearing Conservation Programme (HCP) which includes periodic audiometric examination of workers. In Singapore, since 1985, workers in many noisy workplaces are required to undergo statutory pre-employment and annual audiometric examinations arranged by their employers. The examinations are carried out by Designated Factory Doctors who have undergone a course of training in occupational health and are registered with the Labour Ministry.
The doctors' role includes advising workers and employers on the prevention of noise-induced deafness (NID). Doctors notify cases of NID to the Ministry of Labour which conducts investigations where indicated. Since NID is insidious, workers with the condition would not be detected in the early stages without an audiometric examination.
With the introduction of the statutory examinations, more noise-exposed workers were examined and cases of early hearing impairment picked up. The statutory medical examinations have helped to highlight the problem of the noise hazard. Individual companies are able to monitor the noise problem in their workplaces, using the audiometric results to supplement the noise assessments. Susceptible workers can be identified and followed up more closely, and health education intensified.
Hearing conservation programs will be necessary if noise exposures in the workplace exceed 85 dBA. The following are some measures employed:
- Noise levels must be posted in work areas
- Baseline audiometry (hearing test) and regular audiometry (yearly)
- Training on the effects of noise and the purpose of audiometric testing and the use of hearing protective devices
If exposure to loud environmental noises cannot be avoided, hearing protection should be used. Unfortunately, enforcement has been sporadic. HPDs vary considerably in their effectiveness, comfort, and cost. The following information should be taken into consideration when considering HPDs:
Only devices that are designed for hearing protection and tested for efficacy should be used. Items such as cotton, tissue paper, and expended cartridge casings provide no meaningful noise attenuation.
Earplugs are available with attenuation levels from as low as 10 dB to as high as 32 dB. They can be purchased over the counter or custom made. Earplugs can be as effective as earmuffs. However, earplugs are effective only when properly inserted. When earplugs are improperly inserted, noise attenuation may be eliminated or greatly reduced. Earplugs are especially useful when noise exposure is continuously sustained.
Earmuffs can provide as much attenuation as can earplugs. An advantage of earmuffs is that they are easy to correctly place: whether they are properly inserted or installed is not an issue. Earmuffs are especially useful when exposure to noise is relatively intermittent.
Runway workers may need to put on and take off earmuffs many dozens of times a shift. These workers would not likely put earplugs in and out that frequently; if they did, many of those installations would probably be imperfect.
Earmuffs that permit normal hearing in the absence of a loud noise are now available. The muffs are able to detect the presence of a loud noise and attenuate it before it reaches the human ear. The most effective ear protection is the ear protection the person is willing to wear.
Phoon WH. Impact of statutory medical examinations on control of noise-induced hearing loss. Ann Acad Med Singapore. 1994 Sep;23(5):742-4.
