Noise: Its effects on hearing and tinnitus

THE PROBLEM

Noise is, by definition, unwanted sound and varies in its composition in terms of frequency, intensity and duration. Sounds which are pleasing to some people may be unpleasant to others. For example, loud rock music is enjoyable to some but others find it offensive. Thus, for a sound to be categorized as noise, it must be judged as such by the listener.

PROTECT YOUR EARS FROM NOISE

Many of the sounds in our environment which we classify as noise are annoying but are not loud enough to cause damage to the hearing mechanism. Other sounds, however, are of such high intensity that they are potentially dangerous to the ear and may cause permanent hearing loss and or tinnitus Noise is everywhere! We cannot escape being exposed to it. However, preventative measures can be taken to limit the chance of damaging our ears from exposure to excessively loud noise.

NOISE INDUCED HEARING LOSS

Common knowledge indicates that continuous exposure to high levels of noise can cause hearing impairment in some individuals. There is considerable variation from person to person regarding susceptibility to noise; however, standards have been established which, on the average, indicate how much sound a person can tolerate without experiencing damage to their hearing. Although this level remains somewhat controversial, it has been established that most people will not experience a hearing loss if the noise levels do not exceed 85 to 90 dBA. Therefore, the Occupational Safety and Health Act established criteria based upon an 8 hour duration of exposure to a 90 dBA level of continuous noise. It was felt that this criteria would protect approximately 90% of the people exposed to 90 dBA levels for a significant part of their lifetime. For shorter durations of exposure, higher noise levels are permissible under this regulation.

TABLE 1 PERMISSIBLE NOISE EXPOSURES
Duration per day (hours)		Noise level (dBA)
8 6 4 3 2 1 1/2 1 3/4 1/2 1/4 or less	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	90 92 95 97 100 102 105 107 110 115

DANGER! NOISE CAN HURT YOU

Many sounds in our environment exceed the OSHA standards and continuous exposure to these sounds could cause loss of hearing. A sample of common noise sources is shown in Figure 1 along with their approximate sound pressure levels.

Figure 1 - Noise Thermometer
Published courtesy of BRUEL & KJAER Instruments Inc

Note: " µPa" refers to Micro Pascals, the units of sound pressure used to measure the intensities of sounds; "dB" or decibels to the relative intensities of sounds on the commonly used logarithmic scale.

The typical hearing loss observed with patients who have a long history of noise exposure is characterized by a loss of hearing in the frequency range between 3000 and 6000 Hz (See Figure 2). In the early stages of exposure, a temporary loss will be observed at the end of a working period but will disappear after several hours. Continuous exposure to the noise will result in a permanent hearing loss which will be progressive in nature and becomes subjectively noticeable to the employee over time. These changes in hearing thresholds can be monitored through audiometric testing and will alert clinicians that preventative measures should be initiated. In its advanced stages, a loss of hearing in the high frequencies will seriously affect the person's ability to understand normal speech. In general, the patients with hearing losses limited to the high frequencies will not experience difficulty detecting speech, but have trouble understanding conversation.

Figure 2 - Typical Audiogram of Ptient with Noise Induced Hearing Loss

(Note: Hz = Hertz, a unit of frequency equal to one cycle per second)

NOISE INDUCED TINNITUS

Although one can never make a definitive statement regarding the exact cause of tinnitus, many patients who have a history of noise exposure have tinnitus. Noise is by far the most probable cause of tinnitus which may or may not occur with an associated hearing loss. Most patients who have tinnitus also have hearing problems. However, a small percentage of tinnitus patients (approximately 10%) have hearing sensitivity within normal limits. Since many patients have hearing losses without tinnitus, it is not surprising that some patients with tinnitus have no hearing impairment.

It is reasonable to assume that any one of the four symptoms associated with ear pathologies - hearing loss, tinnitus, dizziness, or a feeling of fullness in the ear - could occur individually or without other symptoms.

The onset of tinnitus resulting from noise exposure can occur suddenly or very gradually. A very loud sound in the near vicinity of a person can result in tinnitus which can be either temporary or permanent. In cases where the tinnitus occurs suddenly, it is often perceived immediately as a fairly loud sound which may persist at that level.

More commonly, the onset of tinnitus is gradual and is most often intermittent in its early stages. Patients report hearing a mild form of tinnitus for a short period of time following a lengthy exposure to loud sounds. Once removed from the noise source, the tinnitus soon disappears and is inaudible until the next exposure. This intermittent pattern often continues for months or years with the periods of tinnitus becoming longer and longer until the tinnitus eventually becomes constant. Further exposure to the noise will often aggravate the problem and oftentimes continued exposure will cause the tinnitus to become sufficiently loud to be distressing and to interfere with the quality of life.

Most patients who have a long history of noise exposure complain of tinnitus which is tonal in quality and high-pitched. Of 153 clinic patients who reported having tinnitus as the result of being exposed to high intensity noise, 141 or 92.2% of them matched their tinnitus to the external tones above 3000 Hz. Most often, the tinnitus is bilateral but occasionally patients observe tinnitus only on one side.

HEARING CONSERVATION PROGRAM

Individuals exposed to noise levels which are potentially damaging to the ears, should initiate a hearing conservation program to reduce the noise to a permissible level. This reduction can be accomplished in one of three ways:

1. reduce the noise at its source.
2. reduce the amount of time the person is exposed to the noise.
3. provide personal hearing protection for the patient.

OSHA has mandated that Hearing Conservation Programs be initiated if noise levels exceed 85 dBA. Many companies have developed programs within those guidelines but others have not. Furthermore, due to differences in susceptibility to noise, some people may develop hearing loss and/or tinnitus from noise levels below 85 dBA. There are no published levels of noise which are known to induce tinnitus but, again, these levels appear to vary from patient to patient. It is also common for patients who already have tinnitus to observe an exacerbation of their tinnitus whenever they are exposed to noise. Shortly after being removed from the noise, the tinnitus will return to its original level. However, over time the loudness level of the tinnitus can gradually increase unless the ear is protected. Therefore, it is important for people who begin to observe a mild loss of hearing ort tinnitus to take the initiative to implement a hearing conservation program for themselves. Personal hearing protective devices are available from safety equipment suppliers and also from hearing product distributors. These devices come in many different forms and are reasonably priced. If used properly, they can safeguard the ears against further damage.

HOW TINNITUS AFFECTS YOU

Many people with tinnitus report that they have had to curtail social activities. Some tinnitus sufferers have had to quit work or change their jobs. Many report that they can no longer attend functions that are known to be noisy such as concerts (both rock and classical), dances, loud parties, and sporting events. They sometimes are unable to utilize various forms of transportation such as motorcycles, speedboats, airplanes, trucks, busses and sports cars. They may not be able to use chainsaws, lawnmowers, vacuum clears, food processors, electrical tools, and noisy appliances.

OTHER HEALTH CONSEQUENCES OF NOISE EXPOSURE

Noise can contribute to circulatory, respiratory, digestive and psychological ailments. Continued exposure may cause fatigue, headaches, increased pulse rate, stomach disorders, increased respiration, and high blood pressure. Noise is also suspected to interfere with children's learning and with normal development of the unborn child. These effects can remain even when the people think they have become used to the noise!