Toxic Noise

Hearing loss afflicts approximately 28 million people in the United States. Approximately 10 million of these impairments are at least partially attributable to damage from exposure to loud sounds.

How Do We Hear?
Humans hear via highly specialized cells in the ear called hair cells. When sound enters the ear, the eardrum transmits it through the three middle ear bones --the malleus, the incus and the staples- to the cochlea of the inner ear. The cochlea is filled with fluid and conducts vibrations into the basilar membrane, which covers the cochlea and is lined with hair cells. The hair cells transform the vibrations into electrical signals (neural signals). These signals are passed on to the auditory nerve, and conducted to the brain where they are interpreted.

All the elements of the hearing mechanism are delicate, but hair cells are especially fragile. Hair cells differentiate from other cells in the body and begin to perform their special function while the fetus is still in the womb. No new hair cells are made after a child is born - the 30,000 hair cells that are created in vitro are the only ones a person will ever have. Loud noises can destroy these hair cells permanently and cause damage to the nerve of hearing.

What Sounds Cause Noise-Induced Hearing Loss (NIHL)?
NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period of time. The loudness of sound is measured in units called decibels. For example, usual conversation is approximately 60 decibels, the humming of a refrigerator is 40 decibels and city traffic noise can be 80 decibels.

Hair cells and the nerve of hearing can be injured by noise in two different ways: from an intense brief impulse, such as an explosion, or from continuous exposure to noise, such as that in a woodworking shop.

What Are the Effects of NIHL?
The effect from impulse sound can be instantaneous and can result in an immediate hearing loss that may be permanent. The structures of the inner ear may be severely damaged. This kind of hearing loss may be accompanied by tinnitus, an experience of sound like ringing, buzzing or roaring in the ears or head, which may subside over time. Hearing loss and tinnitus may be experienced in one or both ears, and tinnitus may continue constantly or intermittently throughout a lifetime.

The damage that occurs slowly over years of continuous exposure to loud noise is accompanied by various changes in the structure of the hair cells. It also results in hearing loss and tinnitus. The symptoms of NIHL that occur over a period of continuous exposure increase gradually. Sounds may become distorted or muffled, and it may be difficult for the person to understand speech. The individual may not be aware of the loss, but it can be detected with a hearing test.

Exposure to impulse and continuous noise may cause only a temporary hearing loss. If the hearing recovers, the temporary hearing loss is called a temporary threshold shift. The temporary threshold shift largely disappears within 16 hours after exposure to loud noise.

Toxic Noise Environment
Noise is all around us. At unsafe decibel levels, exposure to loud noise can be toxic and permanently damage hearing. There are four main environments in which we are at risk for exposure to toxic noise: workplace, home, recreation and travel.

Workplace:

Hearing loss is one of the most common occupational injuries in the United States. More than 30 million workers are regularly exposed to toxic noise and an additional nine million are at risk for hearing loss from other agents such as solvents and metals. Hearing loss is the second most self-reported occupational illness or injury.

Among the occupations at risk for hearing loss are police officers, fire fighters, construction workers, formers, military personnel, and musicians. While office environments tend to be less hazardous, any setting that involves heavy machinery can be toxic to the hearing.

Home:

Our homes are filled with noisy appliances. With dishwashers, vacuum cleaners, food processors, coffee grinders, and garbage disposals, the kitchen or living room can easily become the noisiest setting in our daily lives.

Most of these appliances do not by themselves produce hazardous levels of noise. When two sounds of equal volume are emitted simultaneously, however, the effect is a 3-5 decibel increase in overall noise. Considering that many people use three or four appliances simultaneously, background noise in the home can quickly reach toxic levels. Compounding the problem is our habit of turning up the volume on the radio, stereo, or television to hear over noisy appliances.

Recreation:

Sporting Events: Noise levels in stadiums and arenas can exceed 110 decibels. This is most frequently caused by crowd noise, although music and announcements can contribute to the decibel level.

Target shooting: Any sound above 140 dBA causes immediate acoustic trauma and instantaneous hearing loss. Gunshots typically produce decibel levels of at least 160 dBA.

Rock concerts: It is common for contemporary rock concerts to be played at levels exceeding 120 decibels. During these events, without proper hearing protection this can cause damage to your hearing.

Travel:

Traveling and commuting often put us into environments in which we can be at risk for hearing loss. Buses, planes, cars, and trains all produce dangerous levels of toxic noise. Even common sounds like city traffic can be hazardous to a person’s hearing over long periods of time.

Subways: Although the noise level varies by city, underground and elevated trains often produce sounds of 100 decibels or louder. The New York City subway was recently measured at 112 decibels, a level, which might causes permanently hearing loss.

Airplanes: Airline cabin noise varies depending on the type of plane, usually between 95 and 105 decibels. Passengers seated in the back of the plane may experience higher noise levels, and all passengers should be aware that engine noise during take-off could be upward of 115 decibels.

Automobiles: Prolonged exposure to ordinary city traffic - trucks and buses produce engine noise of 90 decibels or more - can be damaging to person’s hearing. In addition to the sounds of ordinary vehicles, urban residents are often bombarded by fire and ambulance sirens, which produce sounds of 120 decibels or greater.

Other Effects of Noise
Sleep: Noise is one of the most common forms of sleep disturbance. A study used by EPA showed that sleep interference was the most frequently cited activity disrupted by surface vehicle noise (BBN, 1971). Aircraft noise can also cause sleep disruption, especially with the escalation of nighttime operations by the air cargo industry. The EPA identified a nighttime average sound level of 35 dB as necessary to protect against sleep interference.

Learning: Studies have shown that children who attend schools that experience frequent airport noise do not learn to read as well as children who attend quiet schools. This occurs because at a very young age these children learn to tune out speech along with airplane noise. As a result, when they get older these children often have trouble learning to recognize and differentiate between speech and sounds.

Presbycusis: As they grow older, some individuals experience a gradual loss of hearing, known as presbycusis, but this should not be construed to mean that hearing loss is part of the natural aging process. Despite the fact that nearly 50% of people over 75 have a hearing loss, studies show that ¾ of the hearing loss in the typical person in the United states is due to the cumulative effects of toxic noise. Furthermore, health professionals do not recommend adjusting individual audiograms based on age, because this can result in a non-diagnosis of noise-induces hearing loss.

Can NIHL Be Prevented?
Noise-induced hearing loss is preventable. All individuals should understand the hazards of noise and how to practice good health in everyday life.

• Know which noises can cause damage (those above 75 decibels)
• Wear earplugs or other hearing protective devices when involved in a loud activity (special earplugs and ear muffs are available at hardware stores and sporting good stores)
• Be alert to hazardous noise in the environment
• Protect children who are too young to protect themselves
• Make family, friends and colleagues aware of the hazards of noise.

Have a medical examination by an otolaryngologist, a physician who specializes in diseases of the ears, nose, throat, head and neck, and a hearing test by an audiologist, a health professional trained to identify and measure hearing loss and to rehabilitate persons with hearing impairments.

Additional information can be found at the following organizations:

American Academy of Audiology

American Academy of Otolaryngology - Head & Neck Surgery

American Auditory Society

American Speech-Language-Hearing Association

American Tinnitus Association

Self Help for Hard of Hearing People Inc. (SHHH)

Sources: National Institute of Deafness and Other Communication Disorders, 2000
The National Campaign for Hearing Health at www.hearinghealth.net
Center for Disease Control/National Institute for Occupational Safety and Health at
www.cdc.gov/niosh/noise/noisepg.html and www.cdc.gov/niosh/98-126a.html
The League for the Hard of Hearing at www.lhh.org/noise/facts/index.htm