By Peter Marincovich, Ph.D
Have you noticed that daily life in our society gets louder every year? The change is subtle and is a problem that most of us take for granted and even ignore. According to many leading Audiology professionals, casually ignoring the sounds around us can lead to serious hearing problems, including noise-induced hearing loss (NIHL).
One of those professionals is David Coffin, Audiology clinic coordinator at Indiana’s Ball State University. “We are exposed to all sorts of sounds that can lead to permanent hearing loss,” Coffin says. “The average person will wear a helmet when riding a bike, or a seat belt in a vehicle, but doesn’t even think about ear protection when going to watch a rock band, a fireworks display, or even an auto race.”
According to the Better Hearing Institute, 30 million Americans are exposed to dangerous noise levels each day and 10 million Americans have already suffered irreversible hearing damage from noise.
The problem of noise induced hearing loss has been around for decades. It occurs at home, in the yard, at the office, at the factory, on the farm and in the military. But today, because of technology, virtually everyone is effected and at younger and younger ages. It is not uncommon for audiologists to see 20-year-olds with the hearing of 60-year-olds.
However, there is good news as well: NIHL is easily identifiable and completely preventable. Today, audiologists can assist with the prevention, diagnosis and rehabilitation of hearing loss.
Normal conversations occur at approximately 60 decibels. Raising your voice over a noise in order to be heard by someone an arm’s length away is a good indication that the noise could be within risky range. Knowing which noises can cause damage, such as jet engines, lawn mowers, motorcycles, chainsaws, powerboats, and personal media players is the best arsenal against NIHL.
“Risky noise,” says Coffin, “can come in the form of the pop of fireworks, the snarls of traffic, the buzz of lawn mowers, or the percussive tones of marching bands.”
According to Coffin, such sounds are typically within the range of 90 to 140 decibels, but any noise above 80 can cause long-term hearing damage. The maximum exposure time per day for the exposed ear is 8 hours at 90 decibels. The risk of noise-induced hearing loss depends on both the intensity and duration of the exposure. As intensity increases, the length of time for which the exposure is “safe” decreases. For example, exposure to 85 decibels (often produced by gas-engine lawn mowers) for 8 hours can be as equally damaging as exposure to 110 decibels (often produced by a chain saw) for only a few minutes. For every 5 decibel increase in volume, the maximum exposure time is reduced by 50 percent. Therefore, according to Sight and Sound Associates, the maximum daily exposure time at 95 decibels is four hours; at 120 decibels, seven minutes, 30 seconds.
Warning signs that exposure to hazardous noise has occurred or is occurring include: the inability to hear someone a few feet away, ear pain after leaving a noisy area, ringing or buzzing (tinnitus) in the ears immediately after exposure to noise, or hearing people talking but being unable to understand them.
Loud explosions that peak for a few milliseconds at levels greater than 130 to140 decibels may cause hearing loss. More often, however, hearing loss is caused by repeated exposure to noise above 85 decibels over long periods. Some sources of common noises and associated decibels are: lawn mower, 90 decibels; stereo headphones, 105-110 decibels; automobile horn, 110 dB; baby’s cry, 115 decibels; rock concert, 115-120 decibels; and firearms, 125-140 decibels.
The commercial popularity of portable media players with earphones, such as the iPod and similar devices, and their long-term use by consumers, increase the risk of NIHL in those users. According to the National Center for Health Statistics, almost 15% of Americans below the age of 19 suffer from some measure of hearing loss. And according to Sight and Hearing Association, the incidents of teenage hearing loss has increased 400 percent over a ten-year period, as found in a recent study of eighth graders.
Symptoms of NIHL
NIHL usually develops gradually. People may lose a significant amount of hearing before becoming aware of its presence. The first sign of NIHL is not being able to hear high-pitched sounds, such as the singing of birds, or not understanding speech when in a crowd or an area with a lot of background noise. If damage continues, hearing declines further, and lower pitched sounds become hard to understand.
Signs of hearing loss from unsafe sound exposure include the inability to comprehend somebody talking from two feet away, hearing muffled speech, experiencing pain or ringing in the ears following exposure, and needing others to speak louder in conversation.
People often fail to notice the impacts of unsafe exposure to noise because it causes few symptoms. Hearing loss is rarely painful. Symptoms may go away minutes, hours or days after the exposure to noise ends. Many people naturally assume that if the symptoms abate, their ears have recovered to normal. However, even in the absence of more symptoms, some cells in the inner ear may have been destroyed by the noise. Hearing returns to normal only if enough healthy cells are left in the inner ear. But if the noise exposure is repeated and more cells are destroyed a lasting hearing loss will develop.
Sensorineural Hearing Loss
When the hearing system is exposed to noise at a risky or hazardous level, mechanical and metabolic changes can occur. Scientific research, based on studies of industrial workers, as well as lab studies of humans and animals, have investigated the effects of noise on hearing.
In these studies, excessive noise stimulated cells in the inner ear, resulting in chemical processes that can exceed the cells’ tolerance. This damages cell function and structure and results in sensorineural hearing loss (as opposed to a conductive hearing loss, where the outer or middle ear have been affected) and tinnitus (ringing of the ears).
The sensory cells in the cochlea may recover from their damage (as you have possibly experienced after a loud concert or work with a loud machine). Usually, recovery from temporary threshold shift (or TTS) occurs quickly, largely disappearing in 16 to 48 hours after exposure to loud noise. However, if the hearing sensitivity does not recover within a few days, an irreversible and permanent threshold shift has taken place.
Hearing loss is not reversible, but NIHL is preventable. Individuals vary in their susceptibility to hearing loss and hearing typically declines with age, but a healthy person who is not exposed to hazardous noises can enjoy normal hearing into his senior years.
Noise is probably the most common occupational hazard facing workers today. Employers at noise-hazardous workplaces, and physicians, are in a position to advise those at risk for developing NIHL that there are three simple keys to prevention:
- Understand what noises put them at risk – those above 85 decibels, commonly portable media players, lawn mowers, motorcycles, chain saws, jet engines, etc. A general rule of measurement is that if one has to shout to be heard an arm’s length away, assume the noise is above a hazardous threshold.
- If possible, decrease noise at the source – for example, keep the volume low on portable media players, purchase motorized equipment with an effective muffler, etc.
- Buffer loud noises with earplugs or other forms of hearing protection. These are known as hearing protective devices (HPDs) and are required by law to be labeled with a Noise Reduction Rating (NRR) based on performance obtained under ideal laboratory conditions. HPDs are powerful tools for preventing NIHL if worn correctly and throughout the duration of the hazardous noise. Also sound absorbing materials, such as floor mats, can help reduce noise.
Early identification is important in order to recognize the presence of NIHL and take steps to prevent further hearing loss. Those regularly exposed to hazardous noise in the workplace or elsewhere should have an annual hearing test. If hearing loss is developing, it might indicate under-protection and could suggest preventative measures, such as better HPDs or turning down the volume on the iPod
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