Noise Damage to the Inner Ear

Your ear receives sound waves and sends them through a delicately balanced system to the brain. Part of this remarkable system, the cochlea, is a chamber in the inner ear filled with fluid and lined with thousands of tiny hair cells. The hair cells signal the auditory nerve to send electrical impulses to the brain. The brain interprets these impulses as sound. When you are exposed to loud or prolonged noise, the hair cells are damaged and the transmission of sound is permanently altered.

How is our ability to hear sounds measured?

Humans are equipped with very sensitive ears capable of detecting sound waves of extremely low intensity. The faintest sound which the typical human ear can detect has an intensity of 1*10-12 W/m2. A sound with an intensity of 1*10-12 W/m2 corresponds to a sound which will displace particles of air by a mere one-billionth of a centimeter. WOW! This faintest sound which a human ear can detect is known as the threshold of hearing. The most intense sound which the ear can safely detect without suffering any physical damage is more than one billion times more intense than the threshold of hearing.

Hearing is measured in decibels (dB) and it is logarithmic.

Since the range of intensities which the human ear can detect is so large, the scale which is used to measure intensity is a scale based on multiples of 10. This type of scale is sometimes referred to as a logarithmic scale. The scale for measuring intensity (or noise level) is the decibel scale (dB). The higher the decibel level, the louder the noise.

The threshold of hearing is assigned a sound level of 0 decibels (abbreviated 0 dB); this sound corresponds to an intensity of 1*10-12 W/m2. A sound which is 10 times more intense ( 1*10-11 W/m2) is assigned a sound level of 10 dB. A sound which is 10*10 or 100 times more intense ( 1*10-10 W/m2) is assigned a sound level of 20 db. A sound which is 10*10*10 or 1000 times more intense ( 1*10-9 W/m2) is assigned a sound level of 30 db. A sound which is 10*10*10*10 or 10000 times more intense ( 1*10-8 W/m2) is assigned a sound level of 40 db.

The noise chart below gives an idea of average decibel levels for everyday sounds around you.

Intensity of Common Noises

Threshold (normal)

0 dB

Faint

10 dB = rustling leaves
20 dB = whisper
30 dB = quiet library

Moderate

40 dB = quiet room
50 dB = moderate rainfall

Very Loud

60 dB = normal conversation, dishwasher
70 dB = busy traffic, vacuum cleaner
80 dB = alarm clock, busy street, vacuum cleaner

Extremely Loud

90 dB = lawnmower, shop tools, truck traffic, subway
100 dB = snowmobile, chain saw, pneumatic drill, walkman, iPod
106 dB = timpani and bass drum rolls (large orchestra)
110 dB = rock music, model airplane

Painful

120 dB = jet plane take-off, amplified rock music at 4-6 ft., car stereo, band practice
130 dB = jackhammer
140 dB = firearms, air raid siren, jet engine
150 dB = rock music peak, shotgun
160 dB = nearby explosion, will result in rupture of ear drum

Keep in mind that conversational speech is approximately 60-65 dB, sounds louder than 80 decibels are considered potentially hazardous and the threshold of pain is considered to be 120-130 dB.

How noise damages the inner ear

There are three factors that can affect the danger of a noise to the health of the inner: its intensity, the distance of the person from its source, and the length of time exposed to it.

Sound Intensity

Sounds louder than 80 decibels are considered potentially dangerous. Examples of noise levels considered dangerous are a lawnmower, a rock concert, firearms, firecrackers, headset listening systems, motorcycles, tractors, household appliances (garbage disposals, blenders, food processors/choppers, etc.) and noisy toys (toys with horns and sirens, toy vacuum cleaners and vehicles, musical instruments, talking dolls, squeeze toys, and battery-operated toys that emit sounds). All can deliver sound over 90 decibels and some up to 140 decibels.

Distance

How far you are from the source of noise changes the intensity of the noise. Since sound waves are spreading out in the shape of a sphere, the sound is spread thin rapidly. Therefore, if the distance from the source is doubled, the intensity is not halved, but quartered (decreased by a factor of 4).

It is obviously better for your ears to sit further away from the speakers at a rock concert or listen to music from speakers, rather than headphones.

Noise Exposure

The other factor affecting the risk of noise exposure is the length of time you are exposed to the noise. Both the amount of noise (intensity) and the length of time of exposure determine the amount of damage. Hair cells of the inner ear and the hearing nerve can be damaged by an intense brief impulse, like an explosion, or by continuous and/or repeated exposure to noise. Noise induced hearing loss is usually gradual and painless, but, unfortunately, permanent. Once destroyed, the hearing nerve and its sensory nerve cells do not regenerate.

For example, the damage caused by one shot from a .357 magnum pistol, which can expose a shooter to 165 dB for 2msec, is equivalent to over 40 hours in a noisy workplace.

Warning Signs of Hazardous Noise

You must raise your voice to be heard
You can't hear someone two feet away from you
Speech around you sounds muffled or dull after leaving a noise area
You have pain or ringing on your ears (tinnitus) after exposure to noise.

Noise not only affects hearing. It affects other parts of the body and body systems. It is now known that noise:

Increases blood pressure
Has negative cardiovascular effects such as changing the way the heart beats
Increases breathing rate
Can cause an upset stomach or ulcer
Can negatively impact a developing fetus, perhaps contributing to premature birth
Makes it difficult to sleep, even after the noise stops
Intensifies the effects of factors like drugs, alcohol, aging and carbon monoxide

Other Changes

Noise can also hamper performance of daily tasks, increase fatigue, and cause irritability.

Noise can reduce efficiency in performing daily tasks at work by reducing attention to tasks. Researchers have also looked at the effect of excessive noise in school classrooms. Students whose classrooms face noisy streets do not do as well in school as students in classrooms facing away from noisy streets.

Noise also makes speech communication harder. More concentration and energy is needed not only to listen and hear over the noise but also to speak louder above the noise. As a result, voices can be strained and vocal cord abuses, such as laryngitis, develop.

From another perspective, your own inability to hear and understand others clearly can cause you to feel angry and frustrated. Instead of accepting the problem is yours, you misdirect your feelings to others and blow up at them.

Protect Yourself from Noise

The key word in dealing with noise is prevention.

Wear hearing protectors at work, during recreation (rock concerts, hunting, etc.) or at home (mowing the lawn, snow blowing the driveway, etc.). Cotton in your ears won't work. Hearing protectors include ear muffs and ear plugs (not swimmer's plugs). This protection can be purchased at drug stores or sporting goods stores. The most effective and satisfying solution are custom-fitted ear plugs which contain noise filters. These can be ordered through our office. (link to ear plugs in product section)
Limit periods of exposure to noise. Don't sit next to the speakers. If you are at a rock concert, walk out for awhile give your ears a break ! If you are a musician, wear ear protection--it is a necessity!
Turn down the volume! When using stereo headsets or listening to amplified music in a confined place like a car, turn down the volume. Remember: if a friend can hear the music from your headset when standing three feet away, the volume is definitely too high. Don't be afraid to ask others to turn down the volume.
Educate others and take action! Educate your children through discussion and by example. Wear your ear protection and encourage your children to follow your example.
Be a responsible consumer. Look for a noise rating when buying recreational equipment, children's toys, household appliances, and power tools. Choose quieter models, especially for equipment that you use often or close to your ears like a hair dryer.
Inspect your child's toys for noise danger, just as you do for small parts that can cause choking.
Have your hearing tested by one of our audiologists.
Be aware of the noise in your environment and take control of it when you can. Be an advocate for reducing noise pollution. For example, some schools have set a decibel limit for the music played at school dances in order to protect the students' hearing.

Workplace Noise

Many people are exposed to hazardous noise levels at work, including firefighters; military personnel; disc jockeys; subway workers; construction workers; musicians; farm workers; industrial arts teachers; highway workers; computer operators; landscapers; factory workers; and cab, truck, and bus operators, to name a few. And, they number nine million according to the U.S. Environmental Protection Agency (EPA).

Continued exposure to more than 85 decibels (dBA) of noise may cause gradual but permanent damage to hearing. Hearing loss is accelerated by louder noises.

Federal Occupational Safety and Health Administration (OSHA ) regulations require that, when engineering controls and/or administrative controls cannot reduce noise levels in industry to an eight-hour time-weighted average (TWA) level of less than 85 dBA, a hearing protection (or conservation) program must be established. A successful hearing loss prevention program benefits both the employee and the employer. Employees are spared disabling hearing loss and may experience less fatigue and better health in general. Employers benefit from reduced medical expenses and worker compensation costs. Overall, there is improved morale and work efficiency in the workplace.

OSHA requires a five phase hearing conservation program for industry:

1. Noise Monitoring

Sound levels must be measured. Results are used to decide: (a) which employees need to be in the hearing conservation program, (b) whether hearing protection devices must be used or be available on an optional basis, (c) which hearing protection devices are appropriate for different noise levels of the facility.

2. Audiometric (Hearing) Testing

All employees in a hearing conservation program must have baseline and annual hearing tests.

Baseline audiometric testing helps the employer to determine the presence or absence of a pre-existing hearing loss and may assist the employer in determining job placement for the employee.

Annual audiometric testing assesses the effectiveness of the hearing conservation program. Each annual audiometric test is compared with the emplpoyee's baseline test to determine if there has been any deterioration in the employee's hearing. There are no better alternatives than quality audiometric testing to determine if workers are protected from the damaging effects of noise.

3. Employee Training

Employees involved in a hearing conservation program must receive annual education and training on (a) the effects of noise on hearing, (b) hearing protection devices (their availability to employees, their advantages and disadvantages, techniques for proper selection, fit, use, and care) and, (c) the purpose and procedures of audiometric testing. By being involved in education, employees learn how to protect their hearing when exposed to loud noise, both on and off the job.

4. Hearing Protectors

Hearing protection devices should be made available to all employees. Mandatory versus optional use is determined by noise exposure monitoring. Hearing protection devices must be worn by employees whose eight hour TWA is 90 dBA or greater and by employees whose TWAs are between 85-90 dBA if they display standard threshold shifts in hearing levels. A standard threshold shift is defined by OSHA as "a change in hearing threshold relative to the baseline audiogram of 10dB or more for the frequencies 2000, 3000, and 4000 Hz in either ear." Hearing protection devices must meet sound recution levels required by OSHA.

5. Recordkeeping

Sound measurement results, equipment calibration results, and audiometric test records of employees must be maintained for specific periods of time.

The skills of a knowledgeable professional are essential to assure an effective and successful hearing conservation and protection program. For the audiometric testing phase, OSHA specifically requires supervision by an audiologist, otolaryngologist, or physician. As a professional with specialized training and expertise in all areas of hearing, the audiologist is able to assist and guide industry for better hearing health of employees.

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