This document is a copy of the document at http://www.mckinley.uiuc.edu/health-info/dis-cond/misc/noiseeh.html (at least as of Jan 2003)
CAN NOISE BE DANGEROUS? CAN IT REALLY HURT MY EARS?
Yes -- noise can be dangerous. If it is loud enough and lasts long enough, it can damage your hearing. This type of damage, called "nerve loss", can be caused by several factors other than noise, but it is different in one important way -- it can be reduced or prevented altogether.
CAN I "TOUGHEN UP" MY EARS AGAINST LOUD NOISE IF I HEAR IT DAILY?
No. If you think you have grown used to a loud noise, it probably has damaged your ears, so that you do not hear as well as you once did. Surely, you don't want to toughen your ears by losing part of your hearing!
HOW DOES THE EAR WORK? HOW DOES NERVE LOSS OCCUR?
The ear has three main parts: the outer, middle, and inner ear. The outer ear (the part you can see) opens into an entryway called the ear canal. The eardrum separates the ear canal from the middle ear. Small bones in the middle ear help transfer sound to the inner ear. The inner ear contains the auditory (hearing) nerve, which leads to the brain.
Any source of sound sends out vibrations or sound waves into the air. These funnel through the ear opening and down the ear canal and strike your eardrum, causing it to vibrate. The vibrations are passed to the small bones of the middle ear, which in turn transmit them to the hearing nerve in the inner ear. Here, the vibrations become nerve impulses and go directly to the brain, which interprets the impulses as sound: music, a slamming door, a voice, etc.
When noise is too loud, it begins to kill the nerve endings in the inner ear. As the exposure time to loud noise increases, more and more nerve endings are destroyed. As the number of nerve endings decreases, so does your hearing. There is no known way to restore life to dead nerve endings; the damage is permanent.
HOW CAN I TELL IF A NOISE IS DANGEROUS?
People differ in their sensitivity to noise. As a general rule, noise may damage your hearing if you have to shout over background noise to make yourself heard, the noise hurts your ears, it makes your ears ring, or you are slightly deaf for several hours after exposure to the noise.
Sound also can be measured scientifically. We measure sound in two ways: Intensity, or loudness of sound, is measured in decibels. Pitch is measured in frequency of sound vibrations per second. A low pitch such as a deep voice or a tuba makes fewer vibrations per second than a high voice or a violin does.
WHAT DOES FREQUENCY HAVE TO DO WITH HEARING LOSS?
Frequency is measured in cycles per second, or Hertz (Hz). Young children, who generally have the best hearing, can often distinguish sounds from about 20 Hz, such as the lowest note on a large pipe organ, to 20,000 Hz, such as a high, shrill dog whistle that many people would be unable to hear at all. Human speech, which ranges from 300 to 4,000 Hz, sounds louder to most people than noises at very high or very low frequencies. When hearing impairment begins, the high frequencies are often lost first, which is why people with hearing loss often have difficulty hearing high-pitched voices of women and children.
Loss of high frequency hearing also can cause distortion of sound in the speech range. Someone whose hearing is impaired may confuse certain consonants, so that many words sound garbled. This is especially true of words that start with S, F, SH, CH, H, or a soft C, because the sound of these consonants is in a much higher frequency range than vowels and other consonants.
CAN YOU GIVE ME SOME EXAMPLES?
If you are losing high frequency sounds, words that rhyme and begin with higher frequency consonants (like "hill", "fill", and "sill") may sound exactly the same. You may need to have confusing words repeated or even spelled out, or guess at the meaning of whole sentences.
WHAT ABOUT DECIBELS?
Intensity of sound is measured in decibels (dB). The scale runs from the faintest sound the human ear can detect, which is labeled 0 dB, to over 180 dB, the noise at a rocket pad during launch. It is important to understand that decibels are not measured in the linear arithmetic that we normally use. For example, you know that a car going 60 mph is going twice as fast as one going 30 mph -- this is linear arithmetic. Decibels, on the other hand, are measured logarithmically. This means that as decibel intensity increases by units of 10, each increase is 10 times the lower figure. Thus, 20 decibels is 10 times the intensity of 10 decibels, and 30 decibels is 100 times as intense as 10 decibels.
HOW HIGH CAN THE DECIBELS GO WITHOUT AFFECTING MY HEARING?
Many experts agree that continual exposure to more than 80 decibels may become dangerous.
DOES THE LENGTH OF TIME I HEAR A NOISE HAVE ANYTHING TO DO WITH THE DANGER TO MY HEARING?
It certainly does. The longer you are exposed to a loud noise, the more damaging it may be. Also, the closer you are to the source of intense noise, the more damaging it is. Every gunshot produces a noise that could damage the ears of anyone in close hearing range. Large-bore guns and artillery are the worst, because they are the loudest. But even cap guns and firecrackers can damage your hearing if the explosion is close to your ear, and pistols are worse than rifles because the end of the barrel is closer to the ears. Anyone who uses firearms without some form of ear protection risks hearing loss.
IF I CAN'T AVOID NOISE, WHAT ARE THE BEST WAYS OF PROTECTING MY HEARING?
If you must be exposed to intense noise (even moderate noise for long periods), you should wear some kind of air-tight ear protector. There are two types: earplugs and earmuffs.
CAN'T I JUST STUFF MY EARS WITH COTTON?
Not unless you mean a pair of professional, wax-impregnated cotton earplugs. Ordinary cotton is much too porous to provide any protection at all. Professional earplugs are made of various materials: rubber, foam, wax-impregnated cotton, and plastic. Most sporting goods stores sell them at a modest price. They should be fitted separately for each ear, because each ear canal might be a different size. If both plugs fit snugly, they can provide about 15 dB of noise protection.
Well-fitted protective earmuffs screen out more noise than earplugs -- up to 25 dB. (However, you cannot wear muffs over glasses without a sound-leak occurring). Hearing specialists recommend muffs for anyone who works in construction, mining, lumber, or any other noisy job. Muffs can also provide protection for target shooters, hunters or anyone who uses power tools or noisy yard equipment. A combination of earplugs and earmuffs will give you the most protection.
WON'T EARMUFFS OR EARPLUGS KEEP ME FROM HEARING THE DOORBELL OR CONVERSATION?
Not at all. You will be able to hear a telephone, conversation or the doorbell. What you will notice is a reduction in background noise. In fact, some people with high-pressure jobs wear ear protectors just because the quieter atmosphere helps them concentrate.
WHAT IF MY HEARING IS ALREADY DAMAGED? HOW CAN I TELL?
Hearing loss usually develops over a period of several years. Since it is painless and gradual, you might not notice it. What you might notice is a ringing or other sound in your ear (called "Tinnitus"), which could be the result of long-term exposure to noise that has damaged the hearing nerve. Or, you may have trouble understanding what people say; they may seem to be mumbling. This could be the beginning of highfrequency hearing loss.
If you have any of these symptoms, you may have nothing more serious than impacted wax or an ear infection which might be simply corrected. However, it might be a nerve-type hearing loss. In any case, take no chances with noise -- the hearing loss it can cause is permanent. If you suspect hearing loss in yourself or a member of your family, consult a physician with special interest in caring for ear and hearing disorders (called an otolaryngologist or otologist). The doctor can diagnose your hearing problem and recommend the best way to manage it.
WHAT IS AN OTOLARYNGOLOGIST -- HEAD AND NECK SURGEON?
An otolaryngologist is a Doctor of Medicine who specializes in the care of disorders of the head and neck, especially those related to the ear, nose and throat. Otolaryngologists perform a great variety of surgical procedures in the daily treatment of the ear, nose, sinuses, pharynx, larynx, oral cavity, neck, thyroid, salivary glands, bronchial tubes and esophagus, as well as cosmetic surgery of the head and neck region. All otolaryngology specialists have been trained in cases such as adenoidectomies, tonsillectomies, nosebleeds, infected mastoids and sinus diseases, although not all continue to practice in all of these areas. Most have up-to-date audiologic equipment to test hearing and diagnose the cause of hearing loss. Many also treat speech and communicative disorders. Others have a special interest in problems of balance or allergic disorders of the upper respiratory system.
Those specially trained in ear work are well-equipped to restore hearing through modern microsurgery. Modern surgical techniques by this specialist can also cure disease and infection, and repair deformities present in the ear since birth. With their extensive knowledge of the head and neck, many otolaryngologists are proficient in facial plastic surgery and choose to specialize in cosmetic procedures. Otolaryngologists' training includes planning and carrying out the surgery and treatment of benign tumors as well as cancer of the head and neck, and the reconstructive techniques so necessary to restore form and function in these patients.
DECIBEL RATINGS AND HAZARDOUS TIME EXPOSURES OF COMMON NOISES Typical Dangerous Level Time (Decibels) Example Exposure 0 Lowest sound audible to human ear -- 30 Quiet library, soft whisper -- 40 Quiet office, living room, bedroom away from traffic -- 50 Light traffic at a distance, refrigerator, gentle breeze -- 60 Air conditioner at 20 feet, conversation, sewing machine -- 70 Busy traffic, office tabulator, noisy restaurant. At this decibel level, noise may begin to affect hearing if you are constantly exposed. Critial level begins 80 Subway, heavy city traffic, alarm clock at 2 feet, factory noise. More than 8 hours 90 Truck traffic, noisy home appliances, shop tools, lawn-mower. As loudness increases, safe time exposure decreases. Less than 8 hours 100 Chain saw, boiler shop, pneumatic drill. Exposure may be dangerous at 100 dB, and with every 5 dB increase, the "safe time" is cut in half. 2 hours 120 Rock band concert in front of speakers, sandblasting, thunderclap. At 120 dB, exposure can injure the ear. Immediate danger 140 Gunshot blast, jet plane. Noise at 140 dB may cause actual pain in the ear. Any length of exposure time is dangerous 180 Rocket launching pad. Without ear protection, noise at this level causes irreversible damage. Hearing loss inevitable
Permission to reprint by:
American Academy of Otolaryngology -- Head and Neck Surgery, Inc. 1101 Vermont Avenue, N.W., Suite 302 Washington, D.C. 20005
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(c) The Board of Trustees of the University of Illinois, 1995
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Copyright W G Unruh