Ear Center: Noise Exposure
Noise Exposure: The Problem
Excessive Noise Causes Permanent Hearing Loss!
Excessive noise exposure is a very common cause of sensorineural (nerve-type) hearing loss. Hearing loss due
to noise is categorized as:
- noise induced hearing loss
- acoustic trauma
Noise induced hearing loss is due to repeated exposure to noise and is cumulative. Noise induced hearing loss is commonly caused by workplace noise, repeated exposure to loud music, portable electronic music/video players, rock concerts, etc. The hearing loss is painless and gradual. Importantly, for every 5 dB of exposure above 85 dB, hearing loss doubles in the high frequencies.
Acoustic trauma is defined as sudden exposure to very loud noise such as explosions, firearms, firecrackers, sudden loud industrial noises, military noise (military rifles, machine guns, grenades, bombs, artillery), and other very loud noises. Acoustic trauma may occur due to a single exposure to very loud noise. The hearing loss may be painful and is sudden in onset coinciding with the noise trauma.
Exposure to excessive noise, either cumulative or suddenly, can and does damage hearing. If the sound is loud enough and lasts long enough, irreversible sensorineural hearing loss will and does occur.
How Noise Damages Hearing
The ear is a transducer of sound. It transduces sound/noise traveling through the air into sound vibrations that travel through the inner ear fluid and stimulate small, delicate "hearing hair cells" (three rows of outer hair cells and one row of inner hair cells located in the Organ of Corti). Stimulation of the "hearing hair cells" of the inner ear causes electrical signals to be sent to the brain through the auditory nerve and the brain's central hearing pathways. Excessive noise or loud sounds literally leads to physical damage and ultimate destruction of the delicate "hearing hair cells". As more and more of the normal hair cell population becomes destroyed, more hearing is destroyed. In humans, once the hearing hair cells are destroyed, they never recover. The damage and resultant hearing loss are permanent.
As the cells are destroyed, the person first notices a decrease in loudness and then a decrease in the ability to understand words. The first hearing hair cells to be destroyed by chronic noise are those cells that are responsible for high frequency hearing. Commonly, the person will notice increasing difficulty hearing in groups or when there is competing background noise (noisy restaurants, more than one person speaking at the same time, etc.)
Sound is Measured in Decibels (dB)
Sound intensity or loudness is measured in decibels (dB). Because the human ear has a very large "dynamic range" for sound detection, i.e. can detect sound over a very wide range from very faint to very loud sounds, the decibel scale is a logarithmic scale. This means that increases in sound as measured in decibels are not linear but are exponential. In other words, an increase from 20 dB to 30 dB is not simply an increase in 10 units of sound. Because of the exponential increase, the change from 20 dB to 30 dB represents 3 1/2 doublings of the sound energy. Stated another way, 20 dB is 10 times the intensity of 10 dB., and 30 dB. is 100 times the intensity of 20 dB.
The human ear can detect frequencies of sound from 20 Hz (Hertz or cycles/sec.) to 20,000 Hz. Interestingly, cats can detect frequencies of up to 100,000 Hz. (the sound that a mouse makes!)
How Many Decibels are Too Many?
Continued exposure to sound intensities of 85 dB is dangerous and will cause irreversible hearing loss. For noise induced hearing loss, the longer the exposure to loud noise, the more damage occurs to hearing. In addition, the closer the noise source is to the ear, the more damage occurs.
OSHA (Occupational Safety and Health Administration) has developed recommendations for how much noise is permissible in the workplace and how long one can work in various levels of noise. For ears that are not protected by ear plugs, ear muffs, noise defenders, etc., the allowed exposure time decreases by one-half for each 5 dB. increase in the average noise level present. "Exposure is limited to 8 hours at 90 dB., 4 hours at 95 dB., and 2 hours at 100 dB. The highest permissible noise exposure for the unprotected ear is 115 dB. for 15 minutes/day. Any noise above 140 dB. is not permitted...individual hearing protectors are required when noise averages more than 90 dB during an 8 hour day."
Modern Electronic Devices
At this time, it is unknown how modern, portable electronic music/video players will affect hearing. When used at reasonable, comfortable volume settings less than 85 dB, the ear should not be damaged. However, when used at excessive volume settings (i.e. parents or bystanders can hear loud music from the insert earphones), damage to hearing would be anticipated and predicted. Prior to the advent of MP3 players, electronic devices could reproduce music for up to several hours. With the advent of massive storage capacities, electronic devices can play for very extended periods of time. Again, it is predicted that the extended duration of exposure to loud sounds, at or above 85 dB, will lead to irreversible hearing loss in a cumulative fashion.
Both noise induced hearing loss and acoustic trauma may cause ringing in the ears (tinnitus). With noise induced hearing loss, the ringing usually begins as a faint, constant ringing in both ears and usually becomes louder with time and cumulative noise exposure. Eventually, the ringing may become very loud, especially at night. Acoustic trauma may result in the onset of very loud ringing immediately after the sudden exposure. The ringing may be permanent and untreatable. If the ear begins to ring, the noise/sound is too loud. The ear is providing a warning signal to decrease the loudness. Permanent hearing loss may occur.
Loudness Level of Common Sounds
Typical Level (dB) Example Dangerous Time Exposure
- 0 dB = Faintest sound heard by the human ear
- 30 dB = Whisper, quiet library
- 40 dB = Quiet office, living room, bedroom away from traffic
- 50 dB = Light traffic at a distance, refrigerator, gentle breeze
- 60 dB = Normal conversation, sewing machine, typewriter
- 70 dB = Busy traffic, office tabulator, noisy restaurant. At this critical level, noise may begin to affect hearing if you are constantly exposed
- 80 dB = Subway, heavy city traffic, alarm clock at 2 feet, More than 8 hours factory noise
- 90 dB = Truck traffic, noisy home appliances, shop tools, lawnmower. As loudness increases, the safe time exposure decreases.
- 100 dB = Chain saw, boiler shop, pneumatic drill. Exposure Less than 2 hours without protection may be dangerous at 100 dB and with every 5 dB increase, the "safe time" is cut in half
- 120 dB = Rock band concert in front of speakers, sandblasting, Immediate danger, thunderclap. At 120 dB., exposure can injure the ear.
- 140 dB = Gun muzzle blast, jet engine at 50 feet. Noise at any length of exposure time injures unprotected ears. Maximum allowed noise with hearing protectors. 140 dB may cause pain and even brief exposure is dangerous.
- 180 dB = Rocket launching pad. Without ear protection, noise-induced hearing loss is inevitable. Noise at this level causes irreversible damage.
Protecting Your Ears
Hearing protectors are devices that are worn to protect ears from loud sounds. Hearing protectors come in two general varieties:
Earplugs are inserted into the outer ear canal and are available in many styles and colors. The important thing is that they fit snugly into the ear canal and seal the ear canal completely. If standard earplugs do not fit properly, custom earplugs can be made. Properly fit, high quality earplugs will reduce noise by 15-30 dB. and are better at blocking low frequency noise than are earmuffs
Earmuffs fit over the external ears and form an air seal. They are held in place by adjustable head bands and will not seal properly around eyeglass temples or long hair. Properly fit and adjusted earmuffs will reduce noise by 15-30 dB. and are better at blocking high frequency noise than are earplugs. Specialized earmuffs are available for firearm shooters that permit instructors to be heard but provide protection during shooting.
All hearing health professionals and parents want to help preserve their children's hearing. MP3 music players are wonderful devices, but many are capable of producing very loud volumes of sound for many hours. Noise induced sensorineural hearing loss (as well as acoustic trauma), in both ears, is a distinct possibility when excessive volumes are used.
In response to address the issue of excessive volumes, new earphones and headphones for MP3 players are now available from several manufacturers. The Ear Center of Greensboro, P.A. has not tested any of these devices and does not endorse any particular manufacturer. However, the following is a partial list of products for your review:
- Ultimate Ears LoudEnough Earphones loudenough.com
- iHearSafe Safe Volume Earbuds ihearsafe.com, etoys.com
- AirDrives for Kids apple.com, bestbuy.com, target.com
- iHearSafe Safe Volume Headphones ihearsafe.com
Combination Earplugs and Earmuffs
By wearing both earplugs and earmuffs together, noise can be reduced by an additional 10-15 dB. Both should be used if noise levels exceed 105 dB. The combination of earplugs and earmuffs is not essential. The important issue is that one wear one or the other, both if desired, to attenuate noise at 85 dB or louder.
- Rose AS, Ebert CS, Prazma J, Pillsbury HC. Noise exposure levels in stock car auto racing. Ear, Nose & Throat Journal, 87(12), 2008, 689-692.
- Athavely A. Protecting Little Ears from Their iPods. Newspaper article, Wall Street Journal, page D12, August 28, 2008.
- Keppler H, Dhooge I, Maes L, D'haenens W, Bockstael A, Philips B, Swinnen F, Vinck B. Short-term auditory effects of listening to an MP3 player. Arch Oto-HNS, 2010, 136(6), 538-548.
- Shargorodsky J, Curhan SG, etal. Change in Prevalence of Hearing Loss in US Adolescents. JAMA 2010; 304 (August 18):772-778.
- Derebery MJ, Vermiglio A, et al. Facing the music: pre- and postconcert assessment of hearing in teenagers. Otol Neurotol 2012:33 (September):1136-1141.
If you would like to:
- learn more about noise exposure
- how to protect your ears
- suspect that you might have noise induced hearing loss
- would like to have your hearing checked by highly skilled professionals
- would like to obtain custom earplugs
- would like information concerning specialized earmuffs
please contact our office at (336) 273-9932 for an appointment.
For additional information concerning noise exposure, hearing loss, and hearing protection, please visit this web site, . Offered by the American Academy of Otolaryngology-Head & Neck Surgery.
Last revised October 21, 2012