Ear, Nose and Throat - U.S.A.  (ENT USA) Noise Induced Heairng Loss - Occupational Hearing Loss
Noise Induced Hearing Loss (NIHL)
Noise Induced Hearing Loss (NIHL)
Occupational Hearing Loss
  
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Nose Induced Hearing Loss is the is the second most common cause of hearing loss.  Much can be done to prevent noise-induced hearing loss but little can be done to reverse it.  Sometimes a single exposure to loud noise is all that is needed, a single hunting trip without ear plugs.  Loud noise damages the hair cells in the inner ear and can cause hearing loss, ear ringing and distortion of sounds.   

Download PDF on Occupational Hearing Loss
 
Hearing Handicap Calculator



To learn more about occupational hearing loss, presbycusis, hearing handicaps and noise exposure go the the
FLASH enhanced website
www.occupationalhearingloss.com

   

 
The symptoms of noise induced hearing loss are subtle in the early stages.  Hearing loss tends to occur first for high-pitched sounds only.  Consequently, the volume of sound heard may be unchanged but the quality of it lessens.  Speech may be heard but not completely understood.  The presence of background noise can make speech hard to understand.  Noise induced hearing loss can be accompanied by a ringing in the ears (tinnitus).  Tinnitus can often be more annoying than the hearing loss itself.  Treatment of tinnitus is often unsatisfactory.  

The economic effects of noise trauma can be staggering.  According to the Associated Press (March 2008) the Department of Veteran Affairs in 2006 spent $539 million dollars on veteran disability caused by tinnitus from noise induced hearing loss.   Hearing loss is the number one disability of the Afghan and Iraq wars.   58,000 soldiers have been disabled due to hearing loss and 70,000 soldiers are receiving disability payments for tinnitus. 

Decibel Levels of Environmental Sounds

Source dBA SPL
Discomfort Level Above 80
Heavy Traffic 80 
Automobile  (at 20 meters) 70
Vacuum Cleaner 65
Conversational Speech (at 1 meter) 60
Quiet Business Office 50
Residential Area at Night 40
Whisper, Rustle of Leaves 20
Rustle of Leaves 10
Threshold of Audibility  0
Source--Dangerous Level dBA SPL
Produces Pain  120-140
Jet Aircraft During Takeoff (at 20 meters) 130
Snowmobile
Tractor Without Cab
120
Rock Concert 110
Die Forging Hammer
Gas Weed-Whacker
Chain Saw
Pneumatic Drill
100-105
Home Lawn Mowers 95 to 100 dB
Semi-trailers (at 20 meters) 90


What Noises are Dangerous?

Physical measurements of the sound can be make to determine whether it exceeds dangerous levels, and most factories have access to the necessary equipment.  Radio Shack also sells a sound level meter for under $40 which will measure noise levels using the "A" Scale.  (This is what the designation dBA refers to -- decibels measured in the A Scale.)  However, without noise-measuring equipment, the following basic rules can be followed:

#1.  If it is necessary to shout to hear yourself over a noise, the level of the sound can be damaging.

#2.  Should ringing in the ears occur after exposure to a loud sound, damage has been done and that sound should be avoided or ear protection used in the future.

#3.  If diminished hearing or a sense of fullness in the ears is experienced after  noise exposure, the level of that noise is damaging.

Duration of Exposure (hrs/day)

Sound Level dB(A)

ACGIH NIOSH OSHA
16 82 82 85
8 85 85 90
4 88 88 95
2 91 91 100
1 94 94 105
1/2 97 97 110
1/4 100 100 115*
1/8 103 103 ---
  ***   **

*   No exposure to continuous or intermittent noise in excess of 115 dB(A).
**  Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure level.
*** No exposure to continuous, intermittent, or impact noise in excess of a peak C-weighted level of 140 dB.
 

Maximum Recommended Noise Exposure
  NIOSH 1997 and ACGIH 
 Enter Decibels: 
Maximum Recommended Noise Exposure
  OSHA 
 Enter Decibels: 

 
 

 
There are also many agents found in industry can also damage hearing in addition to industrial noise exposure.  The most common is tobacco
View Abstract
   
  • Industrial Solvents:  The combination of solvents and noise exposure exceeds the damage produced by either also.  The effect of solvents is potentiated even more by exposure to ethanol.   View Abstract
    Organic Solvents found in Industry which are ototoxic include.

--Toluene:  Found in paints, thinners, rubbers and in the printing industry. View Abstract
--Stryene:  Found in plastics, rubbers, resins, insulating materials. 
--Carbon Disulfide:  Found in the textile industry and insecticides.
View Abstract
--Tricholoroethylene: 
View Abstract
--Xylene:  Found in paint and lacquer industry
View Abstract


earplugs.jpg (29066 bytes)
Prevention     Search PubMed for Ear Plugs

Since little can be done to treat long standing noise induced hearing loss, the best prevention is to avoid loud noises.  Compressible foam ear plugs (not water plugs) and ear muffs can decrease the noise exposure level by over 20 dB.  Ear plugs and ear muffs are about equally effective.  Muffs cost more but can be used in patients with ear canal disease. Muffs are also hot in warm weather.  For hunting, electronic plugs and muffs can be obtained which make surrounding noise louder so game can be heard, but when firing a gun they muffle the loud noise. 
 
Many people will not wear ear plugs in a noisy environment because they think it will make it more difficult to hear others talking.  Actually the reverse is true.  Ear plugs reduce noise most efficiently in the low frequencies, below the speech range.  This will increase the signal to noise ratio of the speech and makes it more easily heard.
 
New research indicates that several types of drugs when taken before or immediately after noise exposure may mitigate the damage to the
inner ear.  These drugs fall into three categories:

  • Anti-oxidants:  These drugs may be protective based on the theory that one of the mechanisms in noise inducted hearing loss is the generation of free oxygen radicals.  Vitamin E given at 10mg/kg/day to 40mg/kg/day in the guinea pig was protective.  View Abstract ;  Acetyl-L carnitine View Abstract a mitrochondrial stabilizer for damage induced by free oxygen radicals, and N-L-acetylcysteine View Abstract , an antioxidant, has been shown to mitigate noise induced hearing loss in the chinchilla.  

    Glutathione is an antioxadant which has been show to reduce the damage of noise exposure.  View Abstract  Researchers have also found that noise induced hearing loss is characterized by a glutathione deficiency state and increase glutathione levels may be protective.  View Abstract    Glutathione monoethylester and in combination with R-N6-phenylisopropyladenosine has also been studied in the chinchilla and has been found to be protective.  View Abstract 
     
  • Glutamate Receptor Antagonist:  These drugs may be protective based on the theory that one of the mechanisms in noise induced hearing loss is the generation of Glutamate which binds to post-synaptic glutamate receptors which leads to degeneration of the neurons.   Investigated drugs include:  caroverine View Abstract ; carbamathione  View Abstract
        
  • Neurotrophins:  There is also evidence that neurotrophins (neurotrophin-3) may also be protective. View Abstract
      

Remember the most common outcome to noise exposure is a permanent hearing loss.  When this occurs the only effective treatment is the use of hearing aids.  This is why prevention by avoiding loud noises and wearing ear protectors is so important.

     
Other References: 
 

Franks JR.  Four Earplugs in search of a rating system.  Ear & Hearing.  21:218-226, 2000.
                  

Phoon WH, Lee HS, and Chia, SE.  Tinnitus in noise-exposed workers.  Occup Med 43:35-38. 1993.
      

 
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