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Workers may be exposed to dangerously high noise levels in a variety of jobs and in virtually every workplace.  Whether the job is a clerical position in an office environment, a heavy equipment operator in a landfill, or a lab worker in a hospital, noise is everywhere and Noise-Induced Hearing Loss is a serious consequence affecting the health of all employees.

Hazards of Noise:

1.  Hearing Loss:

Intense noise may result in temporary or permanent hearing loss.

After a day in an excessively noisy environment, workers may experience temporary hearing loss.  A temporary hearing loss occurs when the nerves in the inner ear become tired and strained and fail to send messages to the brain.  Normal hearing will return if the workers remain in a quiet environment and allow their hearing to recuperate.

After years in an excessively noisy environment without any hearing protection, workers may experience permanent hearing loss.  A permanent hearing loss occurs when the nerves and cells in the inner ear become so damaged that they can no longer function properly.  This prevents any messages from getting to the brain. 

Normal hearing will never return.

Permanent hearing loss does not have to mean deafness.  Many workers have permanent hearing loss in specific frequency ranges.  This might prevent them from hearing high frequency sounds or low frequency sounds.  These loses could interfere with a worker’s ability to understanding speech or function normally in society.  Some workers lose their hearing over such a large range of frequencies that they are essentially deaf.

2.  Other Health Effects:

Noise can also cause stress and increased blood pressure, and may contribute to heart disease and ulcers.  Working in a noisy environment for long periods of time can make workers tired, nervous, and irritable.  Noise has also been linked to insomnia and loss of appetite.

Noise may also be a safety hazard.  Excessive levels of noise interfere with talking and hearing on the job.  Communication difficulties can cause accidents in the workplace.  Prolonged intense noise causes fatigue, which may also contribute to accidents.

Measuring Sound:

It is not necessary to use complicated equipment to tell if the level of noise is excessive and possibly damaging to hearing.  Workers may be exposed to dangerously loud noise if:

Sound level is measured with a sound level meter and is expressed in terms of decibels.  The decibel, abbreviated dBA, is the unit of measurement used to measure sound.  It is important to understand that the decibel scale is not an arithmetic scale (1,2,3…).  Rather, it is a logarithmic scale (101, 102, 103,…).  The decibel is based on the logarithm of the ratio of a measured quantity to a reference.  To summarize, this means that an increase in the dBA level is much more intense than it would appear.  For example a decibel level of 90 dBA is equal to 1 milliwatt (mW) of sound power, but three times this sound power (3 * 1 mW = 3 mW) is equal to an increase of only 5 decibels, 95 dBA.

Most noise standards recognize a three-decibel “exchange rate”.  The exchange rate is the decibel level that equals a doubling of energy or pressure therefore, it is also called a “doubling rate”.  This means that an increase of 3 dBA is equal to doubling the sound pressure.  Or by reducing the sound pressure level by 3 dBA, the noise “dose” would be cut in half.  Therefore, an increase or decrease of three decibels is significant.

In the OSHA standard, a five-decibel “exchange rate” is used.  That is, an increase of five decibels results in a doubling of the energy of the noise.  And a reduction of five decibels results in reducing the “dose” by half.  A practical example is as follows:  OSHA allows exposure to 90 dBA for 8 hours, however if the noise level is increased by 5 dBA to 95 dBA, OSHA only allows exposure for half the time, 4 hours (8/2 = 4).

Continuous, Intermittent and Impact Noise:

A continuous noise is a sound that is relatively constant.  An intermittent noise is one that has perceptible gaps between repetitions.

Impact noise is like a gunshot.  Tools such as jackhammers, air-driven tampers, and other pneumatic tools are the classic examples of equipment that generate impact noise.  Impact noise is often more harmful to the human ear than continuous or intermittent noise.

Controlling Noise Hazards:

Methods of reducing noise levels in the workplace include the use of engineering controls, work practices, and personal protective equipment as listed below:

For more information on the requirements of the OSHA standard 1910.95 please refer to the IBT Safety and Health Department Fact Sheet entitled Hearing Conservation and Occupational Noise Exposure.