What Happens When Sound Enters the Ear?
Posted by Liz Ernst on Thu, Aug 04, 2011 @ 09:28 AM
Every year, approximately 30 million people in the United States are occupationally exposed to hazardous noise. Noise-related hearing loss has been listed as one of the most prevalent occupational health concerns in the United States for more than 25 years. Thousands of workers every year suffer from preventable hearing loss due to high workplace noise levels. Since 2004, the Bureau of Labor Statistics has reported that nearly 125,000 workers have suffered significant, permanent hearing loss. In 2009 alone, BLS reported more than 21,000 hearing loss cases.
Exposure to high levels of noise can cause permanent hearing loss. Neither surgery nor a hearing aid can help correct this type of hearing loss. Short term exposure to loud noise can also cause a temporary change in hearing (your ears may feel stuffed up) or a ringing in your ears (tinnitus). These short-term problems may go away within a few minutes or hours after leaving the noisy area. However, repeated exposures to loud noise can lead to permanent tinnitus and/or hearing loss.
When no sound barrier is in place, loud noise can also create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals. Noise-induced hearing loss limits your ability to hear high frequency sounds, understand speech, and seriously impairs your ability to communicate. The effects of hearing loss can be profound, as hearing loss can interfere with your ability to enjoy socializing with friends, playing with your children or grandchildren, or participating in other social activities you enjoy, and can lead to psychological and social isolation.
When sound waves enter the outer ear, the vibrations impact the ear drum and are transmitted to the middle and inner ear. In the middle ear three small bones called the malleus (or hammer), the incus (or anvil), and the stapes (or stirrup) amplify and transmit the vibrations generated by the sound to the inner ear. The inner ear contains a snail-like structure called the cochlea which is filled with fluid and lined with cells with very fine hairs. These microscopic hairs move with the vibrations and convert the sound waves into nerve impulses–the result is the sound we hear.
Exposure to loud noise with no noise barrier in place can destroy these hair cells and cause hearing loss!
What are the warning signs that your workplace may be too noisy?
Noise may be a problem in your workplace if:
- You hear ringing or humming in your ears when you leave work.
- You have to shout to be heard by a coworker an arm's length away.
- You experience temporary hearing loss when leaving work.
How loud is too loud?
Noise is measured in units of sound pressure levels called decibels using A-weighted sound levels (dBA). The A-weighted sound levels closely match the perception of loudness by the human ear. Decibels are measured on a logarithmic scale which means that a small change in the number of decibels results in a huge change in the amount of noise and the potential damage to a person’s hearing.
OSHA sets legal limits on noise exposure in the workplace. These limits are based on a worker’s time weighted average over an eight hour day. With noise, OSHA’s permissible exposure limit (PEL) is 90 decibels for all workers for an eight hour day. The OSHA standard uses a five decibels exchange rate. This means that when the noise level is increased by five decibels, the amount of time a person can be exposed to a certain noise level to receive the same dose is cut in half.
The National Institute for Occupational Safety and Health (NIOSH) has recommended that all worker exposures to noise should be controlled below a level equivalent to 85 decibels for eight hours to minimize occupational noise induced hearing loss. NIOSH has found that significant noise-induced hearing loss occurs at the exposure levels equivalent to the OSHA PEL based on updated information obtained from literature reviews. NIOSH also recommends a three decibel exchange rate so that every increase by three decibels doubles the amount of the noise and halves the recommended amount of exposure time.
Here’s an example: OSHA allows eight hours of exposure to 90 decibels, but only two hours of exposure to 100 decibel sound levels. NIOSH would recommend limiting the eight hour exposure to less than 85 dBA. At 100 decibels, NIOSH recommends less than 15 minutes of exposure per day.
In 1981, OSHA implemented new requirements to protect all workers in general industry (e.g. the manufacturing and the service sectors) for employers to implement a Hearing Conservation Program where workers are exposed to a time weighted average noise level of 85 decibels or higher over an eight hour work shift.
Hearing Conservation Programs require employers to measure noise levels, provide free annual hearing exams and free hearing protection, provide training, and conduct evaluations of the adequacy of noise deadening materials in use unless changes to tools, equipment and schedules are made so that they are less noisy and worker exposure to noise is less than the 85 decibels.