Hearing loss is a gradual and irreversible process; without regular testing, few workers will realize that they are losing their hearing until it is too late. Therefore, prevention measures must be taken by employers and workers to ensure the protection of workers' hearing since working near noisy equipment may be enough to damage hearing.
How do we hear?
Hearing is a series of events in which the ear converts sound waves into electrical signals that are sent to the brain and interpreted as sound. The ear has three main parts: the outer, middle, and inner ear. Sound waves enter through the outer ear and reach the middle ear where they cause the eardrum to vibrate. The vibrations are transmitted through three tiny bones in the middle ear, called the ossicles. These three bones are named the malleus, incus, and stapes (and are also known as the hammer, anvil, and stirrup). The eardrum and ossicles amplify the vibrations and carry them to the inner ear. The stirrup transmits the amplified vibrations through the oval window and into the fluid that fills the inner ear. The vibrations move through fluid in the snail-shaped hearing part of the inner ear (cochlea) that contains the hair cells. The fluid in the cochlea moves the top portion of the hair cells, called the hair bundle, which initiates the changes that lead to the production of nerve impulses. These nerve impulses are carried to the brain, where they are interpreted as sound. Different sounds move the hair bundles in different ways, thus allowing the brain to distinguish one sound from another, such as vowels from consonants. Continuous exposure to loud noise can damage the structure of the hair cells, resulting in hearing loss and tinnitus (ringing in the ears).
NIHL can be caused by a one-time exposure to loud sound as well as by repeated exposure to sounds at various loudness levels over an extended period of time. The loudness of sound is measured in units called decibels. For example, normal conversation is approximately 60 decibels, the humming of a refrigerator is 40 decibels, and heavy city traffic noise can be 85 decibels. Examples of sources of loud noises that cause NIHL are motorcycles, firecrackers, and firearms, which emit sounds over 120 decibels. Sounds of less than 80 decibels, even after long exposure, are unlikely to cause hearing loss.
People with hearing loss often become socially isolated because they cannot communicate easily with others. They also may not be able to hear warning signals, and so may have an injury.
For more information, please see:
NIOSH Noise Topics
Noise and Hearing Damage in Construction Apprentices