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Written by Robert E. Sheriff, MS, CIH, CSP, President and Henry P. Shotwell, Ph.D., CIH, Vice-President
November 7, 2018
Noise can be described as loud, unwanted sound. Sound is produced by the rapid compression and decompression of air. When you clap your hands, you are producing a sound by compressing and decompressing the air between the palms of your hands. Clapping faster produces a higher frequency or pitch of the sound. When sound waves enter the ear canal, they hit against the eardrum, a flexible piece of tissue that moves back and forth as the sound pressure builds up and falls off. Attached to the eardrum are three small, connected bones (the middle ear) which transmit movements of the ear drum to the inner ear. Inside the inner ear is a fluid that sloshes back and forth in the rhythm with the ear drum and middle ear. Special nerve cells leading to the brain have hair-like structures floating in the inner ear fluid. Movement of the eardrum, middle ear and inner ear fluid cause these “hairs” to sway back and forth. When they move, nerve impulses are sent to the brain where they are interpreted as sound soft or loud, pleasant or unpleasant, high pitched or low pitched.
When the sound is loud, the sound energy hitting the eardrum is high. This causes the hair cells to bend a lot, sending a more powerful impulse to the brain. If the sound is high pitched, the hair cells have very little time between sound waves to recover their normal, upright position.
When sound is both loud and high pitched, these inner ear nerve cells never get the chance to recover, and they die. If enough of them die, hearing loss occurs. Once these cells die, they never regenerate; “noise induced hearing loss” is permanent and irreversible.
Noise that results in damage to this hearing mechanism can come from any source—work, home, entertainment. Loud music from a live performance or a set of earphones, if loud and repeated, can have the same detrimental effect as a noisy machine at work. Noise occurs in non-work situations as well, such as concerts, leaf blowers, racing or woodworking.
OSHA has set a maximum 8-hour exposure to noise in the workplace at 90 decibels at 1,000 cycles per second (Hertz, Hz). Because this is not a particularly protective level, they instituted an Action Level (AL) of 85 decibels (dBA). If you have a workplace in which 8-hour time weighted average exposures are at or above 85 dBA, but less than 90 dBA, the regulations require a hearing conservation program, which includes training, hearing protective devices, baseline and annual hearing tests and feasible engineering controls to reduce the noise levels to a point below 85 dBA.
Communities often have noise standards as well, but these are usually set for comfort, or disturbance. Generally they are set in time frames: 7 pm-7 am – max 65 dB-A – 7 am-7 pm – max 80 dB-A.
The community noise levels can be measured with a hand-held or tri-pod mounted sound level meter (SLM) or an octive band analyzer.
Our primary service areas for Noise Consulting and Testing/Sampling are: NJ, NY, NYC, PA, CT, DE, (Boston) MA, RI, Wash DC, WI, MD, MI, (Chicago) IL, VA, IN, (Atlanta) GA, AL, NC, SC, TN, (Dallas, Ft Worth) TX, OK, DC, AR, we can service most other areas of the U.S. but with some added travel charges.