Noise is probably the most common occupational and environmental hazard. Workplace noise exposes 30 million Americans to potentially harmful levels. Environmental noise pollution has been doubling every decade. Outdoors, we have become inured to excessive and potentially damaging noise - power tools, firearms, recreation vehicles (motorcycles and snowmobiles), amplified sound (the ubiquitous boom boxes, enclosed and confined automobile music blaring at rock concert levels) - loud and severe enough to dislodge stubborn earwax and contribute to more than a third of 28 million Americans with some degree of hearing impairment.
And to add to the list of hazards, neither occupational nor environmental, but delivering a concentrate of noise right into the ear canal — music by MP3 or iPod, which at peak volume can deliver music at 110 to 120 dB, close to live-rock concert decibel-level.
Loud sound damages the tiny hair cells in the inner ear which are responsible for converting sound waves into electrical impulses that are sent to the brain. Hearing loss starts when 25 to 30% of the hair cells have been destroyed.
So, it won't hurt to
know your decibels.
Noise-induced hearing loss is an equation of volume and duration of sound exposure. Although the ear apparatus can recover from abuse, constant exposure to excessively loud sounds can eventually tire out and kill the hair cells with subsequent permanent hearing loss. The safe limit of noise-exposure has been set at 85 dB for 8 hours a day. And according to NIOSH (National Institute for Occupational Safety and Health) an increase of 3 dB cuts safe exposure time in half.
However, the numbers can be deceiving. For every five decibel increase, the intensity of sound doubles. A 20 dB sound is ten times louder than a 10 dB sound, and a 30 dB sound, 100 times louder than a 10 dB sound. Permanent damage can occur If your ears endure 85 dB for eight hours; at 95 dB, it takes only four hours. Also, a single gunshot, approximately 140 to 170 dB, has the same sound energy as 40 hours of 90 dB noise.
Sound pressure levels are normally measured in decibels (dB) and this logarithmic scale helps to manage the method of measuring. But it is not an intuitively easily understood scale for most people. A 3 dB increase or decrease in sound level equates to a doubling or halving of the sound level. A 10 dB increase or decrease represents a tenfold increase or decrease. But this does not readily translate into what we actually hear. For instance a 3 dB increase or decrease (doubling or halving) in the sound level of a radio playing or an aircraft flying overhead, would be virtually imperceptible (this is the threshold of being able to distinguish between sounds). A tenfold increase in sound level normally equates to a doubling of loudness and hence it doesn’t directly correspond to changes in dB sound levels.
Fortunately, decibel levels aren't additional. Simultaneous house chores with a vacuum cleaner (75 dB), dishwasher (75 dB), and washing machine (75 dB) do not add up to 225. A formula adjusts the concurrent exposure to a cumulative level of 81 dB.
Hearing loss is inevitable to some due to genetic predisposition or age-related hearing loss (presbycusis) that can affect a third of the population by age 65. Presbycusis is a consequence of many years of exposure to loud noise, smoking, and the ototoxic effect of more than a 130 medications, some of which are in common use.
Environmental noise pollution has been doubling every decade. Hearing loss is increasing in the United States. The number of Americans ages 3 and older with some form of hearing disorder has more than doubled since 1971, from 13.2 million to about 30 million today, and of these, a third from noise-induced hearing loss.
NIHL is 100 percent preventable. All individuals should understand the
hazards of noise and how to practice good hearing health in everyday
life. To protect your hearing:
As science wages its war
against deafness, noise is winning the battle. The generation of the pierced
and tattooed has found the ultimate isolationist tool — the iPod/MP3 — cranking out its shattering concentrates of music to the
auditory delight of the zombie'd youth keeping beat and dancing into the
valley of the walking deaf.
Additional Sources and Suggested Readings
Turn up your iPod, turn down your hearing / HEARING LOSS: NEWS AND REVIEWS
Noise-Induced Hearing Loss / National Institute on Deafness and Other Communication Disorders
Noise-Induced Hearing Loss / Peter Rabinowitz, MD, Yale University School of Medicine, New Haven, Connecticut / American Family Physician. May 1, 2000. Vol61, Number 9
The Portable Visual Encyclopedia / Running Press. Phila. PA
Hearing Loss: The invisible Disability / Jack Shohet MD and Thomas Bent MD. / Postgraduate Medicine. Sept 1998