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.

Decibels (dB) are measurements of noise. The decibel (dB) is the unit used for the loudness of a sound, or its sound pressure.

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.

Recommendations, Precautions, Prevention
• Avoid noise that is too loud, too close, and for long periods of time; those above 85 decibels can cause damage.
• Noise-induced hearing loss is 100 percent preventable.
• Ear protection can reduce exposure to unhealthy decibels of sound and helps prevent noise-induced hearing loss. Earmuffs, custom-fitted plugs, and disposable earplugs can provide 20 to 40 dB of sound attenuation and should be used especially by those recurrently exposed to high noise levels.
• iPod or other personal music player should be used at 60% of the peak volume and for no longer than 60 minutes a day, with lower volumes for longer listening time.
• Use of noise-canceling headphones or headphones that block competing background sound will help down-regulate the volume.
• IPod has free software that sets maximum volume on players.
• Earbuds that concentrate and intensify the sound signals have a greater potential of hearing loss. Because it fits snugly and deeply in the ear canal, the volume of air and the distance of music source to eardrum is greatly reduced, doubling the relative level of noise exposure and reduces the amount of time for safe-listening. Some experts suggest limiting earbud-delivered music to 30 minutes a day.
• Use earplugs or ear muffs for prolonged exposure to dangerous levels of noise.

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:
• Know which noises can cause damage (those at or above 85 decibels).
• Wear earplugs or other hearing protective devices when involved in a loud activity (special earplugs and earmuffs are available at hardware and sporting goods stores).
• Be alert to hazardous noise in the environment.
• Protect the ears of children who are too young to protect their own.
• Make family, friends, and colleagues aware of the hazards of noise.
•If you suspect hearing loss, have a medical examination by an otolaryngologist (a physician who specializes in diseases of the ears, nose, throat, head, and neck) and a hearing test by an audiologist (a health professional trained to measure and help individuals deal with hearing loss).

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.