More than 2,000 years ago, public spaces in Rome resounded with the din of horse hooves and the clatter of iron chariot wheels on cobblestone streets. Because this racket interrupted the sleep of the royal family, a legend claims that Emperor Julius Caesar proposed a city-wide ban on chariot traffic at night. This might be the earliest recorded example of a noise abatement program.
Many of us are occasionally bothered by sounds such as the neighbor’s dog barking, jackhammers chiseling pavement across the street or a car stereo system cranked up so loud that our bodies vibrate as the vehicle passes. These sounds annoy us primarily because someone or something else is making the noise and imposing it on us. We especially loathe such impositions that are outside of our control. However bothersome such sounds might be, unless we are riding inside the “boom car” or operating the jackhammer, physical distance from the source usually precludes physiological damage to our ears. By contrast, loud sounds in close proximity damage auditory structures and contribute to noise-induced hearing loss (NIHL).
In December 1960, New York otolaryngologist Dr. Samuel Rosen led an expedition of health professionals to assess the Mabaan people in southeastern Sudan (see Figure 1). According to Rosen, the Mabaans were a pre-Nilotic, pagan, primitive, tribal people whose state of cultural development was the late Stone Age. “They are a peaceful and quiet people, about 20,000 of them, living in small huts with straw-thatched roofs and bamboo sides . . . they have no guns, but hunt and fish with spears. They do not use drums in their dance and song, but pluck a five-string lyre and beat a log with a stick.” Dr. Rosen and his colleagues administered hearing tests to 541 Mabaans ranging in age from 10 to over 90 years. In our society, we would expect to see a distribution of hearing test results for different age groups as shown in Figure 2.
Mabaan audiograms were similar to those for young people (age 0-20 years) from industrialized nations. However, for every subsequent decade of life, Mabaan hearing was significantly better than that of people in modern societies. In fact, auditory thresholds for 70- to 80-year-old Mabaans were comparable to those recorded from 20- to 30-year-old individuals from western civilizations. Rosen wrote, “It is tempting to speculate on the reasons for the striking differences. The Mabaan environment is indeed dramatically quieter at almost all times than environments of populations sampled in our culture . . . except for occasional transients, usually the fleeting noises of domestic animals, few other sounds were sufficiently intense to yield a reading on the sound level meter (which could read as low as 34 decibels (dB). [In their 1960 report on hearing loss], Glorig and Nixon make a case for noise as the critical factor in the differences in hearing with aging in various populations. The results of the present study appear to support this view.”
Follow-up studies showed that Mabaan people who moved to urban areas to live and work exhibited more hearing loss, higher blood pressure and more cardiovascular disease than their counterparts who remained in the countryside.
Between the late Stone Age and modern times, human society has become increasingly noisy. Also, the association between loud noise exposure and hearing loss has been apparent for centuries. In 1591, Italian artist Cherubino Alberti noticed many “cases of acquired deafness caused by intense noise such as cannonading and thunder.” Italian physician Bernardino Ramazzini reported cases of Coppersmith’s Deafness in 1713; Englishman Thomas Dudley Fosbroke coined the term Blacksmith’s Deafness in 1831 to characterize hearing loss associated with the profession; and in 1882, otolaryngologist E.E. Holt described Boiler-maker’s Deafness and used a ticking pocket watch to detect high-frequency hearing loss.
Modern audiometry allows us to document the clear correlation between exposure to excessively loud sounds and NIHL. For example, the audiogram in Figure 3 shows a “noise notch” in the left ear of the person tested.
What is a likely cause of this configuration of hearing loss? An experienced audiologist or otolaryngologist would ask the patient two questions: “Have you ever shot guns?” and “Are you right-handed?” Right-handed people who shoot rifles or shotguns often exhibit more hearing loss in the left ear because their right ear is protected by the gunstock and the shooter’s right shoulder. Gunfire is so loud (140-170 dB, depending on the type of weapon) that it can cause immediate damage to auditory structures and permanent hearing loss, even if a person fires a gun only once without wearing hearing protective devices (earplugs or ear muffs). Millions of people are exposed to and injured by excessive sound levels during recreational activities. However, many people also suffer from NIHL related to their occupation.
According to the National Institute for Occupational Safety and Health (NIOSH), approximately 30 million American workers are exposed to hazardous noise levels on the job. NIOSH explains that NIHL is the most common occupational disease and the second most self-reported occupational illness or injury.
How loud is too loud for the human auditory system? As seen in Table 1, sounds 80 dB or softer, such as normal conversations, music, television or radio programs at reasonable volumes, are considered safe and can be listened to for extended periods of time. Sounds louder than 80 dB have the potential to damage hearing over time.
Table 1 utilizes a 3-dB exchange rate: for every 3-dB increase in sound intensity, the duration of safe exposure time is cut in half. Unfortunately, the Occupational Safety and Health Administration (OSHA) uses a 5-dB exchange rate and a 90-dB permissible exposure limit in its regulations of occupational noise for American workers. OSHA’s regulation (29 CFR Section 1910.95) for occupational noise exposure was published in the Federal Register in 1983 and is still in force today. The regulation gave rise to what OSHA calls “Permissible Noise Exposures” (shown in Table 2).
By using a 90-dB permissible exposure limit and a 5-dB exchange rate, OSHA regulations permit American workers to be exposed to hazardous levels of sound for longer periods of time than the ones recommended by most experts in hearing across the country.
If this is common knowledge, why haven’t stricter regulations been put into effect? If the 85-dB permissible exposure limit and 3-dB exchange rate (85/3) were adopted, industries would need to spend more money to meet the standards. Section 1910.95(b)(1) of OSHA regulations states that when employees are subjected to sound levels exceeding those listed in Table 2, “feasible administrative or engineering controls shall be utilized.” If such controls fail to reduce sound levels within the levels of Table 2, “personal protective equipment shall be provided and used to reduce sound levels within the levels of the table.” Such equipment would cut into corporate profits and therefore businesses have a vested interest in keeping OSHA noise regulations just as they are.
The more conservative criteria of 85/3 have already been implemented by the U. S. Department of Defense and are recommended by organizations such as NIOSH, National Hearing Conservation Association, American Industrial Hygiene Association, International Safety Equipment Association and American Conference of Governmental Industrial Hygienists. China, Mexico, Canada, Australia, Argentina, Venezuela, Chile and most nations in Western Europe have more progressive hearing loss prevention policies than the United States. While we wait and wait for OSHA to adopt new standards, more American workers are suffering damage to their hearing than should be allowed.
In addition to problems associated with less-than-conservative OSHA standards, hearing loss prevention efforts are also plagued by worker noncompliance. A fantastic array of hearing protective devices is now available, including comfortable earplugs, ear muffs, headsets and ear pieces that facilitate two-way communication. However, too many workers and military personnel choose not to use such devices at all, use them intermittently or do not use them properly. Because NIHL is often a gradual process that progresses over years and decades, people tend to take hearing for granted until their own hearing loss becomes so severe that it interferes with communication.
Costs for remediation, rehabilitation and lost productivity for people who experience NIHL and tinnitus are substantial. Afflicted individuals often experience decreased enjoyment and quality of life. Every person who can be spared the debilitating consequences of NIHL (including communication difficulties, social isolation, depression and tinnitus) is worth the effort.
“Effort” is a key word in hearing conservation. The goal of hearing loss prevention programs is to motivate individuals to implement strategies to reduce the risk and prevalence of NIHL. This requires effort by all parties involved. Wouldn’t it be easier to take a pill to prevent hearing loss? Magnesium supplements, vitamins A, C and E, N-acetylcysteine, a compound called ebselen and several other substances all reportedly reduce the amount of hearing loss or severity of damage to auditory structures following acute noise exposure. While these compounds and supplements might eventually have some practical utility, I believe that an ounce of hearing loss prevention education is worth a pound of pills.
A good place to start hearing loss prevention efforts is to teach children these three concepts:
• the sources of dangerous sounds
• the consequences of exposure to dangerous sounds
• how to protect oneself from dangerous sounds.
The last point is easy to address: turn down the volume of personal stereo systems, move away from the source of loud sounds whenever possible and wear earplugs or ear muffs when you are exposed to excessively loud sounds such as gas-powered lawn mowers, power tools, gunfire or music.
“Establishing healthy behaviors during childhood is easier and more effective than trying to change unhealthy behaviors during adulthood,” states the Web site for Centers for Disease Control and Prevention’s Healthy Youth! program. If elementary school children are educated about NIHL and hearing loss prevention, they will be more likely to protect their hearing in future occupational and recreational settings.
Figure 4. Poster from Howard Leight Industries
Robert L. Folmer, Ph.D., is program manager for the Hearing Loss Prevention
Initiative at the National Center for Rehabilitative Auditory Research (NCRAR) within the Veteran’s Administration Medical Center in Portland, Ore. He is also an associate professor of Otolaryngology at Oregon Health & Science University.
