Noise-induced Hearing Loss

Noise-Induced Hearing Loss: What it is and what it may mean to you

A preliminary report

February 16, 1994

 

Though written especially for Hare Krishna devotees, this report–a nontechnical discussion of noise-induced hearing loss–should prove relevant for anyone in a noisy world.

The report discusses what noise-induced hearing loss is, how it develops, and what to do about it.

 

Last month an audiologist confirmed to me something I suspected: I have partially lost my hearing.

One may lose one’s hearing for many reasons—because of disease, or old age, or a blow to the head, or close exposure to the sound of blasts or gunshots. But the test of my hearing showed the typical signature of another kind of problem: hearing loss from prolonged exposure to noise.

Well, it doesn’t have to be noise, by which I mean disturbing or unpleasant sounds. One can also lose one’s hearing because of sounds one might find pleasant—like the sound of rock music, or classical. Or drums and karatals [hand cymbals].

Loss of hearing—for a while and for the rest of your life

Noise-induced hearing loss has two components: temporary and permanent. If you’ve ever attended a rock concert, for example, you may be familiar with temporary hearing loss. After the concert you may have found your ears ringing, and ordinary sounds may have seemed muffled. The ringing is a response from your assaulted auditory nerves. And that “muffled” effect comes from what’s called a “temporary threshold shift.” That is, after the blasting music, other sounds now need to be louder before you can hear them.

In temporary hearing loss, after a few minutes or or a few hours the ringing stops, and your hearing goes back to normal. But when loud sounds fall upon your ears repeatedly over a prolonged time, for months and years, the threshold shift becomes permanent. Your hearing loss is then irreversible.

The site of the damage responsible for this loss is the cochlea, a snail-shaped chamber within the inner ear. The cochlea is home to the 20,000 to 30,000 minute hair cells that transmit sound to the auditory nerve. Prolonged and excessive exposure to noise injures and finally destroys those cells. Once destroyed, the cells never come back.

How loud is the sound?

The loudness of sounds is measured in units called decibels, just as temperature is measured in degrees. Note, however, that, unlike degrees, decibels are not absolute units. Measurements in decibels are logarithmic, not linear. Imagine, if you will, a thermometer in which going up from 70 degrees to 73 means getting twice as hot, from 70 to 76 means 4 times hotter, and from 70 to 79 means 8 times hotter. That’s the idea. Every time the sound level goes up 3 decibels, the sound gets twice as loud.

How loud are the sounds we’re accustomed to hearing? Here’s a list that will give you a basic idea:

 

0 dB: threshold of hearing in youths

10 dB: anechoic room

30 dB: quiet library

45 dB: average residence

55 dB: normal conversation

60 dB: large store

70 dB: vacuum cleaner (10 feet away), freight train (100 feet away)

75 dB: average factory

80 dB: alarm clock, normal traffic, loud orchestra, pneumatic drill (from 50 feet)

85 dB: START OF UNSAFE LEVELS

90 dB: lawn mower, motorcycle, city traffic, boiler room, printing press room, subway train (from 20 feet)

100 dB: riveting machine

110 dB: thunder, pile driver, amplified rock music

125 dB: jet takeoff (from 200 feet away)

130 dB: pain threshold

The loudness of a sound depends, of course, on how far you are from its source, how clear the path between the sound and you, and what happens to the sound along the way. For example, a sound made outdoors might be moderately loud, but the same sound made in a small closed room with smooth walls will ricochet many times over, so its effect will be more intense.

How loud is an ISKCON kirtana ["ISKCON" is an acronym for the International Society for Krishna Consciousness, and "kirtana" means a chanting session]? I can’t say for everywhere. But according to a series of readings with a sound-level meter, here’s what it is in the temple room in Alachua. A typical guru-puja kirtana, with 3 drums, 2 or 3 sets of karatals, 2 moderate-sized “whompers” [large cymbals], and the usual amplification comes to around 100 decibels, with a sustained crescendo of 106 to 110.

Does that level of sound present a danger to hearing? Read on.

 

It happens without your knowing

The pitch, or frequency, of sounds is measured in units called Hertz (Hz). Young children may hear sounds as low as 16 Hz (lower in pitch than the lowest note on a piano) and as high as 20,000 (well above the highest note on a piccolo). As we grow older, the upper limit comes down, so that many adults can’t hear sounds above 12,000 Hz. The range of frequencies for speech extends from about 200 Hz to about 6,000. Music, of course, extends higher.

What happens in noise-induced hearing loss is that you start to lose your high frequencies. Typically, the tones around 4,000 Hz are the first to go. You may still hear those tones, but only when they’re louder than before. Young, healthy ears pick up sounds as soft as 10 or 20 decibels. With noise-induced hearing loss, you may not hear those sounds unless they’re many times louder, say 50 decibels.

The next tones to go might be in the range of 6,000 and 8,000 Hertz, as the hairs in your inner ear that respond to those frequencies are gradually damaged and then destroyed.

At this stage, you’re unlikely to notice what’s happening. The main sounds you’re conscious of are the sounds of speech, which mostly occupy the lower frequencies, 2,000 Hertz and below. Some consonants—like s, f, ,t and z—do extend into the higher frequencies, but even when you fail to hear them, your mind automatically uses the context given by the other letters to supply the sounds you’ve missed. So hearing seems to go on as normal. You’re losing your hearing, and you don’t even know it.

Noise-induced hearing loss progresses very slowly. It usually takes many months, and often years. Along the way, you feel no pain, see no blood or bruises. So you don’t realize what’s happening.

Next, however, the losses in the higher frequencies may become greater, and the lower tones may also start to give way. Now you start having trouble hearing speech. Actually, you can still hear it, but you start having trouble *distinguishing* what’s being said.

Now you may start to complain about your hearing. But by now the damage done is severe, irreversible, and perhaps even seriously handicapping.

Another problem I should mention (I mentioned it briefly before) is what’s technically called tinnitus (from a Latin word meaning “to ring”). This is a ringing, buzzing, whistling, or other such sound in the ear. Though disturbing, it’s generally temporary. But when damage in the inner ear has brought about a permanent loss in hearing, a ringing tinnitus may go on for many years.

Tinnitus, says one authority, does not commonly occur from exposure to everyday occupational noise. But “it does occur in employees who are exposed to very high-pitched intense noise, such as pounding of metal upon metal in foundries.” 1

Like noise-induced hearing loss itself, tinnitus has no known cure. You just have to learn to live with it.

How much can you take?

It’s generally accepted that when a sound is excessively loud, the longer you’re exposed to it the more you put your hearing at risk. What’s a “safe dose” of loud sound?

This is a question to which much research and discussion has been devoted. The research has evolved, in particular, from the need to protect people from excessive noise in the workplace, especially the military and industrial workplace.

In America, the Occupational Safety and Health Administration (OSHA) has set standards limiting the time to which employers can let their workers be exposed to various levels of sound. Here are the standards:

 

Sound level (dB) Hours per days
90 8
92 6
95 4
97 3
100 2
102 1-1/2
105 1
110 1/2
115 1/4 or less

 

 

These numbers, however, represent legal standards, not medical or scientific ones. They belong to rules meant to help protect the hearing of workers (and protect employers in lawsuits brought by workers with hearing impaired).

Comments B. Adam Sagan, a lawyer with graduate degrees in audiology and speech pathology, “Both medical experts and speech scientists [agree] that the standards issued by OSHA are more a result of political compromise than scientific validity.”2

This is underscored by Donald C. Gasaway, one of America’s foremost experts on hearing loss and hearing conservation. “Many people [have] suffered a noise-induced loss because they were led to believe that higher levels of noise could be tolerated if the duration of exposure was less than some ‘magic’ number.. . . Such belief comes from what, in my opinion, is the misapplication of auditory risk criteria. If a given assessment states that 100 dB. . . is associated with a ‘dose’ of 30 minutes per day, there may be a general acceptance that the ‘risk’ is nullified if the duration is one-half of the ‘allowed’ dose, such as 15 minutes. I consider adoption of this belief a primary contributor to noise-induced losses. I have learned to respect seriously the danger of such high-level exposures, even for 2 minutes. In my opinion, those who provide guidance concerning such exposures should adopt a more cautious approach.”3

As reported in Health News, published by the University of Toronto, “At a level of 110 dB, even five minutes of unremitting exposure can lead to some hearing loss.”4

Health News summarizes things this way: “To determine whether your environment is loud enough to harm the ears, check whether you have to shout to make yourself heard or if, when you leave a noisy environment, sound seems muffled. If yes, the noise level is too high and already injuring your ears. “While entirely preventable, noise-induced hearing loss is also entirely incurable. According to the U.S. National Institutes of Health, millions of North Americans are at risk of hearing loss from noisy work situations, especially farmers, truck drivers, miners, industrial and construction workers, policemen and musicians (playing in the orchestra or rock band can be a very noisy job). “The currently suggested level at which hearing protection should begin on a voluntary basis (no laws about it) is 85 dB. According to ear specialists it should be mandatory at 90 dB. People with jobs that expose them to noise over the 85-decibel level for a prolonged time should wear personal hearing protectors (earplugs or earmuffs) and turn the volume down during recreational activities. Remember that levels from rock bands and personal stereos may far exceed the danger limit!”5

What this means to ISKCON

How all this pertains to ISKCON should by now be reasonably obvious. As part of our prescribed routine program, we expose ourselves, and those for whom we are responsible, to levels of sound well within the range where loss of hearing should be a matter of concern. Drums and karatals are loud to begin with. And lately karatals of giant size have come to be something of a fashion. We play our instruments indoors, in what are often small rooms with low ceilings and smooth walls and floors. And then we electronically amplify the sound.

Beyond this, devotees generally have little or no education about what the physical effects of loud sound on the ears can be. And so during kirtana we turn up the volume to maximum. We even see devotees playfully using karatalas as if to box the ears of other devotees. Within my own experience, last year one senior devotee came up close to me during kirtana as if to whisper something in my ear, and then shouted at the top of his lungs, “GOVINDA!” We sometimes have ill-informed ideas about how to express our ecstasy.6

We are responsible, of course, for large numbers of people, including children. We want them to be fit and healthy for devotional service. And we are ethically accountable for their welfare.

Apart from that, we can suppose that people more cautiously protective of their hearing may be hesitant to join in the Hare Krishna movement as word gets around that a disproportionate number of its members eventually need hearing aids and acoustic earmuffs.7

Stopping it from happening

Noise-induced hearing loss, though permanent and irreversible, is largely preventable. The way to prevent it is through what is known as a Hearing Conservation Program. Such programs have been in place in all branches of the U.S. military since the 1950’s, and U.S. law has made them mandatory in high-noise industrial environments since 1971. Such a program is appropriate—and important—for any organization that expects its members to be regularly exposed to high levels of sound.

An effective Hearing Conservation Program generally has seven parts:8 (1) measuring levels of exposure, (2) controlling the level of sound, (3) testing the hearing of your people, (4) seeing to the use of ear protectors, (5) educating and motivating your people, (6) keeping records, and (7) seeing how well your program is doing.

Let me briefly explain each one.

1. Measuring the level of exposure.

How loud is the sound? Does it present a problem or not? There are standard equipment and procedures that will tell you. (It’s not expensive.)9

2. Controlling the level of sound.

Once you know how loud your sound is, if it’s too high you can work to bring it down. In a factory this might mean using quieter machines or sealing off areas that are noisy. Controlling sound in ISKCON centers might involve, for example, turning down amplifiers, placing limits on the use of certain instruments, and using sound-absorbing materials for softer acoustics in temple rooms.

In these efforts the first step—obvious but easily overlooked—is for the person or governing body in charge to take them seriously.

3. Testing the hearing of your people.

If your sound is at safe levels, fine. If not, your people should have regular, periodical hearing tests.

Hearing tests are brief, standard medical procedures, performed with a tone generator and earphones, to tell you what’s happening to a person’s hearing. They are usually performed by a mobile testing unit or at a local hearing clinic, though they may also be done in-house by a person properly trained.10

Since noise does most of its damage before a person even notices that his hearing is going bad, hearing tests are the only sure way to detect trouble in time to prevent it.

Hearing tests also provide the way for you to tell how well your hearing-conservation program is working.

4. Seeing to the use of ear protectors.

If you can’t cut down the sound, people may need to directly protect their ears.

A wide selection of protective devices is available—various kinds of ear plugs, ear putty, and so on. But they only work properly when properly chosen, fitted, and used. People who need them should be encouraged to use them, and shown how to use them properly.

For people whose hearing has already been affected, using hearing protectors—or staying away from loud sound altogether—is the only way to keep their ears from getting worse.

5. Educating and motivating your people.

In a movement such as ours, I hope it’s needless to explain why people don’t deserve to be left ignorant.

Of course, we’re mainly concerned about spiritual understanding. But since our process of spiritual enlightenment depends, most of all, upon hearing, it follows that devotees ought to safeguard the proper functioning of their ears.

This, too, requires proper education and encouragement.

6. Keeping records

Properly kept records allow you to keep track of what’s going on with your program. Also—of crucial concern—they’re essential for keeping track of the aural health of individual devotees.

7. Seeing how well your program is doing.

Periodically reevaluating your program helps you see how well it’s working, alerts you to problems, and helps you see any changes you should make.

Closing remarks

There. Now, I hope, I’ve alerted you and somewhat informed you. Take it lightly if you will. But be warned: If you ignore all this, soon you and other devotees may wind up expanding the ocean of Krishna’s glories by often repeating a new mantra: “Say that again?”

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ENDNOTES

1. Sataloff, Joseph and Michael, Paul, Hearing Conservation (Springfield, Illinois: Charles C. Thomas, 1973), pg. 83.

2. B. Adam Sagan, “Occupationally Induced Hearing Loss: A Real World Perspective,” The Legal Intelligencer, June 1, 1993.

3. Gasaway, Donald C., 1985, Hearing Conservation: A Practical Manual and Guide, Englewood Cliffs, N.J.: Prentice-Hall, p. 67-68.

4. Health News, University of Toronto, August 1993, p. 5.

5. Ibid.

6. My audiologist, a pious Hindu lady in South Africa, advised me that we ought to be concerned about sound levels higher than 80 decibels. Maybe to pray to Satan and block out your mind, you might need 100 decibels, she remarked. But for praying to God, 80 decibels ought to be enough.

7. To those who’d say that limitless volume is ok because the holy name is transcendental, the response is simple: Your hearing loss will also be transcendental.

8. Suter, Alice H. and Franks, John R. (ed), A Practical Guide to Effective Hearing Conservation Programs in the Workplace, U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Biomedical and Behavioral Science, Physical Agents Effects Branch, September 1990.

9. Sound-level meters are availabale from Radio Shack for $31.99. Catalog number 33-2050.

10. What does it cost? In an article published in 1987, the principal consultant for the Engineering Department at E.I. du Pont said that taking part in a hearing-conservation program costs “between $20 (Du Pont’s estimate) and OSHA’s estimated $41 per employee per year.” Presumably, that’s for the whole cost of the program. (Terrence A. Dear, “Noise Criteria Regarding Risk and Prevention of Hearing Injury in Industry,” in Sataloff, Robert Thayer and Joseph, 1985, Occupational Hearing Loss, New York: Marcel Dekker, Inc., p. 498.

A glance at the Gainesville Yellow Pages shows several hearing-aid retailers that provide free hearing tests. On the phone, one such company told us they recommend that you come in for a free test once every year.

 

Comments

  1. babhru says

    The VA hospital in Gainesville just fixed me up with a device that helps those afflicted with tinnitus deal with the problem. It’s a portable electronic device. The site for the company that makes it is http://www.neuromonics.com. It’s available through audiology clinics, it’s not available everywhere, and I don’t know how much it would cost. (The earphones alone are $160 Bang-Olufsens.) But it may be worth checking out.

  2. jswami says

    Interested in hearing protectors that bring down the volume but preserve the natural quality of the sound?

    You might like to try the high-fidelity earplugs–ER-20’s–made by Etymotic Research. (The company is now branding them as “ETY-Plugs.”)

    They cost about $12, last indefinitely, and don’t need to be rolled like foam plugs. And they make the sound quieter without making you feel like you’re under water.

    You can order them online from The Ear Plug Store.

    In the UK the Etymotic earplugs are marketed as Elacin ER-20’s. You can get them online from Audio Relief.

    More widely available in Europe are similar earplugs from the Dutch company Alpine. You can find these in the UK at, for example, Audio Relief, Enhanced Listening, Sensorcom.com, or Earplugshop.com.