Noise & Hearing - The Facts
Including a Special Section on "Hearing Protection - Sunglasses for the Ears" with excerpts taken from The EARLog Series by Elliott Berger
Hearing Rehabilitation Quarterly - Special Edition (2001)
Noise Threatens Hearing
Exposure to loud noise is one of the leading causes of hearing loss in the 28 million people with impaired hearing in the United States. Firefighters, police officers, factory workers, farmers, construction workers, military personnel, heavy industry workers, musicians and entertainment industry professionals all work in environments that pose noise risks. Even those sounds that we choose - those sounds to which we're exposed while we're enjoying recreational activities - can be dangerous to our hearing. Noise levels at video arcades, live music concerts, and sporting events, to name just a few, can pose a risk to hearing.
How Loud is Too Loud?
To know if a sound is loud enough to cause damage to your ears, it is important to know both the level of intensity and the length of exposure to the sound. The unit used to measure environmental sound intensity is the decibel (dBA). Zero decibels is approximately the softest sound the healthy human ear can hear. The scale increases logarithmically; that is, the level of perceived loudness doubles every 10 decibels. Experts agree that continued exposure to noise above 85 dBA, over time, will eventually harm hearing. In general, the louder the sound, the less time required before hearing will be affected. A rule of thumb to follow: If you have to shout in order to be heard three feet away by a person with normal hearing, then regular exposure to the noise will be potentially damaging to your hearing.
Noise-Induced Hearing Loss - How the Damage Occurs
Loud noise assaults the delicate hair cells of the inner ear. Noise-induced hearing loss typically occurs gradually and without pain. After exposure to loud noise, a person may experience ringing in the ears or difficulty hearing. This is called a "temporary threshold shift." After a few hours (or in some cases, a few days), this temporary shift in hearing returns to normal. With repeated exposure, however, this temporary shift in hearing can become permanent. Once permanent hearing damage has occurred, it is not possible to restore hearing.
Pay Attention to the Warning Signs
Noise-induced hearing loss is cumulative across the life span. Often, by the time a person realizes that there is hearing loss, it is too late. But there are certain early warning signs to suggest that there may be a problem. If you experience any of the following early warning signs, have your hearing tested by a licensed audiologist, or have your ears examined by an ear doctor.
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A ringing or buzzing (tinnitus) in the ears immediately after exposure to noise.
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A slight muffling of sounds after exposure making it difficult to understand people when you leave a noisy area.
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Difficulty understanding speech; that is, you can hear all the words, but you can't understand all of them.
Protect Your Hearing
To avoid noise-induced hearing loss, pay attention to the noises around you and turn down the volume whenever possible. Avoid or limit time spent in noisy sports events, rock concerts and night clubs. Wear adequate hearing protection, such as foam earplugs or earmuffs, when you must be in a noisy environment or when using loud equipment.
Questions and Answers about Hearing Protection
People often avoid using hearing protection devices (HPDs) because of common misconceptions associated with the hearing protection. There are numerous options available in hearing protection that are easy to use and can help avoid a lifetime hearing disability. The following material is excerpted from The EARlog Series by Elliot H. Berger, Senior Scientist, Auditory Research, E-A-R-. The entire series of 21 articles can be found at www.e-a-r.com/html/indeustrial/earlog.htm
Excuse: I don't need hearing protection; I am used to the noise.
Response: Ears do not get used to noise - they "get deaf" (and unfortunately a deafened ear may often seem to get used to the noise). Repeated exposure to noise does not toughen ears nor does having an existing noise induced hearing loss prevent you from losing the hearing you have left. Although individual susceptibility to hearing loss from noise exposure varies widely, there are currently no standardized tests that can detect the more noise sensitive members of the population.
Question: I've already lost some or most of my hearing. Why should I have to wear hearing protection?
Response: The existence of a noise induced hearing loss does not protect one from further loss of hearing due to noise exposure. Initially hearing is damaged in the higher frequencies and as the unprotected exposures continue, this damage spreads to the lower frequencies, eventually affecting those essential to the understanding of speech (500 Hz to approximately 3000 Hz).
Although HPDs cannot restore a noise induced hearing loss, which by its nature is permanent and irreversible, they should prevent additional losses from being incurred.
Complaint: Hearing protectors are uncomfortable.
Response: HPDs are often uncomfortable initially, but hearing loss due to noise exposure is "uncomfortable" permanently. Like a new pair of shoes or glasses, hearing protectors do require a reasonable period of adjustment. Since not all hearing protectors adapt equally well to all head shapes and earcanals, it is important to give the employee the final choice in what he or she will wear. If after a couple of weeks of daily use the employee is still experiencing difficulties or discomfort, the protector should be resized and/or refitted, or another hearing protector should be issued.
Complaint: I can't hear my fellow workers if I wear hearing protectors.
Response: When the ear is bombarded with high level sound, it overloads and distorts, reducing its ability to accurately discriminate different sounds. Wearing HPDs reduces the overall sound levels so that the ear can operate more efficiently. The effect is similar to the improved vision that sunglasses provide in very bright, high-glare conditions.
For those with normal hearing, HPDs will usually provide improved communications when sound levels are greater than approximately 85 dBA. For moderate to severely hearing impaired individuals, the situation is more complicated; for them, hearing protectors may not provide a communications benefit and actually be a liability. But, if these individuals do not protect their hearing, they may suffer additional impairment, and then they will have even greater difficulty communicating regardless of noise level.
Question: Do earmuffs block out noise better than earplugs?
Response: No. The misconception that earmuffs are better than earplugs at reducing noise is partly due to the "bigger is better" school of thought. Actually, whether or not an earmuff or an earplug is better is dependent upon the device and user in question.
Question: Can earplugs cause ear infection?
Response: Based on our experience during the past decade, and information gleaned from consultation with experts in the field of otology and audiology, as well as data from an ongoing survey of U.S. industries, it appears that the likelihood of earplugs causing outer ear infections (otitis externa) is minimal. Although it would seem that placing a dirty or gritty foreign object in the earcanal could easily lead to irritation or infection, the data from existing HCPs [Hearing Conservation Programs} seem to indicate that the external ear is fairly resistant to such abuse. Nevertheless, cleanliness should be stressed and certain individuals, such as diabetics and those who are prone to infection, should be more carefully monitored.
Question: Can hearing protectors cause headaches, nosebleed, ulcers, insomnia or eyestrain?
Response: Headaches may be caused by an HPD (primarily circumaural devices) that fits too tightly, or is in some other way uncomfortable. The HPD should be resized, refitted or another device issued.
There are no known medical or physiological reasons why HPDs should be suspected of causing any of the remaining maladies listed above. However, when an employee voices such complaints, this indicates dissatisfaction with the HPD he is wearing, a misunderstanding of the need for its use, or a real health problem that has been mistakenly attributed to the use of the HPD. The best response will be a patient and accurate assessment of the situation and determination of the actual cause of the disorder.
Question: Can I use stereo earphones for protection against noise and enjoy the music at the same time?
Response: The foam earphones offer almost no protection. Even the circumaural device provides no more than approximately 20 dB of attenuation at high frequencies, and actually significantly amplifies sounds at some frequencies. This protection is inferior to that of a well designed, properly fitted HPD. Furthermore, these devices alone can generate equivalent noise exposures up to approximately 100 dBA.
Since these devices offer so little attenuation, a greater concern is that employees might turn up the music to mask (i.e., "drown out") the factory noise. Products are available which have been specifically designed to offer adequate protection and at the same time play music or transmit voice communications. Although generally expensive, such devices are suitable for use, especially when they have built-in signal limiting circuitry so that they are not capable of presenting hazardous sounds to the ear.
Excuse: I don't need to worry about losing my hearing since I can always get a hearing aid.
Response: Although eyeglasses can in most cases correct a vision problem to a nearly normal condition, it is a misconception that hearing aids can do likewise for a noise induced hearing loss. Correctable vision problems generally result from ocular distortions and not the loss of the optic nerve cells, whereas noise damage is due to destruction of the nerve (hair) cells in the cochlea that enable us to hear. Hearing aids can restore the ability to detect and discriminate sounds to a certain extent, but when insufficient hair cells are present to receive the amplified sounds that the aid provides, the results are not fully satisfactory...and if wearing an HPD 8 hours/day is objectionable, will it be any more acceptable to wear a hearing aid (which feeds sound into the ear through an earplug like device) for all of one's waking hours?
Question: Isn't it important to wear earmuffs rather than earplugs at high sound levels? At such intensities the sound transmits directly through the bones of the skull and can bypass an earplug?
Response: Since the areas of the skull around the external ear are only a small portion of the total bone conduction mechanism, covering them with an earmuff is of small significance, perhaps 3-4 dB in the 1-2 kHz region. Thus the relative performance of plugs compared to muffs is not, in practice, determined by the bone conduction paths but by factors inherent in the design of the HPDs and their interface to the head. In fact, a well designed insert such as a foam earplug, can offer attenuation comparable to or exceeding that of earmuffs at most frequencies.
Question: Since my entire head is affected by the sound and can transmit energy to my inner ear, does a hard hat, which covers part of my skull, reduce the bone conduction?
Response: In order to block the sound and reduce the bone vibration, it would be necessary to wear a completely rigid helmet with a face plate that formed a virtual airtight enclosure about the head. A hard hat, which covers only part of the head and has many gaps through which the acoustical energy can penetrate, is of little value in reducing the ear's response to the bone conducted sound.
Question: Can I hurt my eardrum if I insert a plug too deeply or remove it too quickly?
Response: The sensitivity of the adult earcanal to pressure or pain increases significantly as the eardrum is approached. The discomfort experienced when these deeper portions of the canal are touched, will alert the user to stop pushing on the plug before the device reaches the eardrum. Furthermore, the design of most inserts will prevent inserting them the length required (about 22 mm) to touch the eardrum. A more likely problem is earwax impaction, which can result from the insertion of earplugs, particularly of the pre-molded variety. For this reason, the person fitting earplugs should visually examine the ear canal up to the depth that the plug will be inserted. Persons with chronic earwax impaction problems should consider using semi-aural or circumaural HPDs.
For plugs that create an airtight seal, such as pre-molded inserts, rapid removal can be painful and potentially damaging to the eardrum. The plugs should be removed with a slow twisting motion to gradually break the seal as they are extracted from the ear. With foam and fibrous plugs, which do not create a pneumatic seal (and hence cause less of a blocked-up feeling), there is little possibility of generating a sudden large pressure change upon rapid removal, and thus virtually no likelihood of damaging or rupturing the eardrum.
Complaint: Hearing protectors make my voice sound strange to me and make me more conscious of other body noises such as breathing and walking. They also make it difficult for me to judge how loudly to talk.
Response: This is generally true. A properly fitted hearing protection device (HPD) creates an occlusion effect which results in an increase in the ear's sensitivity to bone or tissue conducted sound. This tends to amplify internal body noises such as those generated by one's own speech and breathing. The effect is most pronounced for devices that cap the canal entrance, such as semi-aural HPDs, although it is usually noticeable for most properly fitted protectors. In fact, listening for a resonant or bassy characteristic to one's own voice while adjusting earplugs, semi-aural devices, or most earmuffs, is a useful technique to aid in attaining a good acoustic seal.
Wearing HPDs will cause most people to talk more quietly in noisy environments since the protector reduces the perceived noise level, while at the same time, due to the occlusion effect, it amplifies the apparent level of the talker's own speech. Thus, the perceived speech-to-noise ratio is distorted so that the individual believes he is speaking more loudly than actually is the case. This problem can be overcome as wearers become more experienced in the use of their HPDs and if co-workers remind them to speak up.
Question: Are all foam earplugs the same?
Response: A number of design parameters affect the performance of foam earplugs. The most important of these are the recovery characteristics of the foam and its stiffness. These properties should be optimized for best performance, and be relatively independent of humidity and temperature. If a plug expands too rapidly or is too soft it may be difficult or impossible to insert. Conversely, if it expands too slowly it may dislodge before fully seating, and if it is too stiff it will be less comfortable to wear.
A principal feature affecting the above properties is the material from which the plug is made, typically polyvinyl chloride (PVC) or polyurethane (PU). PVC is generally preferred because of stability. PU plugs tend to rapidly absorb moisture when stored in high humidity conditions or are exposed to excessive perspiration. This can dramatically speed their expansion, degrading one's ability to properly insert the plugs for optimum comfort and attenuation.
Question: Can I use noise reducing earplugs for swimming?
Response: Yes. Certain noise reducing earplugs such as those made from vinyl, closed-cell foam, silicone, and even wax-impregnated cotton can be successfully used in many cases for swimming and showering. In fact they will generally perform better than the plugs that are sold over-the-counter as "swimmer's plugs" since they fit the earcanal more comfortably and snugly. The plugs should be inserted in a dry condition, before entering the water, and the user should not submerge his head more than a few feet below the surface since this increases the likelihood of water being forced around the plug.
Question: Can I use cotton or my fingers to reduce harmful noise exposures?
Response: Occasionally one finds persons wearing nonstandard HPDs such as gum, putty, cotton, cigarette filters, empty bullet casings and other items which will not adequately seal the earcanal or simply do not possess the needed physical characteristics to effectively attenuate sound. Additionally, such devices are often uncomfortable and unhygienic. For example, ordinary dry cotton is a very poor hearing protector. Interestingly, a finger tip, although it certainly cannot be utilized for extended periods of time, does provide very good protection when forced tightly into the ear canal.
Comment: My mother always said "never put anything smaller than your elbow in your ear."
Response: This platitude is representative of the numerous preconceptions and misconceptions that many people have regarding the use of HPDs. Of course when mother delivered the above pronouncement she had in mind the pencils, pins, toothpicks, and clumsily maneuvered Q-tips® that could damage the delicate eardrum, or other miscellaneous objects that might become lodged in the ear canal. Unfortunately, she was not aware of the lasting negative mental imprint that this would create with regard to the safe and correct use of properly designed and fitted noise reducing earplugs.
References:
Berger, E.H. - The EARLog Series is available upon request from Aearo Company.
American National Standards Institute (1977). "For Rating Noise with Respect to Speech Interference," S3. 14-1977, New York, NY.
Berger, E. H. (1981). Details of Real World Hearing Protector Performance as Measured in the Laboratory. Proc. Noise-Con 81, Noise Control Foundation, Poughkeepsie, NY.
Berger, E.H. (1980). EARLog #5 - Hearing Protector Performance: How They Work- and - What Goes Wrong in the Real World, available upon request from Aearo Company.
Berger, E.H. and Kerivan, J.E. (1982). "A Rigorous Examination of the Real-Ear Attenuation at Threshold Method (125 Hz-2kHz)," J. Acoust. Soc. Am. Suppl. 1, Vol. 71, S52.
Brandell, M. E. and Seestedt, L. (1978). "Report on the Effectiveness of E-A-R® Plugs as Ear Protection in Water," Central Michigan Univ., Mt. Pleasant, MI.
Carroll, C., Crolley, N. and Holder, S. R. (1980). A Panel Discussion of Observed Problems Associated with the Wearing of Hearing Protection Devices by Employees in Industrial Environments. Proc. of a special session on the Evaluation and Utilization of Hearing Protection Devices (HPDs) in Industry, presented at the Spring 1980 meeting of the North Carolina Acoustical Society, edited by L.H. Royster. D.H. Hill Library, North Carolina State Univ., Raleigh, NC.
Caruso, V. G. and Meyerhoff, W.L. (1980). Trauma and Infections of the External Ear, in Otolaryngology, edited by M.M. Paparella and D. A. Shumrick. W. B. Saunders Co., Philadelphia, PA.
Council for Accreditation in Occupational Hearing Conservation (1978). CAOHC Manual, edited by M.H. Miller. Fischler's Printing, Cherry Hill, NJ.
E-A-RCALSM Laboratory Internal Research Notes, N2719 49.
EPA (1979). Noise Labeling Requirements for Hearing Protectors, Federal Register, Vol. 42, No. 190, 40 CFR Part 211, 56139-56147. NOTE - Regulation currently unenforced due to EPA budget and manpower reductions.
Gardner, R. Jr. (1977)."Earplugs,"U.S. Patent No. Re. 29,487. E-A-R® and brand earplugs are manufactured in conformance with this patent.
Gasaway, D.C. (1981). Personal Communication.
Gasaway, D.C. (1982). Personal communication based upon 22 years of experience supervising the USAF hearing conservation program, during which time there was not a single verifiable incident of eardrum damage due to HPD usage.
Holland, H. H., Jr. ( 1967) "Attenuation Provided by Fingers, Palms, Tragi, and V51R Ear Plugs," Letter to the Editor, J. Acoust. Soc. Am. 41(6), 1545.
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Johnson, D. W. and Maisel, R. H. (1981). "Objective Evaluation of Earplugs for the Control of Water-Borne Infection," Ann. Otolaryngol. 90, 89-93
Maas, R.B. (1972). Industrial Noise and Hearing Conservation in Handbook of Clinical Audiology, edited by J. Katz, William and Wilkins, Co., Baltimore, MD.
Ohlin, D. (1981). Personal Communication.
OSHA (1983). Occupational Noise Exposure; Hearing Conservation Amendment. Federal Register, Vol. 48, No. 46, 9738-9783.
Royster, L.H. and Royster, J.D. (1984). "Hearing Protection Utilization: Survey Results Across the USA," J. Acoust. Soc. Am. Suppl. 1, 76, S43.
Taylor, W., Pearson, J., Mair, A., and Burns, W. (1965). Study of Noise and Hearing in Jute Weaving. J. Acoust. Soc. Am., Vol. 38, 113-120.
Tobias, J. V. (1975). "Earplug Rankings Based on the Protector-Attenuation Rating (P-AR)," FAA Civil Aeromed. Inst. Report FAA-AM-75-11, Oklahoma City, OK.
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