Hearing loss is cumulative and once lost, can never be regained. The best way to protect your hearing is to create a habit of wearing comfortable hearing protection. Several types of earplugs, bands, or earmuffs are available with various levels of performance (measured as high Noise Reduction Ratings, or NRR) and most importantly, comfort for the wearer. How do we now go about protecting our hearing?

Here are some recommendations for hearing protection, whether you are a worker, safety director, purchaser, or just someone who knows it is necessary.

  1. Know your hazard. Whenever possible, measure the noise levels in your environment on a frequent basis to determine exactly what the hazards are, and have an understanding in what frequency ranges the majority of the noise occurs.
  2. Trust the annual audiogram. Rely on this information to gauge your hearing loss from year to year. Is your hearing deteriorating? Is it due to noise induced losses from the workplace, or simply the facts of aging?

  3. Select hearing protection that is right for you, that is comfortable to you, and that you will wear.
  4. Wear your hearing protection right. Each type of hearing protector is slightly different. The important thing to remember is that you need to insert earplugs correctly, or earmuffs completely over the ears. Then, you must always test the fit. To test the fit, cup your hands over your ears, then release. If you can hear a difference, you may not be wearing your hearing protector correctly. Remove, then fit again.

Following these simple guidelines can save your hearing from further hazardous exposure and potential hearing loss.

Ear Anatomy 101

In technical terms, sound is described as "vibratory energy." This energy takes the form of sound waves, which are transferred by the human ear into what we know as "hearing."

The ear has three main sections: the Outer, Middle, and Inner ear.

The Outer Ear - The outer ear directs sound waves into the ear canal, which leads to the eardrum. The eardrum then passes the waves on to the middle ear.

ear anatomy

The Middle Ear - The middle ear contains three small bones: the hammer, the anvil and the stirrup. When sound waves enter the middle ear, the pressure vibrations move the bones, creating mechanical vibrations that are passed on to the inner ear.

The Inner Ear - The inner ear contains the cochlea. The cochlea contains fluid and tiny hair cells, also known as cilia (about 35,000 in a young, healthy ear). When the mechanical vibrations enter the cochlea, the hairs respond to the vibrations in the fluid, and the hair cells pass the sensations on to the nerve fibers in the auditory nerve. From there, the nerve impulses are sent to the brain, where they are translated into what we know as hearing.

Noise Levels and Frequency

Sound can be measured scientifically in two ways. Intensity, or loudness of sound, is measured in decibels. Pitch is measured in frequency of sound vibrations per second. A low pitch such as a deep voice or a tuba makes fewer vibrations per second than a high voice or violin.

Decibels - Intensity of sound is measured in decibels (dB). The scale runs from the faintest sound the human ear can detect, which is labeled 0 dB, to over 180 dB, the noise at a rocket pad during launch. Decibels are measured logarithmically. This means that as decibel intensity increases by units of 10, each increase is 10 times the lower figure. Thus, 20 decibels is 10 times the intensity of 10 decibels, and 50 decibels is 10,000 times as intense as 10 decibels. Each increase of 5 decibels doubles the loudness in your ear. For example, being exposed to a 90 decibel noise for eight minutes is the same as being exposed to a 95 decibel noise for four minutes.

A noise level above 125 decibels can be painful. Obviously, noise at this level can cause damage to your hearing. But more importantly, noise levels between 85 and 125 decibels can cause "painless" hearing damage—damage that you may not be aware of at the time, but that can be causing permanent damage to your inner ear.

Approx. dB level Examples
0 The Quietest sound you can hear
20 Whisper, quiet library
65 Normal conversation, sewing machine, typewriter
90 Lawnmower, shop tools, truck traffic;
8 hours per day is the maximum exposure (protects 90% of people.
110 Chainsaw, pneumatic drill, snowmobile;
2 hours per day is the maximum exposure without protection.
115 Sandblasting, loud rock concert, auto horn; <
15 minutes per day is the maximum exposure without protection.
140 Gun muzzle blast, jet engine;
noise causes pain and even brief exposure injures unprotected ears.
Maximum allowed noise with hearing protector.

Frequency - Frequency is measured in cycles per second, or Hertz (Hz). The higher the pitch of the sound, the higher the frequency. Young children, who generally have the best hearing, can often distinguish sounds from about 20 Hz, such as the lowest note on a large pipe organ, to 20,000 Hz, such as the high shrill of a dog whistle that many people are unable to hear.

Human speech, which ranges from 300 to 4,000 Hz, sounds louder to most people than noises at very high or very low frequencies. When hearing impairment begins, the high frequencies are often lost first, which is why people with hearing loss often have difficulty hearing the high pitched voices of women and children.

Frequency is important because higher frequency noise can cause more damage to the hair cells in the inner ear. So, even though a high-frequency noise may only have a loudness of 85 dBA, it can cause more damage than a low-frequency noise that has a loudness of 95 dBA.

Loss of high frequency hearing also can distort sound, so that speech is difficult to understand even though it can be heard. Hearing impaired people often have difficulty detecting differences between certain words that sound alike, especially words that contain S, F, SH, CH, H, or soft C, sounds, because the sound of these consonants is in a much higher frequency range than vowels and other consonants.

How to Select Hearing Protection Devices (HPD)

Physical/Physiological Parameters to Consider:

  • Attenuation - Distinguish between:
    • Optimum Attenuation using manufacturer's reported evaluation data
    • Real-world data/expectations
    • One or both above, utilizing employee noise exposure data to compute anticipated at-the-ear levels of protected exposure
  • Comfort (short- and long-term periods of wearing)
  • Anticipated range of sizing or universal fitting capability HPDs appear to provide
  • Compatibility of HPD with user's individual anatomic/physiologic ear-head features
  • Durability and "life expectancy" (establish repair/replacement criteria)
  • Care and cleaning requirements and/or imposed hygienic restrictions
  • Portability and storage of HPD when not worn by user
  • Carrying case/container and portability (storage) between intervals of wearing or use
  • Size, weight, pressure and fitting-size adjustability factors (mechanical compliance)
  • Ease of repair, availability of replacement parts, and user's skill to accomplish or perform refurbishing tasks
  • If HPD disposable, availability of replacements, anticipated number of uses per issue, and designating strategic locations where replacements can be obtained
  • Dielectric (electrical non-conductivity) requirements/restrictions
  • Compatibility with eyewear (temple pieces)/hearing aid(s) (devices which are located in, over, or behind the external portion of each ear or surrounding head structures)
  • Cost factors ("balance" between cost and relative HPD "value" in relation to effectiveness)
  • Susceptibility to environmental contaminants or climatic extremes during storage and/or while stored or located in work areas

Ease of Use and Wearability

  • Ease and accuracy with which users can read/interpret the use, care and applications type instructions and guidance provided by the HPD manufacturer
  • Easy for user to put on, remove, and/or adjust device during wearing
  • Hygienic considerations; initial issue/use and reuse
  • Visibility: ease with which proper/improper HPD use can be identified/detected
  • Retainability within ear canal during prolonged wearing of insert plugs or ear caps
  • Retainability on/over ears/head when using muffs, ear caps, or helmet mounted devices
  • Compatibility of HPD if to be worn in confined/restricted spaces or areas
  • Climatic, meteorological, and environmental constraints and seasonal or work environment compatibility (heat, cold, moisture, etc.)
  • Compatibility with use of electroacoustic communication systems/devices

Other Considerations/Factors

  • Pre-selection trials and evaluations for judging operational end-user acceptability
  • Training, indoctrination, education and feedback among safety and health professionals, supervisors, managers, and employees regarding HPDs
  • Personal preference, aesthetic factors, color, etc. which influence acceptance or choices
  • Behavioral observations of those currently wearing HPDs (things which tend to alter or compromise the effectiveness of each type of HPD available for use)
  • On-site audits to ensure optimum HPD acceptance and performance/use
  • Dexterity of HPD users (handling and manipulating HPD and ensuring equivalency of optimum fit/wearing/insertion for both right and left ears)
  • Flammability during storage and/or after discarding (disposable devices)
  • Shelf-life during storage of new devices and/or replacement parts/units
  • Identify actions taken by some users to modify/alter HPDs original optimum condition
  • Susceptibility to abuse or intentional alteration of HPDs
  • Possibility HPDs could become foreign object(s) if dropped or purposely discarded into manufactured products; if so, select HPDs which can be electronically/mechanically detected
  • Requirement that HPD positioning in/over ears adhere to specific orientation (i.e. "top, bottom, front, back" and other orientations which may influence or confuse user placement)
  • Listening-in-noise considerations while wearing HPDs
  • Listening-in-quiet considerations while wearing HPDs
  • Defining noise exposures where use of dual protection (plugs and muffs) is required
  • Compatibility with jewelry worn on ears and/or head/face hair styles

Glossary of Terms You Should Know

"A" Weighting - Typically used in both industrial and community noise applications. "A" weighted measurements are reported in dBA. This scale corresponds to the way the human ear hears across the speech frequencies.

ANSI - American National Standards Institute

"C" Weighting - Provides a flat frequency response with slight attenuation of the very high and very low frequencies. "C" weighted measurements are reported in dBC.

CE - The CE mark is a symbol of conformity on industrial safety products that have been approved for sale in the European Union (EU). CE conformity indicates that the safety product and systems within the manufacturer’s company satisfactorily meet, or exceed, the established requirements of quality assurance, user information and on-going testing. Effective July 1, 1995, all safety products sold into the EU must be tested, approved and carry the CE mark.

Continuous Noise - The intervals of the sound waves are less than one second apart.

Decibel - A logarithmic unit of measure often used as the scale for sound pressure levels (SPL). This is perceived as "loudness or intensity."

Dielectric - Generally considered to mean a non-conductor of electricity.

Exchange Rate - The rate in which sound energy is averaged over time. Utilizing a decibel scale, every time the sound energy doubles, the measured level increases by 3 dB. This is the 3 dB exchange rate that most of the world uses. In the U.S., OSHA uses the 5 dB exchange rate.

External Ear - Consists of the Pinna or the visible portion of the ear and the external auditory canal.

Frequency - Represents the number of cycles of vibration that occur in one second. The number of cycles is designated in Hertz (Hz). This is perceived as "pitch."

Impulsive Noise - The intervals of the sound waves are greater than one second apart and are characterized by a high-amplitude, very short wave.

Inner Ear - Cochlea, semicircular canals and auditory nerve.

Linear - A sound that is a consistently flat response throughout the measured frequency range.

Mean Attenuation - The average attenuation value calculated received in each test frequency.

Middle Ear - Includes eardrum and ossicular chain (malleus, incus and stapes).

NHCA - National Hearing Conservation Association

NIHL - Noise Induced Hearing Loss due to noise exposure.

NIOSH - National Institute for Occupational Safety and Health.

NRR - NRR, or Noise Reduction Rating is a rating system set up by the Environmental Protection Agency (EPA) as a guideline that indicates the amount of potential protection a hearing protection device will give in a noisy environment. All Howard Leight hearing protection devices are tested under the Real Ear Method as directed by the American National Standard Institute (ANSI) in accordance with test procedures established by the Acoustical Society of America. All testing is performed in a controlled environment. Consequently, posted NRR ratings are a qualified example of how the individual products compare with other similar hearing protection products in an uncontrolled noise environment. Test results do not evaluate the product reusability, comfort, adaptability or quality. In the final analysis, the user must make this determination.

PHP - Personal Hearing Protection

Pinna - The visable, outer portion of the ear, which should be enclosed completely by earmuff cups.

Presbycusis - Type of sensory neural hearing loss due to aging.

PTS - Permanent Threshold Shift refers to a permanent change in hearing thresholds due to noise exposure.

Sound Level Meter - An instrument for the measurement of sound level. It consists of a microphone, a frequency selective amplifier and an indicator. It measures sound level in dB SPL.

SNR - SNR, or Single Number Rating is a rating system set up by the European Union (EU). Tests are conducted by independent testing laboratories with no direct participation by manufacturers. The independent testing laboratories meet all of the regulatory requirements as set out by the EU. The test results serve as a guideline to indicate the amount of potential protection a hearing protection device will give in a noisy environment.

TTS - Temporary Threshold Shift refers to a temporary change in hearing thresholds due to noise exposure.

TWA - Time Weighted Average. The average of the sampled sound over an eight-hour period.

Weighting - Response networks which encompass the frequency range of human hearing (10 Hz to 20K Hz). "A," "C" and Linear are the common weighting networks available.

Related Web Sites on Noise and Hearing

Acoustical Society of America (ASA)
http://asa.aip.org/
New York, NY (516)576-2360. Journal of the Acoustical Society of America (monthly)

American Industrial Hygiene Association (AIHA)
http://www.aiha.org/
Fairfax, VA (703)849-8888. American Industrial Hygiene Association Journal (monthly)

American Speech-Language-Hearing Association (ASHA)
http://www.asha.org/
Rockville, MD (301)897-0135. ASHA (quarterly)

Council for Accreditation in Occupational Hearing Conservation (CAOHC)
http://www.caohc.org/
Milwaukee, WI (414)276-5338. CAOHC Update (3x / year)

Institute of Noise Control Engineering
http://www.inceusa.org/
Poughkeepsie, NY (914)462-4006. Noise Control Engineering Journal (bimonthly), Noise/News International (quarterly)

National Hearing Conservation Association (NHCA)
http://www.hearingconservation.org/
Milwaukee, WI (414)276-6045. Spectrum (quarterly)

Noise Pollution Clearinghouse
http://www.nonoise.org/
Montpelier, VT (888)200-8332

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