Some common sense advice 
on hearing protection

Use this article to form the basis of an in-house training class

Noise-induced hearing loss is a disabling injury. Imagine going through the rest of your life without the ability to communicate with others, enjoy your favorite music, or simply appreciate the subtle sounds of nature. OSHA estimates that as many as 15 million Americans have a measurable hearing loss and that 30 million workers are exposed to potentially hazardous noise levels on the job. Proper selection and use of personal hearing protection devices significantly reduces the potential for noise-induced hearing damage.

OSHA regulations are designed to protect workers from noise exposure hazards. The original OSHA regulation has been in effect since 1971 and amended in 1981 to include additional requirements, including the establishment of an effective hearing conservation program. This amended regulation, 29 CFR 1910.95, has been in effect since 1983.

To better understand how hearing can be damaged, we need to first understand sound and noise. Sounds are variations in air pressure detected by the human auditory system. Noise is simply unwanted sound. High levels of noise damage hearing and impair the ability to hear sounds such as warning alarms and verbal communications from coworkers. Wear hearing protectors in these noisy environments to reduce the noise at the ear to an acceptable level without needlessly impairing communication.

Two distinct characteristics describe sound or noise--amplitude and frequency. Amplitude is the technical term for the volume of the sound, that is, louder sounds have greater amplitude. Obviously, louder sounds have greater potential for inducing hearing loss than quieter sounds. The amplitude of a noise source is measured on a logarithmic scale with units of decibels (dB) and is usually referred to as sound pressure level. This scale is used because the human ear is responsive to such a wide range of sound pressures that other units of measure are cumbersome and awkward to use. The decibel scale, on the other hand, reduces this wide range to an integer that ranges from about 0 to 140.

The A-weighted decibel scale, or dBA, is often used in industrial noise applications because it more accurately reflects the damaging potential of the noise. The dBA scale de-emphasizes lower frequency sounds since they are less damaging than higher frequency sounds of thesame amplitude.

TWA refers to the Time Weighted Average over an eight hour workday. OSHA considers time weighted average exposures of 90 dBA and over to be hazardous (see Figure 1). Most experts agree that noise exposures should be limited to 85 dBA whenever possible. Even brief exposure to extremely loud impulsive noise such as gunfire can cause permanent noise-induced hearing loss. A person's susceptibility to noise-induced hearing loss varies. In other words, two people working in the same noise exposure for the same length of time may experience quite different degrees of hearing loss.

Hearing protectors are only effective if they are worn for the entire duration of the noise exposure.

Sounds are comprised of many separate components, each of which may have a primary frequency. That is, most sounds are the combination of many high, low, and middle frequency sounds. These frequency components are measured in cycles-per-second, or Hertz (Hz). On a piano, the primary frequency of the A note above middle C is 440 cycles per second, or 440 Hz. Cycles per second correspond to variations of air pressure caused by the sound source. Industrial noise sources typically range from about 60 to about 10,000 Hz.

The human auditory system is capable of hearing sounds from about 20 to about 16,000 Hz. It should be noted that most of the useful information occurs below about 10,000 Hz. For example, speech information is in the range of about 125 to 6,000 Hz. When noise-induced hearing loss occurs, the loss usually becomes evident in the higher frequencies first, typically around 4,000 Hz. From there, the loss spreads upward and downward in frequency. Along with the reduced ability to hear sounds, there are other problems associated with noise-induced hearing loss. To the hearing impaired, audible information often sounds garbled or confusing. Ringing in the ears--tinnitus--may accompany high-level noise exposure. Chronic tinnitus is particularly debilitating for some people.

Hearing loss occurs when the eardrum and the small bones of the middle ear relay high levels of sound energy to the inner ear. The primary structure in the inner ear is the cochlea. This structure has thousands of tiny hair cells that respond to vibrations in the inner ear fluids. The cochlea is spiral shaped and the hair cells extend from the base (bottom) to the apex (top) of the spiral. The hair cells respond to different frequencies depending on their location. Hair cells at the base of the cochlea respond to high frequency sounds and hair cells at the apex of the cochlea respond to lower frequency sounds. The hair cells may be damaged by excessive noise exposure. Long-term exposure to high levels of noise eventually kills some of these hair cells, resulting in hearing loss in the corresponding frequency regions. Other maladies associated with high level noise exposure include increased levels of stress and anxiety, elevated blood pressure, increased susceptibility to illness, sleep problems, headaches, and tinnitus.

While OSHA tries to protect workers by establishing a time weighted action level of 85 dBA and a time weighted permissible exposure limit of 90 dBA, there are no such regulations that govern noise exposure during time away from work. Noise exposure during leisure activities increases the hazardous effect of ones workday exposures. Activities with power tools, chain saws, or guns obviously have the potential to damage hearing. Other potentially hazardous activities include auto racing and loud music. During loud activities, it is easy and inexpensive to protect hearing with personal hearing protection.

Hearing protector ratings
Proper selection of hearing protection is important. The device must be comfortable, fit correctly, and provide adequate protection from the wearer's noise exposure. The EPA mandates that hearing protectors be labeled with a Noise Reduction Rating. While this number is a general indicator of the effectiveness of a protector, do not base your selection solely upon the Noise Reduction Rating of the device.

The Noise Reduction Rating of a hearing protector is derived from testing procedures outlined in the American National Standards Institute standard S3.19 - 1974. These tests require a controlled laboratory setting and the noise reduction measurements may be quite different than the actual noise reduction provided in work environments. Many factors account for this difference, including poor training and motivation of the hearing protection device wearers, improper fitting, and physical characteristics of the hearing protection device user that prevent a good fit. Hearing protectors are only effective if they are worn for the entire duration of the noise exposure. If the protector is removed for even brief periods during the noise exposure, the effective protection drops dramatically, resulting in a potentially hazardous noise exposure. For these reasons, selecting a comfortable and properly fitted hearing protector is critical.

The right protector
Choosing the correct hearing protector can be confusing considering the vast array of types, styles and sizes. Select hearing protectors that provide sufficient protection while not unnecessarily degrading the ability to communicate. The safety products supplier or hearing protection manufacturer is a valuable asset during the selection process.

Most manufacturers have a well-trained, experienced technical service department to assist you in the hearing protection device selection process. These experts will base recommendations on your specific noise exposure and other requirements. There are other sources of information available to you as well, including your local OSHA Consultation Office, regional OSHA office, National Institute for Occupational Safety and Health, National Hearing Conservation Association, and the American Industrial Hygiene Association.

Begin by choosing the type of protection suitable for your application. This selection will be limited to an earmuff, a semi-aural protector, or an insert-type device--an earplug. Hearing protection devices range in price from just a few cents for disposable foam earplugs to several hundred dollars for electronic earmuffs. Obviously, these products provide widely ranging levels of function, comfort, ease of use, durability and protection.

Muff-type protectors
Earmuffs can be either active or passive devices. Active protectors incorporate either electronic or mechanical components to limit or cancel noise. Passive earmuffs simply attenuate or block out sound by acting as a barrier. Muffs are considered by some to be the most comfortable selection for general long-term application, although their use in hot or confined areas should be avoided.

Muffs require periodic maintenance to perform properly. This maintenance includes inspection and possibly replacement of ear cushions, cup insert materials, and the batteries in electronic muffs. Monitor the strength of the headband. Stretching the headband beyond normal limits on some models compromises the overall effectiveness of the muff.

Communication capabilities are currently available in muff-type devices, including compatibility with pagers and two-way radios. Some models include microphones and built-in amplifiers that allow communication during periods of relative quiet while reducing high noise levels, including hazardous impulse noises such as stamping machines or gunfire.

Muffs with frequency-specific attenuation block out certain frequencies while allowing transmission of others. These devices may be more suitable in specific noise environments than traditional muffs and they may also allow superior speech communication under some noise conditions. Advances in earmuff technology include linear attenuation devices and active noise cancellation products. Noise Reduction Ratings for muff-type devices range from about 16 to 30 dB, and prices can run from less than $10 for economy, general purpose muffs, to around $40 for frequency-specific passive muffs, to as much as $400 or more for active noise cancellation devices (1998 prices).

Most models of muff-type protectors are available in both standard headband configuration and as attachments to safety caps. In standard headband form, some models may be worn with the headband in three positions, over-the-head, under-the-chin and behind-the-head. When worn in the under-the-chin or behind-the-head positions, it may be useful to use a crown strap to stabilize the device. This strap connects to both cups and is worn over the top of the head.

Stretching the headband beyond normal limits on some models compromises the overall effectiveness of the muff.

Semi-aural hearing protectors are available in several styles, each of which incorporates a headband that holds the protectors in place. The protectors may be conventional earplugs, modified versions of conventional plugs, or devices that block out noise by sealing off the entrance to the ear canal. Because this protector usually is not inserted deep into the ear canal, it reduces the discomfort created by the outward pressure of an expanding plug. Semi-aurals are often preferred by individuals that need intermittent protection, as the devices can be easily removed and re-fit. When not in use, they are often worn around the neck. Another advantage of this type of protector is that it is possible for individuals in dirty environments to remove and re-fit the protector without touching the plugs themselves. This reduces the possibility of introducing dirt into the ear canal. Noise Reduction Ratings for semi-aurals range from about 16 to 26 with prices between $3 and $10.

Earplugs
Earplugs are available in many sizes, shapes, colors, and materials. Reusable earplugs are usually made of silicone or polyvinylchloride materials for durability. Disposable plugs are usually constructed of a polyvinylchloride or urethane foam material. Multiple-sized plugs may be preferable for optimal fit, comfort, and protection. It is more likely that a large population of individuals will be properly fitted with a multiple-sized plug than with a single-size device.

Most earplugs are available with or without cords. These cords are worn around the neck, with the intention of preventing the wearer from accidentally dropping or losing the plugs. Select metal-detectable plugs if the wearer is involved in a sensitive process such as food processing or pulp manufacturing. The best choice in this situation is a protector that is completely detectable. Should the protector be cut or chopped into smaller pieces, all the pieces remain detectable by metal scanners. Prices for detectable plugs range from $1 to $3 per pair with Noise Reduction Ratings from 15 to 33.

Disposable earplugs constitute the bulk of the hearing protectors in use today, in part due to the low price (about 10 to 20 cents per pair). When the total cost of using one or more pairs of disposable earplugs per day is considered, disposable plugs may be more expensive than reusables. Disposable earplugs usually are not considered to be the most comfortable hearing protector, especially foam-type plugs that require rolling and deep insertion for maximum protection. The expansion of the foam produces outward pressure in the canal, leading to discomfort for some wearers. The transfer of dirt from the users' fingers to the earplug during rolling and subsequent insertion into the ear canal also leads to the possibility of irritation or infection. Non-foam earplugs exert less outward pressure on the canal and are less likely to carry dirt into the canal during fitting.

Disposable earplugs are typically labeled with very high Noise Reduction Ratings. While this rating may appear desirable, using hearing protection devices with ultra-high noise reduction is not required in most job settings. Using high NRR products in environments where they are not required may result in overprotection that unnecessarily reduces the ability to hear warning signals or verbal communications.

Muffs with frequency-specific attenuation block out certain frequencies while allowing transmission of others.

Remember that these calculations are only valid when the protector is used properly and in accordance with the manufacturers instructions. In addition, the hearing protection device must be worn during the entire duration of the noise exposure. If the wearer removes the protector during the noise exposure, the effective level of protection is reduced drastically. For instance, if a protector with a Noise Reduction Rating of 30 is removed for a total of just 30 minutes during an eight-hour workday, the effective protection is reduced to less than 50 percent of the Noise Reduction Rating (see Figure 3).

Multiple-sized plugs may be preferable for optimal fit, comfort, and protection.

In summary, effective hearing protector use requires the proper training and selection of comfortable devices that allow 100 percent wearing time. In other words, The best hearing protector is the one that gets worn.