Over the past several decades there have been major advances in the regulations governing hearing protection for industrial workers, in the products designed to provide that protection, and in the educational programs to ensure compliance and to inform workers of the importance of protection. Despite these efforts, the incidence of noise-induced hearing loss in the workplace continues to rise. A recent National Health Interview Survey showed that from 1971 through 1990, hearing problems among individuals ages 45-64 increased 26%.1 Other studies estimate that 10 million US workers have already lost part of their hearing and that as many as 30 million more may be at risk.2

The Four C’s of Hearing Protection
One reason for this is that too little attention has been paid to the human dimension of industrial hearing safety. Hearing health is a quality-of-life concern on and off the job.3 Our research has identified four factors that govern worker acceptance and use of hearing protection on the job. We call these factors “the Four C’s” of hearing protection: Caring, Comfort, Convenience, and Communication.

Caring. A better understanding of how workers view noise, and how they actually use hearing protection devices on the job can help improve the track record for hearing conservation programs. While the “Caring” aspect may remain the challenge of education programs, advising patients on several new material technologies that are being incorporated into the design of hearing protection devices can also definitely facilitate the other three C’s.

Comfort and Evolving Materials Technology. The best hearing protection device in the world will do little good if it is not worn properly or at all, and Comfort—or the lack of it—is the reason workers most often cite for not wearing hearing protectors. This is especially true with earplugs, which are rather invasive and provide a more intimate usage experience than other hearing protection products. Earplugs require proper insertion to be effective, often requiring workers to roll them down prior to insertion, then wait for them to expand before they enter hazardous noise areas. No two workers are alike, either anatomically or in their preferences, and an earplug that provides all-day comfort for one, may cause unendurable aggravation for another.

 Figure 1. New no-roll TPE disposable foam earplug models, like Matrix® (above), are molded with a soft outer skin and a firm inner core to facilitate insertion. They require no waiting and are effective immediately, reducing the temptation not to use hearing protection for short-term exposure.

This problem has provided an interesting challenge to manufacturers who have sought to meet it with an increasing array of styles, sizes, and designs. New materials are also influencing increased comfort levels. Disposable polyurethane earplugs (Figure 1) have largely replaced many of the old PVC barrel types, due to the increased softness and comfort they provide. Contoured designs also fit more comfortably than cylinder-shaped earplugs, and new, low-pressure foam earplugs with smaller diameters work well for those who have smaller ear canals like female workers.

 Figure 2. Reusable earplugs featuring new materials like thermoplastic elastomers (TPEs), improve both comfort and function. For example, Howard Leight SmartFit™ earplug has optimized the materials blend so that the earplug conforms precisely to the shape of the user’s ear canal, providing greater comfort for longer periods of time.

In reusable earplugs, new materials like thermoplastic elastomers (TPEs) are providing even greater benefits in both comfort and function (Figure 2). TPEs were first introduced in the early 1980s as a rubber-like material that could be processed using mass production methods such as injection molding and extrusion. They contain varying degrees of rubber compounds dispersed in a polymer matrix. The combination of the soft rubber compounds and the rigid polymer matrix yields a material that optimizes the fit characteristics and performance of a reusable earplug. These TPE materials have the soft flexible component that assists the fit characteristics of a reusable earplug to the unique ear canal of every user. The rigid component primarily provides for maximum attenuation properties. TPE materials are designed to combine the sound dampening qualities of rubber with the economy and manufacturability of plastic.

The material can be formulated to produce a very soft, comfortable earplug, and one design has optimized the blend so that the plug actually softens and changes shape as it reaches body temperature. This allows the earplug to conform precisely to the shape of the user’s ear canal, providing much greater comfort for longer periods of time. Users report they frequently forget the plugs are in their ears, and often express surprise the first time they remove them to discover their left ear canal has a different shape than their right.

Convenience. Convenience is another factor in hearing protection usage. Because we live in an age of instant gratification, and because many workers tend to consider noise hazards less seriously than other workplace hazards, any inconvenience in obtaining or using hearing protection devices can lead to a breakdown in safe work procedures. Convenience depends on two factors: availability and ease of use.

Availability is a question of supply, but ease of use is another area where new design and materials technology can help increase worker compliance. Many workers consider the act of rolling an earplug down, inserting it and then waiting for it to expand to be a bothersome procedure. If they are in a hurry, or only plan to be in a noise hazard area for a brief time, there is a strong temptation not to bother or insert them too quickly. Improper fit reduces the optimum attenuation an earplug can provide, thus allowing harmful noise to leak into the ear canal. Since repeated short-term exposure or a reduction in optimum attenuation can often be as damaging as steady exposure, ease of use plays a critical role in the effectiveness of any hearing protection product.

The new no-roll TPE disposable foam earplugs offer an excellent solution in this type of situation. Molded with a soft outer skin and a firm inner core to facilitate insertion, they require no waiting and are effective immediately. New corded models offer the added convenience of allowing the earplugs to hang around the neck when not in use, as do a number of banded and corded reusable earplugs.

Communication. The last of the four C’s—Communication—ranks right next to comfort as a key factor in hearing protection usage. Humans are social animals who want and need to communicate on the job. A common concern is that workers can’t hear anything when they are wearing hearing protection. There is admittedly a certain irony in this, but there is also a growing body of evidence that suggests a link between the inability to hear while wearing hearing protection and the incidence of industrial accidents.

Certainly it requires no great leap to accept the idea that a worker who cannot hear the warning sounds of equipment backing up or the shouts of his fellow workers is at greater risk than one who can hear these sounds. Not only is this a worker safety risk, it is also a risk for companies in terms of liability and worker’s compensation. But even in situations of less immediate risk, workers will frequently remove an earplug or pull an earmuff aside to hear instructions or simply have a conversation with a fellow worker. This, of course, exposes them to hazards from intermittent noise. Workers who wear earplugs made of advanced TPE foam experience a noticeable difference in their ability to talk and listen to each other on the job. New TPE materials used in no-roll disposable earplugs allow more speech frequencies to pass through while still blocking out high decibel noise.

 Figure 3. Earmuff designs that generate a uniform attenuation profile, like Bilsom’s Clarity™, rely on both material usage and a patented cushion and back plate design that controls the way air—and hence sound—travels through the earmuff and enters the user’s ear. This allows users to hear the speech frequencies more naturally, and makes workers feel less isolated on the job.

Electronic earmuffs have been available for some time, and provide excellent communication capabilities for workers, albeit at a relatively high cost. But new material technology and device design are now providing similar solutions more economically. Of growing promise are earmuff designs that generate a “uniform attenuation profile.” Standard earmuffs tend to block high frequencies more readily than low. Since a large percentage of hazardous noise is of low frequency, these uniform attenuation earmuffs have the net effect of blocking more harmful sounds while allowing easier passage for higher frequency sounds, such as human speech (Figure 3).

 Figure 4. One new technology resulting from advanced materials research is called “uniform attenuation.” This enables hearing protection devices to filter harmful noise while allowing other sounds, like human voices and alarms, to pass through more easily.

The effect is achieved through both material usage and a patented cushion and back plate design that controls the way air—and hence sound—travels through the earmuff and enters the user’s ear. This is designed to provide a resonance shift that results in an attenuation profile which allows users to hear the speech frequencies more naturally. This makes workers feel less isolated on the job, improves productivity, and provides them with better hearing protection (Figure 4).

Another way in which advanced materials foster better protected communication is through targeted attenuation. For many years manufacturers raced to see who could provide the highest attenuating product. Now, by taking more human factors into the equation, it’s clear that bigger isn’t always better. By varying the formulations of these newer products, we can produce both earplugs and earmuffs in a variety of noise reduction ratings (NRR). This allows employers to provide a level of protection appropriate to their environment without the problems associated with overprotection.

These are only a few of the initiatives underway in the hearing protection industry. It’s possible to do more than just block sound; there are many more exciting developments waiting to be uncovered in the field of occupational hearing conservation.

This article was submitted to HR by Edwin Woo, vice president of global research and development at Howard Leight Industries (A Bacou-Dalloz Company). Correspondence can be addressed to Edwin Woo, 7828 Waterville Rd, San Diego, CA 92154; email: [email protected].

1. Summary Health Statistics for US Adults: National Health Interview Survey, 2002. Vital and Health Statistics, Series 10, Number 222, Washington: US Dept of Health and Human Services; Hyattsville, MD: National Center for Health Statistics; July 2004, DHHS Publication (PHS) 2004-1550.
2. Franks J, Stephenson M.R., Merry C.J. eds. Preventing Occupational Hearing Loss—A Practical Guide. Washington: US Dept of Health and Human Services; June 1996.
3. Kochkin S, Roger C. Quantifying the obvious: The impact of hearing instruments on quality of life. Hearing Review. 2000;7(1):6-34.