Hearing protection

AN EARFUL OF SOUND ADVICE

By Hayley Chandler

What’s the best hearing protection you can buy? With all the types and styles available, the answer may still surprise you.

Hearing protection is near the top of the list when it comes to safety purchasing in many workplaces. The basic purpose of all hearing protection, of course, is to reduce the amount of damaging noise that makes it through to workers’ ears. But there’s a lot more than just noise reduction to consider when deciding what type of hearing protection to provide for workers. "All of the protectors have lots of attenuation so let’s set that consideration aside. Look at how people use them and what’s suitable in the work environment," says Christine Harrison an occupational audiologist with the Workers’ Compensation Board of British Columbia.

Factors to consider include the following:

* The worker’s average daily exposure to noise, not the noise level generated by a certain piece of equipment or in a particular area

* The worker’s hearing ability. A hearing-impaired worker may require a special protector or one with lower attenuation.

* The communication demands on the worker, such as the need to hear speech or warning signals.

* Compatibility with other PPE.

* Temperature and humidity levels. Earplugs are more comfortable than muffs in hot environments.

* Any constraints due to the worker’s physical features or activities.

As well, the personal preferences of the people who have to use hearing protection are an important factor -- the important factor, in some cases. Issues of comfort and convenience have a direct bearing on compliance -- making sure that hearing protection gets used. Fortunately, there is a wide variety of equipment available. "The best hearing protection is what the individuals will wear," says Nancy Comber, product manager, hearing and communication systems for Arkon Safety Equipment Inc. in Mississauga, Ontario.

Hearing protection devices can be divided into three categories: earplugs, which are placed in the ear canal, semiaural devices (commonly known as semi-inserts, canal caps or hearing bands), which are held against the entrance to the ear canal with a head band; and earmuffs, which fit over the ears.

As well as coming in a wide variety of styles, hearing protectors offer varying levels of protection. Hearing protectors are rated according to Canadian Standards Association Standard Z94.2 Hearing Protectors. The standard assigns protectors to one of three classes of protection -- A, B or C -- based solely on attenuation values. (Attenuation is the amount by which a hearing protector reduces the sound level at the ears of a person wearing the protector.) Class A protectors provide the greatest attenuation. Class C protectors offer the least.

The noise reduction rating, or "NRR", system is used in the United States. Hearing protectors bear an NRR number. The higher the NRR, the higher the attenuation of the protector. "Officially [the NRR system] doesn’t have a place in Canada," says Christine Harrison. "But it’s usually on products, particularly if they’re packaged in the U.S., so [Canadians] see the number," she says. Alberto Behar, a Scarborough, Ontario based consultant specializing in noise control and hearing conservation observes, "Many of them don’t care about the ABC ratings; they care about NRR."

The NRR system assigns a simple rating number to each type of hearing protector. A package of earplugs, for example, might bear the notation "NRR 26". (The usual range for most protectors is about 20 to 33.) This suggests that the noise level reaching the ear is reduced by 26 decibels. However, hearing protectors respond differently to different frequencies of sound; the attenuation at lower frequencies is typically lower than for higher frequency sounds. The Canadian "ABC" rating system attempts to take this into account by establishing a range of attenuation for different frequencies.

Both systems seem simple and straightforward, so choosing the right level of protection should be easy. Unfortunately, neither rating systems is all that accurate. "The NRR is derived under laboratory conditions -- meaning ideal," explains Harrison. "The people who are used to determine the attenuation values are seated and the hearing protectors are placed on them by other people," she says. In this way, the tester ensures the hearing protectors are worn and working properly. "It doesn’t approximate real life in many ways. The ABC system is based on those same measurements but there’s a little more range," she adds.

"We are dealing with lab data that is far away from what you get in real life," says Behar. "We are playing with numbers that are meaningless." To allow for a safety margin, some organizations use 50 per cent of the NRR as the expected noise reduction factor under workplace conditions. The issue was recently addressed by the American National Standards Institute (ANSI). It published a new standard in 1997 (ANSI S12.6-1997 Methods for Measuring the Real-Ear Attenuation of Hearing Protectors) that uses a testing method that provides results much closer to what you find in the real world. Test subjects who are not used to wearing hearing protectors are asked to put the protectors on themselves with only the manufacturer’s instructions for guidance. "In that respect, I think the American standard is a breakthrough. It will give us numbers that are much more realistic," says Behar. The CSA standard is scheduled for review next year and the validity of the ABC system will likely be reviewed at that time.

Common mistake

A second problem concerning selection has to do with human nature rather than statistics. Many purchasers believe that workers are best protected by the device with the highest possible attenuation. This is not true. When it comes to choosing hearing protection, less is more. "You don’t buy A-level [protectors] unless you need them," says Behar. "Usually people put a Class A on and it blocks out so much sound, it’s almost scary," says Harrison. They remove the overly powerful protectors because there are sounds they want to hear, exposing themselves to risk. "When the equivalent noise in a work area is less than 89 to 95 dBA, it may be appropriate to select Class C or Class B protectors respectively (rather than Class A), since their reduced attenuation may provide for improved warning-signal detection and speech discrimination, especially for people with hearing handicaps," says the CSA. In other words, workers are more apt to continuously use hearing protection that has lower overall attenuation.

"Very few workers have exposure levels above 95dBA," observes Harrison. In B.C., we estimate five per cent of workers (including those in jobs such as mining, construction and forestry) have exposure levels over 95dBA, she says. "Meaning 95 per cent of the work force could go into the purchasing procedure looking for Class B first."

Unfortunately, the convenient and very popular foam earplug is only available as Class A protection. "What I’d like to see is a Class B foam earplug," says Harrison. "That’s my challenge to the earplug manufacturers," she says. "Make a foam earplug that has less attenuation."

Earplugs are made in a variety of shapes and materials. They can be reusable or disposable. Mass-produced styles may be moldable (these are rolled between the fingers and compressed before insertion into the ear, where they expand to make a good seal) or premolded (already formed to fit the ear). Earplugs that are custom molded to fit each worker’s ear canal are another option, especially useful for workers who are hard to fit off the shelf.

Moldable earplugs are made from a variety of materials. "The most popular type of plug available is a foam ear plug," says Elliott Berger, senior scientist, auditory research for E-A-R Hearing Protection Products in Indianapolis, Indiana. "Foam plugs tend to be among the most protective and the most comfortable," he explains. "There are vinyl foam earplugs and urethane foam earplugs." Of the two, Berger feels vinyl "offers a better balance" in that it is "sufficiently stiff that you can roll it down and get it in your ear properly and yet soft enough to be very comfortable." Urethane plugs tend to feel a little softer in the hand but they’re a denser material so they are no more comfortable in the ear, he says. Urethane earplugs are molded so they can be made in attractive shapes (vinyl ones are punched out of sheet material). While that doesn’t contribute to the performance, it makes the earplugs look nice. "Sometimes that’s an important feature to motivate someone to purchase or use a product," Berger says.

Premolded plugs are made from flexible materials in shapes engineered to fit the ear. They do not have to be compressed or shaped prior to insertion. These plugs are available in different sizes and some workers may even require a different size for each ear. Many models are designed with flanges, which give the plug a more adaptable fit. Generally the more flanges a plug has the fewer sizes are required to fit the worker population. Most premolded plugs are available with attached cords, which allows workers to hang them around their necks and helps to prevent loss. "The protection is generally a little bit less and the comfort is generally not quite as good as with a foam ear plug," says Berger.

Custom-molded earplugs are specially made for each worker, which should result in comfort and ease of insertion. "It’s pretty hard to put them in wrong," says Nancy Comber, of Arkon. They are also the most durable earplugs available. However, they cost more than mass-produced plugs and can’t be made without worker involvement. "With a custom-molded plug there’s no noise reduction rating available for companies to use as a baseline for what protection they’re offering to their employees," says Comber. There’s also a potential problem concerning fit. "If a person has a cold or a sinus infection or they lose weight, it can affect how that custom-molded piece fits in their ears," Comber states.

Semiaural devices

Semiaural devices consist of flexible tips attached to a lightweight headband. They are often identified as "canal caps" or "semi-inserts" because the cap or tip partially enters the ear canal to provide a seal. Unlike earmuffs, which are much bulkier, they can be worn in close quarters, and safety glasses or hard hats do not compromise their fit. However they may lose their seal if the band is bumped or moved. They offer less protection than either plugs or muffs and the force of caps pressing against the canal entrance can make them uncomfortable for continuous, long-term wear. Because of the way they cap the ear canal, they tend to distort worker’s perception of their own speech more than other types of hearing protection devices.

Earmuffs

Earmuffs consist of a pair of hard outer cups, lined with sound-attenuating material, that are held together by a headband. Cushions seal the cups around the ear. Earmuffs vary with respect to the material and depth of the dome, the material filling the cushion, and the force and versatility of the headband.

"In a laboratory scenario, you get more low frequency attenuation with bigger cups, but in practice it’s not usually of that much benefit, and the extra cost, the size, the weight, and the decreased comfort in general would argue against the larger cups except for very high noise levels," says Berger.

Some headbands may be used in only one position. Other styles will function over the head, behind the head or under the chin. "You want to select a muff that easily adjusts so that you can adapt it to fit well on your head and provide equal pressure in front, behind, above and below the ear so that it seals properly," says Berger. Earmuff performance will be reduced by anything that interferes with the seal around the ear, such as hair, eyewear, masks and hard hats.

Blocking noise not sound

"Conventional hearing protectors block out all sound and that may be good or that may be problematic," says Christine Harrison. The problem is that workers often need to hear sounds while being protected from noise. They may need to communicate with co-workers or hear warning signals. To address this problem there are several types of special hearing protectors that offer both acceptable attenuation and improved communication and signal reception.

These amplitude-sensitive protectors fall into two broad categories: active and passive. Active protectors incorporate electronic components. The types of active protectors that use electronic amplification are known as variable attenuation, nonlinear or level-dependent protectors. While they block out hazardous noise, a microphone picks up quieter sound outside the earmuff and transmits it to a small speaker inside which amplifies the low noises so workers can hear sounds such as conversation and signals. In some models, amplification is maintained at a predetermined level, in others it can be adjusted by the wearer. When the sound level gets dangerously high, the electronics start to act as a limiting device and don’t permit further amplification. This type of device is available with one (monaural) or two (stereo) external microphones. Workers who need to locate the source of sounds should use the stereo version.

Passive protectors -- either plugs or muffs -- have specially designed air valves to generate turbulence when large sound waves pass through them. As a result, the noise level of the waves decreases. The reduction in noise is proportional to the sound level of the wave. There is little attenuation at levels below 90 decibels. Because passive protectors have no electronic components and do not require batteries, they are less expensive, more durable and require less maintenance than active protectors.

Another variation of this type is the flat attenuation or "musician protector" -- yes, some members of symphony orchestras wear hearing protection. "The flat attenuation protectors block out everything equally. They have the effect of just turning the volume down," says Harrison. Flat attenuation protectors are available as plugs and muffs. Presently, there are no standards to quantify the performance of amplitude sensitive hearing protectors. However, "the ISO is working on such documents," reports Berger.

Whatever the noise, an orchestra or a jackhammer, the choice of hearing protection depends on many variables -- not least of which is the user’s preference.

Hayley Chandler is associate editor of safety purchasing for OHS CANADA.

box

BUYING TIPS

* It is often most effective to provide a whole range of options to workers. Sample packs of various kinds of earplugs are available from your safety equipment distributor. These will allow workers to choose the type, style and even colour with which they are most comfortable. (Allowing a little individual expression, and possibly better fitting, in choice of plugs will go a long way in overcoming workers’ reluctance to comply with a blanket policy.)

* Ear bands, which can be worn around the neck when not in use, are the ideal choice for people who spend short periods of time in the noise area, or who merely walk through it once or twice a day. While they might not require hearing protection from a daily exposure point of view, the issue of visible compliance is an important one. In other words, even visitors should be seen to be wearing hearing protection if it is a blanket policy for the noise area. Hearing bands can be put on and taken off quickly, with a minimum of fuss.

* Workers who will ordinarily wear protective gloves against chemical exposure, or who usually have dirty hands should not use earplugs. The risk of transferring a contaminant to the plug -- and thus to the skin of the ear canal -- suggests that earmuffs are a more appropriate choice.

* Workers exposed to "impact noise", or very loud, intermittent bursts of sound similar to gunshots, can use plugs or muffs specially designed to reduce the effects. Rather than deadening all sound (impact noises are often at 140 dBA or more), these hearing protectors filter out only the very loud noise and allow for nearly normal hearing the rest of the time.

* Detectable plugs are a good option for those in the food processing industry who want to protect against contaminating the product with dropped earplugs. These plugs are generally available in a "non-food" colour -- often bright blue. They also have a piece of metal imbedded or attached to them so that they can be located by metal detectors during quality screening.

* Workers who routinely wear head protection should consider ear muffs that clip into the slots on a standard hard hat. This makes it fast and easy to wear both. However, attachment arms are not as adjustable as headbands and they cannot fit as wide a range of workers.

* Disregard small differences in noise reduction ratings (NRRs). Differences in the NRR of less than three dBA have no practical importance. Even four and five dBA differences are of questionable significance.

* Generally, foam earplugs, ear muffs, or a combination of the two are the types of devices that offer the most protection at high noise levels.

* Before purchasing a particular style of earmuffs, ensure that other personal protective equipment such as eyewear, hard hats or respirators, does not interfere with the seal.

* If you are concerned about monitoring compliance, consider that earmuffs are much easier to see than earplugs.

* The CSA advises that in general, reusable earplugs should be replaced at least every six months, and earmuff cushions should be replaced at least every year.

Top

Back to contents