Bad Assumptions about Hearing Protection Can Be Hazardous, Injurious

Feb. 1, 2010
News from the International Safety Equipment Association

In the world of personal protective equipment (PPE), bad assumptions are hazardous and often injurious. Unfortunately, despite 25 years of solid regulation, some persistent bad assumptions are very widespread in hearing conservation programs (HCPs). Here are six of the most common bad assumptions about hearing protection for noise-exposed workers. Perpetuated unchecked, these assumptions torpedo an otherwise healthy HCP and leave the door open for hearing loss among workers exposed to hazardous noise.

Assumption 1: Hearing protection is self-explanatory.

Assuming that proper use of hearing protection is fairly intuitive (“just put it in your ear…”), many safety managers provide little or no training in how to use protection properly.

Repeated studies show that the most effective use of hearing protection comes after one-on-one training. Large group training in hearing protection seems to have little effect in proper usage; only individual training can be linked to high attenuation results.

For proper fit of earplugs, the fitting steps are not complicated. A simple three-step process conveys the essence of a proper fit for foam earplugs: Roll, Pull, Hold. Roll down a foam earplug into a small crease-free cylinder, pull the outer ear up and back to open the ear canal, insert the earplug and hold in place while it expands.

For proper fit of earmuffs, move aside any thick hair, and seat the earmuff so that it encloses the entire ear. Avoid safety glasses with thick temple bars at the frames. For safety eyewear or prescription glasses with a thin frame (a width of two millimeters or less at the temples where the earmuff cushion meets the frame), eyewear causes no significant decline in attenuation. But safety eyewear with wider frames causes noticeable gaps in the cushion seal, resulting in a loss of attenuation of 5-10 decibels (dBs) in some cases. (For additional information, see Earmuffs & Safety Eyewear, a technical bulletin posted on the Howard Leight website).1

Assumption 2: Any earplug in the ear is blocking some noise.

It simply isn't true. An earplug just sitting in the bowl of the outer ear, without sealing the ear canal, is nice ear decor — but it is offering little protection from noise. In fact, attenuation measurements show that a poorly fit earplug often creates a resonance cavity in the ear canal, actually increasing the noise level by a few decibels (similar to cupping your hand around your ear to hear better).

Here is one visual cue of a proper earplug fit: When viewing yourself in a mirror straight ahead (or when looking at a co-worker face-to-face), a poorly-fit earplug is clearly visible protruding from the ear canal, while a properly-fit earplug is hardly visible.

For the user, a good self-test of proper fit of earplugs is easily performed. Prior to inserting your earplugs, press the palms of your hands tightly against your ears, and say some words out loud. Your own voice sounds louder and deeper when your ears are covered. Now insert your earplugs, and repeat that voice check. If the earplugs are properly fit, there will be very little difference in the sound of your voice when you cover and uncover your ears with your hands.

Assumption 3: An earplug halfway in the ear blocks about half the noise.

It seems plausible that if a well-fit earplug blocks 30 dBs of noise, then a half-fit earplug must block 15 dBs of noise. Unfortunately, the math of hearing protection does not work that way. Instead, a half-fit earplug is often providing 0 dBs of attenuation.

Workers in noise levels of 85-95 dBs (close to the OSHA Permissible Exposure Limit of 90 dBs time-weighted average) are routinely offered earplugs with noise reduction ratings (NRRs) of 30 dBs or more. When worn properly, that 30-dB hearing protector can make the worker feel isolated — unable to hear warning signals, co-workers, machine maintenance sounds, or communication radios.

To hear critical sounds, workers will sometimes remove their earplugs about halfway, assuming they are still adequately protected. But in noise attenuation, any small channel or leak allows the noise to enter, and the protection quickly deteriorates from “all” to “none.” How do we protect a worker who does not need 30 dBs of protection? Use hearing protectors with lower NRRs. When used properly, a lower-attenuating earplug will provide protection without sacrificing communication ability.

While there is no magic valve in hearing protectors that lets “good” sound in and keeps “bad” sound out, there are some hearing protectors that are more speech-friendly than others.

Assumption 4. Cut the NRR in half to predict real-world protection.

Since the EPA promulgated its NRRs on all hearing protector packaging in 1974, many studies have shown that attenuation achieved in the real world is sometimes far below the laboratory NRR. There are a number of good reasons for this difference: users in the real-world might not receive proper training, or might adjust their hearing protectors for comfort rather than protection, or they may intentionally compromise the fit in order to hear co-workers and machine noises more clearly.

Using a fit-testing system for earplugs, we visited eight industrial sites and measured real-world attenuation of 100 workers using earplugs from a variety of manufacturers. Workers were instructed to fit their earplugs just the same as they usually do. A personal attenuation rating (PAR) then was measured on each ear. The PAR results showed that one-third of the workers achieved attenuation slightly higher than the published NRR, one-third of workers showed attenuation within 5 dBs below the published NRR, and about one-third showed significantly lower attenuation (anywhere from 0 to 25 dBs).

Recognizing this disparity between real-world and laboratory results, the EPA has announced its intention to update the NRR in the near future. Instead of a single-number attenuation rating (31 dBs, for example), the new NRR label will likely show a two-number range of measured attenuation for a given earplug (18-29 dBs, for example). The lower number indicates the expected attenuation for groups of workers with little or no training, while the higher number represents the expected attenuation for groups of workers with some individual training in hearing protector fitting.

Assumption 5. There's no way to measure real attenuation on a worker wearing earplugs.

There definitely are several methods of measuring real-world attenuation on workers wearing earplugs2. While each method of fit-testing has its own merits, one of the most popular methods is called VeriPRO®. As the name implies, it verifies the protection achieved by a worker wearing earplugs.

In the VeriPRO method, employees are given a special hearing test without their earplugs, and then repeat the test while wearing their right earplug, followed by their left earplug. The difference in the results of these three hearing tests is a measurement of how much protection is being offered by the earplugs, just as they were fit by the worker.

Some workers in the hearing conservation program may achieve a poor fit with the earplugs they are using. In these cases, there are two good options to improve protection:

  1. VeriPRO offers short training videos showing the proper fitting techniques for nearly every style of earplug.

  2. Perhaps a different earplug should be tried.

Assumption 6. There's no way to measure the noise dose of a worker under the hearing protectors throughout the workday.

Ideally, the best way to know if a worker is protected from hazardous noise is to take a noise dosimetry measurement under the hearing protectors — that is, place a microphone at the eardrum. This concept of in-ear dosimetry is now available in a product called QuietDose™.

QuietDose uses dual miniature microphones, each inserted under the earplug or earmuff, to measure the noise dose at the eardrum. This immediate feedback gives the worker (and safety manager) the critical information to make immediate corrections.

Bad assumptions sink many well-intentioned safety initiatives. But avoiding these simple bad assumptions about hearing protection helps a hearing conservation program stay on solid ground, and do just what it is designed to do: prevent noise-induced hearing loss.


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Brad K. Witt is the director of hearing conservation at ISEA member Sperian Hearing Protection, San Diego, Calif. He has a bachelor's degree in communications disorders and a master's in audiology, holds a certificate of clinical competence in audiology, and has served as president of the National Hearing Conservation Association. Witt manages the acoustical laboratory at Sperian, and provides training to professional groups in all aspects of hearing conservation. Reach him at 619-619-1412 or [email protected]

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