Chapter 6. Hearing Protectors

A personal hearing protection device (or hearing protector) is any device designed to reduce the level of sound reaching the eardrum. Earmuffs, earplugs, and ear canal caps (also called semi-inserts) are the main types of hearing protectors. A wide range of hearing protectors exists within each of these categories. For example, earplugs may be subcategorized into foam, user-formable (such as silicon or spun mineral fiber), premolded, and custom-molded earplugs. In addition, some types of helmets (in particular, flight helmets worn in the military) also function as hearing protectors. Refer to Nixon and Berger [1991] for a detailed discussion of the uses, advantages, and disadvantages of each type of protector. Items not specifically designed to serve as hearing protectors (e.g., cigarette filters, cotton, and .38-caliber shells) should not be used in place of hearing protectors. Likewise, devices such as hearing aid earmolds, swim molds, and personal stereo earphones must never be considered as being hearing protective.

Ideally, the most effective way to prevent NIHL is to remove the hazardous noise from the workplace or to remove the worker from the hazardous noise. Hearing protectors should be used when engineering controls and work practices are not feasible for reducing noise exposures to safe levels. In some cases, hearing protectors are an interim solution to noise exposure. In other instances, hearing protectors may be the only feasible means of protecting the worker. When a worker's time-weighted noise exposure exceeds 100 dBA, both earplugs and earmuffs should be worn. It is important to note that using such double protection will add only 5 to 10 dB of attenuation [Nixon and Berger 1991]. Given the real-world performance of hearing protectors [Berger et al. 1996], NIOSH cautions that even double protection is inadequate when TWA exposures exceed 105dBA.

How much attenuation a hearing protector provides depends on its characteristics and how the worker wears it. The selected hearing protector must be capable of keeping the noise exposure at the ear below 85 dBA. Because a worker may not know how long a given noise exposure will last or what additional noise exposure he or she may incur later in the day, it may be prudent to wear hearing protectors whenever working in hazardous noise. Workers and supervisors should periodically ensure that the hearing protectors are worn correctly, are fitted properly, and are appropriate for the noise in which they are worn [Helmkamp et al. 1984; Gasaway 1985; Berger 1986; Royster and Royster 1990; NIOSH 1996].

Historically, emphasis has been placed on a hearing protector's attenuation characteristics—almost to the exclusion of other qualities necessary for it to be effective. Although those who select hearing protectors should consider the noise in which they will be worn, they must also consider the workers who will be wearing them, the need for compatibility with other safety equipment, and workplace conditions such as temperature, humidity, and atmospheric pressure [Gasaway 1985; Berger 1986]. In addition, a variety of styles should be provided so that workers may select a hearing protector on the basis of comfort, ease of use and handling, and impact on communication [NIOSH 1996; Royster and Royster 1990]. Each worker should receive individual training in the selection, fitting, use, repair, and replacement of the hearing protector [Gasaway 1985; Royster and Royster 1990; NIOSH 1996]. What is the best hearing protector for some

workers may not be the best for others [Casali and Park 1990]. The most common excuses reported by workers for not wearing hearing protectors include discomfort, interference with hearing speech and warning signals, and the belief that workers have no control over an inevitable process that culminates in hearing loss [Berger 1980; Helmkamp 1986; Lusk et al. 1993]. Fortunately, none of these reasons present insurmountable barriers. Given adequate education and training, each can be successfully addressed [Lusk et al. 1995; Merry 1996; Stephenson 1996].

Workers and management must recognize the crucial importance of wearing hearing protectors correctly. Intermittent wear will dramatically reduce their effective protection [NIOSH 1996]. For example, a hearing protector that could optimally provide 30dB of attenuation for an 8-hr exposure would effectively provide only 15 dB if the worker removed the device for a cumulative 30 min during an 8-hr day. The best hearing protector is the one that the worker will wear.

Several methods exist for estimating the amount of sound attenuation a hearing protector provides. In the United States, the NRR is required by law [40 CFR 211] to be shown on the label of each hearing protector sold. The NRR was designed to function as a simplified descriptor of the amount of protection provided by a given device. When its use was first proposed, the most typical method used to characterize sound attenuation was the real ear attenuation at threshold (REAT) method, as described in ANSI S3.19-1974 [ANSI 1974]. Sometimes called the octave-band or long method, this method was believed to provide too much information to be useful for labeling purposes; thus a single-number descriptor (NRR) was devised.

The formulas used to calculate the NRR are based on the octave-band, experimenter fit, REAT method. The NRR was intended to be used to calculate the exposure under the hearing protector by subtracting the NRR from the C-weighted unprotected noise level. It is important to note that when working with A-weighted noise levels, one must subtract an additional 7 dB from the labeled NRR to obtain an estimate of the A-weighted noise level under the protector. OSHA has prescribed six methods^* with which the NRR can be used. (See 29 CFR 1910.95, Appendix B, and descriptions of methods for calculating and using the NRR in The NIOSH Compendium of Hearing Protection Devices [NIOSH 1994].)

* The OSHA methods are a simplification of NIOSH methods #2 and #3 [NIOSH 1975, 1994; Lempert 1984].

One problem inherent to using single-number descriptors of sound attenuation is the need to ensure that the resulting value does not sacrifice the estimated protection for the sake of simplicity. Thus these calculations will typically underestimate laboratory-derived "long methods" for estimating sound attenuation. To get around some of the limitations associated with NRR calculations, other methods have been developed for estimating hearing protector performance. The single-number rating method and the high-middle-low method may be used when a person needs to estimate performance more accurately than possible with the NRR but does not want to resort to octave-band descriptions of sound attenuation. Detailed descriptions of these methods are in The NIOSH Compendium of Hearing Protection Devices [NIOSH 1994].

Both NRR and the other hearing protector ratings referred to above are based on data obtained under laboratory conditions in which experimenters fit hearing protectors on trained listeners. As such, these ratings may differ markedly from the noise reduction that a worker would actually experience in the real world. Specifically, studies have repeatedly demonstrated that real-world protection is substantially less than noise attenuation values derived from experimenter-fit, laboratory-based methods. In the late 1970's and early 1980's, two NIOSH field studies found that insert-type hearing protectors in the field provided less than half the noise attenuation measured in the laboratory [Edwards et al. 1979; Lempert and Edwards 1983]. Since the 1970's, additional studies have been conducted on real-world noise attenuation with hearing protectors [Regan 1975; Padilla 1976; Abel et al. 1978; Edwards et al. 1978; Fleming 1980; Crawford and Nozza 1981; Chung et al. 1983; Hachey and Roberts 1983; Royster et al. 1984; Behar 1985; Mendez et al. 1986; Smoorenburg et al. 1986; Edwards and Green 1987; Pekkarinen 1987; Pfeiffer et al. 1989; Hempstock and Hill 1990; Berger and Kieper 1991; Casali and Park 1991; Durkt 1993]. In general, these studies involved testing the hearing thresholds of occluded and unoccluded ears of subjects who wore the hearing protectors for the test in the same manner as on the job. The tests attempted to simulate the actual conditions in which hearing protectors are normally used in the workplace. Table 6-1 compares the NRRs derived from these real-world noise attenuation data with the manufacturers' labeled NRRs or laboratory NRRs. The laboratory NRRs consistently overestimated the real-world NRRs by 140% to 2,000% [Berger etal. 1996]. In general, the data show that earmuffs provide the highest real-world noise attenuation values, followed by foam earplugs; all other insert-type devices provide the least attenuation. From these results, it can also be concluded that ideally, workers should be individually fit-tested for hearing protectors. Currently, several laboratories are exploring feasible methods for this type of fit testing [Michael 1997].

Royster et al. [1996] addressed problems associated with the use of the NRR. These researchers demonstrated that relying on the manufacturer's instructions or the experimenter to fit hearing protectors may be of little value in estimating the protection a worker obtains under conditions of actual use. The Royster et al. [1996] study reported the results of an interlaboratory investigation of methods for assessing hearing protector performance. The results demonstrated that using untrained subjects to fit their hearing protectors provided much better estimates of the hearing protector's noise attenuation in the workplace than using the experimenter to fit them. This method has since been adopted for use by ANSI in ANSI S12.6-1997 [ANSI 1997]. Furthermore, the method has subsequently been endorsed by the NHCA Task Force on Hearing Protector Effectiveness as well as numerous other professional organizations.^†

^†The following organizations have endorsed the use of the subject fit procedure according to ANSI S12.6: Acoustical Society of America, American Academy of Audiology, American Association of Occupational Health Nurses, American Industrial Hygiene Association (AIHA), American Society of Safety Engineers, ASHA, CAOHC, and NHCA.

OSHA [1983] has instructed its compliance officers to derate the NRR by 50% in enforcing the engineering control provision of the OSHA noise standard. However, NIOSH concurs with the professional organizations cited above and recommends using subject fit data based on ANSI S12.6-1997 [ANSI 1997] to estimate hearing protector noise attenuation. If subject fit data are not available, NIOSH recommends derating hearing protectors by a factor that corresponds to the available real-world data. Specifically, NIOSH recommends that the labeled NRRs be derated as follows:

For example, measure noise exposure levels in dBC or dBA with a sound level meter or noise dosimeter.

To summarize, the best hearing protection for any worker is the removal of hazardous noise from the workplace. Until that happens, the best hearing protector for a worker is the one he or she will wear willingly and consistently. The following factors are extremely important determinants of worker acceptance of hearing protectors and the likelihood that workers will wear them consistently:

• Convenience and availability
• Belief that the device can be worn correctly
• Belief that the device will prevent hearing loss
• Belief that the device will not impair a workers ability to hear important sounds
• Comfort
• Adequate noise reduction
• Ease of fit
• Compatibility with other personal protective equipment