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NIOSH Hearing Loss Research Program Review NIOSH Publications on Noise and Hearing The National Academies - Advisors to the Nation on Science, Engineering, and Medicine

What does the HLR Program Do?

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Research Goal 1

Research Goal 2

Research Goal 3

Research Goal 4

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R&D Portfolio - Research Goal 2 : Reduce Hearing Loss through Interventions Targeting Personal Protective Equipment

The HLR program has had a component related to HPDs for more than three decades. Although the NIOSH hierarchy of controls orders engineering and administrative controls ahead of personal protective equipment (PPE), sometimes HPDs are the only practical option for control of noise hazards. For these reasons, one of our research goals is to reduce hearing loss through interventions targeting personal protective equipment, which for noise is HPDs. Our HPD research is coordinated with other goals of the program through planning, information exchange, research teamwork, and information dissemination. One example of this coordination is the publication of a compendium of hearing protectors in 1976, followed by successive updates of that information in 1985, 1995, and 2003 (see Research Goal 1.10). We are currently addressing four issues related to HPDs.

Current methods of rating hearing protector performance do not accurately estimate the protection workers receive. Therefore, one issue we are studying is the method of measurement and rating HPD performance. The HLR program reported the NRR[1] over-estimates real-world protection by 140 percent to 2000 percent.[2], [3] We also found that the type of HPD affected the magnitude of the over-estimate.[4] Based on DOL estimates, 95% of noise-exposed workers had eight-hour exposures of no more than 100 dB(A).[5] When this exposure is compared to the NIOSH REL of 85 dB(A), and the fact that 95% of HPDs can provide 15 dB of attenuation,[6] we know that HPDs have the potential to protect most workers from excessive exposure.

In collaboration with manufacturer, academic, and government laboratories, the HLR program developed a more appropriate method for testing and rating protectors.[7] The method calls for the HPD to be fitted by the test subject rather than an expert. This test standard (adopted by ANSI) is now the basis for testing directives and labeling regulations in Australia, Brazil, Canada and New Zealand.[8],[9],[10],[11] The standard has been formulated as a proposed ISO standard for a naïve subject-fit protocol for hearing protector testing.[12] Furthermore, EPA has commenced revision of their NRR labeling regulation with HLR program staff providing technical oversight (see Research Goal 2.1).

A second issue we are addressing relates to the need to transfer HPD ratings to effective hearing protection for an individual worker on the job. Better test standards and more predictive ratings provide useful population statistics, but are not applicable to the individual worker. NIOSH also recommended that onsite field tests be used to validate the subject-fit protocol specified in the ANSI standard.4 HLR program efforts in this area involve both the development of a laboratory system and a field system for fit-testing HPDs. In a recent HHE, 90 percent of workers who were fit-tested achieved protected noise exposures below 85 dB(A).[13] The HLR program demonstrated that fit-test methods can achieve the same performance as laboratory-based methods.[14]

HLR program scientists developed a laboratory system for testing HPDs and we are working on a comprehensive solution for fit-testing and audiometric screening. The laboratory system has been installed in the NIOSH Cincinnati and Pittsburgh facilities and in the Howard Leight Industries (HLI) testing lab in San Diego. (see Research Goal 2.2)

Another area of HPD research involves understanding the extent to which they protect against impulsive noise. Impulsive noise is known to be more damaging than continuous noise,[15] and the protection afforded by HPDs at high sound pressure levels is not well-known. The EPA’s regulation on labeling states that HPDs may not be effective for noise levels above peak sound pressures of 140 dB.1 OSHA regulations state that workers should not be exposed to peak levels above 140 dB.[16] However, law enforcement and military personnel and workers in the construction and mining sectors often experience impulsive noise exposures above this level. At high sound pressure levels, sound propagation becomes nonlinear not only in air, but also in the material properties of the HPDs themselves. The HLR program developed capabilities to better evaluate the performance of HPDs in the presence of impulse noise. HLR program scientists measured HPD attenuation for gunshot noise stimuli and demonstrated that some earplugs may be protective for only one impulse while others could be protective for 100 rounds fired. Although damage risk criteria are the topic of considerable debate, NIOSH recommends double protection for situations where a worker expects to be exposed to impulses above 140 dB.6 (see Research Goal 2.3)

The HLR program is also studying how to use HPDs to protect hearing-impaired workers. Hearing impaired workers face a dilemma of needing to protect their residual hearing and also needing to communicate[17], [18], [19]  and identify environmental cues and warning signals[20], [21], [22] without additional “impairment” imposed by use of conventional HPDs. However, HPD selection is based upon the worker’s noise exposure and HPD attenuation characteristics without consideration of hearing impairment. Beginning in 2001, HLR program scientists evaluated alternative hearing protection options, such as flat-attenuation HPDs and the use of hearing aids under earmuffs, to determine their utility in alleviating the special problems faced by hearing-impaired workers. From this research we developed a protocol for selecting the HPDs that will maximize speech intelligibility for a hearing-impaired worker while still providing sufficient reduction in noise exposure. The associated field study is currently being conducted as a partnership with General Motors and the UAW. (see Research Goal 2.5)


[1] U.S. Environmental Protection Agency [2004]. CFR Title 40, subchapter G, 211, subpart B—Hearing Protective Devices, U.S. EPA.

[2] Berger EH, Franks JR, Lindgren F [1996]. International review of field studies of hearing protector attenuation. In: Axelsson A, Borchgrevink H, Hamernik RP, Hellstrom L, Henderson D and Salvi RJ, eds. Scientific Basis of Noise-Induced Hearing Loss.New York: Thieme, pp. 361-377.

[3] Berger E H, Franks JR, Behar A, Casali JG, Dixon-Ernst C, Kieper RW, Merry CJ, Mozo BT, Nixon CW, Ohlin D, Royster JD, Royster LH [1998]. Development of a new standard laboratory protocol for estimating the field attenuation of hearing protection devices. Part III. The validity of using subject-fit data. J Acoust Soc Am 103 (2): 665–672.

[4] NIOSH [1998]. Criteria for a Recommended Standard Occupational Noise Exposure: Revised Criteria 1998. U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 98-126.

[5] Franks JR [1988]. “Number of workers exposed to occupational noise.”  Seminars in Hearing 9(4).

[6] Franks JR, Graydon PS, Jeng C, Murphy WJ [2003]. “NIOSH Hearing Protector Device Compendium.” Accessed November 10, 2005.

[7] ANSI S12.6-1997 [2002]. American national standard: Methods for measuring the real-ear attenuation of hearing protectors. New York: American National Standards Institute, Inc., ANSI S12.6-1997.

[8] Australia Standards [2002]. AS/NZS 1270:2002 Acoustics – Hearing protectors.

[9] Brazilian National Association of the Industry of Safety Materials and Work Protection

Technical Standards Personal Protective Equipment Established by Provision 48 of March 25, 2003 of the Ministry of Labor Real Ear Method- Subject fit.

[10] Canadian Standards Association (CSA) Standard Z94.2-02 [2002]. Hearing Protection Devices - Performance, Selection, Care and Use

[11] New Zealand Occupational Safety and Health Service [2001]. Occupational Noise Exposure – Selection and Use of Hearing Protectors.

[12] International Standards Organization [2005]. ISO/CD 4869-75 ISO TC 43/SC 1/WG 17, Acoustics – Hearing Protectors – Part 7: Subject fit method for estimation of noise reduction.

[13] Murphy WJ, Davis RR, Franks JR, Byrne DC. [2005]. NIOSH Health Hazard Evaluation Report: HETA #2004-0095 GM Flint Metal Fabrication Division, Flint, Michigan. U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health March (submitted for internal peer-review Sept. 1, 2005).

[14] Franks JR, Murphy WJ, Harris DA, Johnson JL, Shaw PB [2003]. “Alternative field methods for measuring hearing protector performance.” Am Ind Hyg Assoc J 64(4): 501-509.

[15] Henderson D, Hamernik RP [1986]. Impulse noise: critical review. J Acoust Soc Am 80(2): 569-584.

[16] Occupational Safety and Health Administration [1983]. CPL 2–2.35A–29 CFR 1910.95(b)(1), Guidelines for noise enforcement; Appendix A. Washington DC: U.S. Department of Labor, Occupational Safety and Health Administration, OSHA Directive No. CPL 2–2.35A (December 19, 1983).

[17] Abel SM, Alberti PW, Riko K [1980]. Speech intelligibility in noise with hearing protectors. J Otolaryngology 9(3): 256-265.

[18] Suter AH [1989]. The effects of hearing protectors on speech communication and the perception of warning signals. Technical Memorandum 2-89. US Army Human Engineering Laboratory, Aberdeen Proving Ground, Maryland.

[19] Abel SM, Spencer DL [1997]. Active noise reduction versus conventional hearing protection: Relative benefits for normal hearing and impaired listeners. Scand Audiol 26(3):155-167.

[20] Abel SM, Kunov H, Pichora-Fuller K, Alberti PW [1985]. Signal detection in industrial noise: Effects of noise exposure history, hearing loss, and the use of ear protection. Scand Audiol 14: 161-173.

[21] Abel SM, Hay VH [1996]. Sound localization - The interaction of aging, hearing loss and hearing protection. Scand Audiol 25(1): 3-12.

[22] Zwerling C, Whitten PS, Davis CS, Sprince NL [1997]. Occupational injuries among workers with disabilities - the National Health Interview Survey, 1985-1994. JAMA 278(24): 2163-2166.

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