Participating core and specialty programs: Center for Direct Reading and Sensor Technologies, Engineering Controls, Occupational Health Equity, Prevention through Design, Small Business Assistance, and Surveillance.

Employers, safety professionals, workers, and consensus standard organizations use NIOSH information to reduce noise and ototoxic chemical exposures among manufacturing workers.

  Health Outcome Research Focus Worker Population Research Type
A Hearing loss Develop updated damage/risk recommendations Forge plant workers, as well as others in metal and furniture making subsectors Basic/etiologic
B Hearing loss Develop hearing protection for impulse noise Forge plant, as well as others in metal and furniture making subsectors Intervention
C Hearing loss Understanding the burden of impulse noise Forge plants, as well as others in metal and furniture making Surveillance research
D Hearing Loss Understanding combination of impulse and continuous noise Noise-exposed manufacturing workers Surveillance research
E Hearing Loss Exposure to ototoxic chemicals Manufacturing workers (esp. petroleum and coal products, leather, fiberglass) Surveillance research

Activity Goal 2.3.1 (Basic/Etiologic Research): Conduct basic/etiologic research update damage/risk criteria for impulse noise to reduce hearing loss among manufacturing workers.

Activity Goal 2.3.2 (Intervention Research): Conduct studies to develop and assess the effectiveness of hearing protection interventions for impulse noise to reduce hearing loss among manufacturing workers.

Activity Goal 2.3.3 (Surveillance Research): Conduct surveillance research to develop new tools and methods to better understand the burden of noise overexposure among manufacturing workers.


An estimated prevalence of noise exposed workers in the manufacturing sector is nearly 6 million workers (37%) based upon National Health and Nutrition Examination Survey (NHANES) data [Tak et al. 2009]. To further understand the burden of hearing loss, NIOSH has partnered with hearing conservation providers to collect audiometric data from a broad spectrum of sectors. The burden for hearing loss among noise-exposed workers in the manufacturing sector was about 20% [Masterson et al. 2015]. Noise exposures are typically described as continuous, intermittent and impulsive. Occupational exposure limits have been developed assuming that the exposures are for continuous noise exposures over the course of a lifetime of exposure. Impulsive noise exposures or combinations of continuous noise and impulsive noise pose an increased risk of hearing loss [Davis et al. 2009; Zhao et al. 2010].

Exposures to noise in combination with solvents potentially poses an increased risk of hearing loss because the solvents can affect the auditory system through different mechanisms than the mechanical or metabolic destruction of the sensory hair cells [Johnson and Morata 2010]. The number of workers in the Manufacturing sector that experience mixed exposures is not well known and further surveillance research is needed to characterize the risk.


While the general trend has been one of decline in the incidence of hearing loss in the manufacturing sector (a 2% reduction from 1986–2010), additional research and dissemination efforts are needed [Masterson et al. 2015]. Exposures to impulse noise represent a greater risk for early onset of hearing loss [Zhao et al. 2010; NIOSH 2016] and the interventions to prevent hearing loss from impulse noise have not been assessed for their effectiveness. A better understanding of risk factors (impulse noise, aging, and other agents) is needed. Specific needs include updated guidelines towards these risk factors and the incorporation of new technologies within hearing prevention loss programs, such as the integration of fit testing. A range of new hearing protector technologies has been brought to market in recent years and methods to evaluate their protection against impulse noise is necessary. Among these are devices with Bluetooth™, active noise cancellation, and near field communication capabilities. Research is needed to provide assessment and promotion of new technologies that can affect the field of hearing conservation.

Surveillance research is needed to better characterize noise exposures and hearing loss prevalence, especially among chemical, petroleum, and metal industries within the manufacturing sector. Surveillance research might include using new data sources for surveillance purposes, using existing methods to surveil a new population for which there is limited or no applicable surveillance data, or adding new questions to an existing survey like the National Health Interview Survey that target a population, exposure or outcome. Additionally, workplace noise exposures for targeted Manufacturing Sector tasks should be studied to characterize the noise dose, use/non-use of hearing protection and other personal protective equipment, and assessment of hearing conservation programs.

Employers, workers, hearing conservation providers, health and safety vendors, and safety professionals use NIOSH education tools and resources to prevent harmful noise exposures among manufacturing workers.

NOTE: Goals in bold in the table below are priorities for extramural research.

  Health Outcome Research Focus Worker Population* Research Type
A Hearing loss Integrating new technologies into education (e.g., noise app, fit testing) Noise-exposed manufacturing workers (esp. small businesses) Translation
B Hearing loss Education intervention effectiveness Noise-exposed manufacturing workers (esp. small businesses) Intervention

* See definitions of worker populations

Activity Goal 2.4.1 (Intervention Research): Conduct studies to develop and assess the effectiveness of education interventions to prevent hearing loss among manufacturing workers.

Activity Goal 2.4.2 (Translation Research): Conduct translation research to understand barriers and aids to integrating new technologies into hearing loss prevention education in the manufacturing sector.


Within the manufacturing sector, 22%–55% of workers are exposed to hazardous noise (depending on sub-sector), and between 13% and 39% of these noise-exposed workers report not wearing hearing protection [Tak et al. 2009]. Noise-exposed manufacturing workers in electrical machinery, non-electrical machinery and textiles have the highest prevalence of not using hearing protection [Tak et al. 2009]. Many workers may have an elevated or disproportionate risk, including foreign-born workers and workers with limited English-language skills, workers in small businesses, contingent workers, and younger (teenage) and older (65 and over) workers [Themann et al. 2013].


The 2017 Cochrane systematic review has identified a lack of demonstrated effectiveness for hearing conservation programs with regards to reducing the incidence of noise induced hearing loss [Tikka et al. 2017]. Interventions to prevent hearing loss are sometimes ineffective due to improper and inconsistent use of hearing protection coupled with inadequate training [Voix and Laville 2009; Byrne et al. 2017]. Employers and workers would benefit from education about noise, including the proper way to insert foam ear plugs, “Buy Quiet” programs, ways to reduce vibration of equipment to possibly reduce noise, and use of administrative controls to limit exposure to hazardous noise, as specified by OSHA requirements that allow for various exposure time/noise intensity levels [OSHA 2011].

Some hearing protection manufacturers now provide hearing protector fit-testing systems that can measure a Personal Attenuation Rating of hearing protectors which provide opportunities to aid in the proper selection of hearing protection. Translational research for fit testing methods is needed. In addition, hearing protection researchers and advocates should communicate with employers and employees about new smartphone-based noise metering apps [Kardous and Shaw 2015; Roberts et al. 2016]. Use of these tools will create an awareness of noise exposures, leading to steps to limit or reduce exposure to noise hazards.

Byrne DC, Murphy WJ, Krieg EF, Ghent RM, Michael KL, Stefanson EW, Ahroon WA [2017]. Inter-laboratory comparison of three earplug fit-test systems, J Occup Environ Hyg 14(4), 294-305 DOI: 10.1080/15459624.2016.1250002.

NIOSH [2016]. Evaluation of impact and continuous noise exposure, hearing loss, heat stress, and whole body vibration at a hammer forge. By Brueck SE, Eisenberg, J, Zechmann EL, Murphy WJ, Morata TC, Krieg EF. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Health and Safety, Health Hazard Evaluation Report 2007-0075-3251,

Davis RI, Qiu W, Hamernik RP [2009]. The role of the kurtosis statistic in evaluating complex noise exposures for the protection of hearing. Ear Hear, 30:628–634.

Johnson AC, Morata TC [2010]. Occupational exposure to chemicals and hearing impairment. The Nordic Expert Group for Criteria Documentation of Health Risks from Chemicals 44(4):1-177.

Kardous C, Shaw P [2014]. Evaluation of smartphone sound measurement applications, J Acoust Soc Am 135: EL186–EL192.

Masterson EA, Deddens JA, Themann CL, Bertke S, Calvert GM [2015]. Trends in worker hearing loss by industry sector, 1981-2010. Am J Ind Med 58:392-401.

OSHA [2011]. 29 CFR 1910.95 Occupational noise exposure. Washington, DC: U.S. Department of Labor, Occupational Safety and Health Administration,

Roberts B, Kardous C, Neitzel R [2016]. Improving the accuracy of smart devices to measure noise exposure. J Occup Environ Hyg 13(11), 840-846, DOI: 10.1080/15459624.2016.1183014.

Tak S, Davis RR, Calvert GM [2009]. Exposure to hazardous workplace noise and use of hearing protection devices among US workers — NHANES, 1999-2004. Am J Ind Med 52(5):358-371.

Themann CL, Suter AH, Stephenson MR [2013]. National research agenda for the prevention of occupational hearing loss – part 2. Sem Hear 34(3):208-251.

Voix J, Laville F [2009]. The objective measurement of individual earplug field performance. J Acoust Soc Am 125(6) 3722-3732.

Zhao YM, Qiu W Zeng L, Chen SS, Cheng XR, Davis RI, Hamernik RP [2010]. Application of the kurtosis statistic to the evaluation of the risk of hearing loss in workers exposed to high-level complex noise Ear Hear 31:527-532.

Page last reviewed: April 24, 2018