Hearing Loss in the Mining Industry: 

Overview of the NIOSH Hearing Loss Prevention 

Program at the Pittsburgh Research Laboratory 

R.J. Matetic 
 

Abstract 

The National Institute for Occupational Safety and Health (NIOSH) 

has recognized that Noise-Induced Hearing Loss (NIHL) is the most 

common occupational illness in the United States. The use of heavy 

equipment, the drilling of rock, and the confined work environment are 

some of the factors that contribute to high levels of noise exposure to 

workers in the mining industry. Every day 80% of the nation’s miners 

go to work in an environment where the time weighted average 

(TWA) exceeds 85 dBA. Moreover, 25% of the miners are exposed to 

a TWA noise level that exceeds 90 dBA, the Permissible Exposure Limit 

(PEL). Furthermore, a NIOSH analysis of a large sample of audiograms 

showed that at age 50 approximately 90% of coal miners and 49% 

of metal/non-metal miners have a hearing impairment. By contrast, 

only 10% of the non-occupational-noise exposed population has a 

hearing impairment at age 50 (Franks, 1997) (Stephenson, 1998). 

Simply stated, the majority of miners have a hearing loss by the time 

they retire. While NIHL is the most common occupational disease in 

this country, this problem is especially acute among workers in the 

mining industry. There are several barriers to reducing NIHL in the 

mining industry. These include: gaps in knowledge of noise dose/source 

relationships, the unavailability of effective noise controls, and needs 

for worker education and worker empowerment. A related issue is 

the difficulty of communication in noisy workplaces by both hearing 

impaired and normal hearing workers. The Pittsburgh Research 

Laboratory (PRL) at NIOSH has strategically developed a hearing loss 

prevention program for overcoming these respective barriers in an 

attempt to reduce NIHL in the mining industry. This paper provides an 

overview of the research program being conducted at the PRL. 

Hearing Loss Program Methodology 

The hearing loss research program at the NIOSH-PRL, Hearing Loss 

Prevention Branch (HLPB) is comprised of four key programmatic areas. 

These areas are: 1) noise dose/source relationships; 2) availability of 

effective noise controls; 3) worker education and empowerment and 4) 

communication issues. The methodology for selection of the program 

areas includes the following: 

Noise dose/source relationships: The mining industry does not 

dedicate the resources in determining where workers receive their 

noise exposures. Knowledge of the noise source/exposure relationship 

allows for effective selection and implementation of noise controls, thus 

reducing NIHL within the mining population. 

Availability of effective noise controls: In many cases, attempts at 

reducing sound levels with noise controls are unsuccessful in the mining 

industry due to misapplication of technologies, lack of maintenance of 

noise controls used on equipment and/or treating noise sources that 

are insignificant in terms of a worker’s exposure. In other cases, noise 

controls have not been developed due to the lack of understanding of 

the mechanisms of noise generation or the inability to develop controls 

that have suitable durability in the mining environment. 

Worker empowerment and education: Workers report that 

they are rarely included or consulted in hearing conservation efforts. 

However, their involvement is crucial for the effective deployment 

of most exposure reduction strategies. Workers need to have better 

information about the noise hazards in their workplaces and how much 

actual exposure they are receiving from these sources. They also need 

to be empowered with techniques to reduce their exposure by playing 

a greater part in the overall hearing conservation effort. Additionally, 

workers typically receive inadequate education on what they can do 

to conserve their hearing. Common problems include training that is 

sporadic and uninteresting, little feedback on whether the training 

actually increased their knowledge or skills, and an overemphasis on 

hearing protection at the expense of the many other strategies workers 

can utilize to reduce their own exposures. 

Communication issues: In mines and other noisy settings, workers 

report a significant problem with hearing warning signals, speech, and 

other sounds that are critical to working safely and efficiently. This 

problem is exacerbated by the masking nature of background noise, the 

high prevalence of hearing impairment, and the over reliance on simple 

hearing protection to reduce exposures. 

The hearing loss program at the PRL is reducing NIHL in the mining 

industry by addressing the above key programmatic areas. 

All programmatic areas are providing research results in a combined 

effort to reduce NIHL in the mining industry. Figure 1 demonstrates 

how each programmatic area contributes to the overall goal of the 

hearing loss program. 

Figure 1. Programmatic areas and their association with the hearing loss 

prevention program. 

The following section describes the purpose and approach of each 

programmatic area, along with recent results contributing to the overall 

goal of the hearing loss program, which is reducing NIHL in the 

mining industry. 

Hearing Loss Programmatic Areas 

Develop and maintain a noise source/mine worker exposure 

database for prioritizing noise control technologies 

Purpose: The purpose of this programmatic area is to build a 

database that contains up-to-date comprehensive profiles of the 

noise exposures to the mining population as a function of equipment 

and activity-specific measures, i.e., to define the noise source/worker 

dose relationship. It combines the efforts of past research studies 

with current worker noise exposure characterization studies and 

equipment/activity related noise data. This study is a crucial component 

in NIOSH’s and the mining industry’s efforts to develop engineering 

and administrative noise controls because it will define miners’ noise 

exposures, the source of the exposures, and the characteristics of those 

sources. Once this information is available, efforts can then be focused 

on the development and application of appropriate control measures to 

reduce mine worker’s exposures and NIHL in the mining industry. 

Approach: A cross-sectional field study of the noise exposure of 

mine workers is being conducted; the study includes a variety of mining 

methods, equipment, a range of geographic locations, and different 

mine sizes. Surface and underground coal mines, coal preparation 

plants, metal/nonmetal mines, stone mines, and sand & gravel 

operations are included in the study. To establish representative noise 

exposure profiles for the various mining occupations, comprehensive 

and extensive noise exposure measurements are being completed 

(figure 2). Full-shift time-resolved dosimetry, task observations, and 

equipment/area noise profiles are being used to define the noise 

source/worker dose relationships. The basic idea is to establish typical 

exposure patterns for the different mining occupations through 

repeated sampling with the dosimetric instrumentation, then through 

observational data, relate exposures to sources. Finally, sound level 

measurements including frequency analyses will be used to characterize 

the specific noise sources responsible for worker noise exposures. 

Results: To date, 37 site specific surveys have been completed that 

included eight underground coal mines, eleven surface coal mines, nine 

coal preparation plants, three surface stone mines, three underground 

stone mines, one underground silver/lead mine, one coal load out river 

facility, and one sand & gravel operation. In the coal mining sector, 

approximately 40% of the workers surveyed had exposures above 

the MSHA (Mine Safety and Health Administration) PEL (Permissible 
Exposure Limit) of 100% or a time-weighted average of 90 dBA over 

an 8-hour period (TWA8

), resulting from operating equipment such as 

continuous mining machines, roof bolting machines, longwall shearers 

and stage loaders, and working in the dragline house and in and 

around preparation plant equipment. In the stone and sand and gravel 

industries, fewer than 10% of all workers surveyed experienced noise 

exposures above the MSHA PEL of 100%. 

The MSHA rule (30 CFR 62) mandates the mine operator assure that 

no miner is exposed during any work shift to noise that exceeds the 

PEL (based on a 90-dB criterion level, 5-dB exchange rate, A-weighting 

and slow response). If during any work shift a miner’s noise exposure 

exceeds the PEL, the mine operator must use all feasible engineering 

and administrative controls to the reduce the miner’s noise exposure to 

the PEL, and enroll the miner in a hearing conservation program. 

Figure 2. Contour plot of sound levels around a longwall stage loader. 

Development and Assessment of Noise Controls 

Purpose: The strategy for the noise control research program area 

is a long-term implementation plan where appropriate engineering 

controls are selected and targeted to reduce excessive exposure to noise 

and prevent additional cases of NIHL in the mining population. 

The quiet-by-design approach for noise control is emphasized, but lowcost retrofit of equipment with noise control measures is also 

a component. 

Approach (Assessment of Controls): The noise control research 

program has two parts: The first is to determine the availability of 

effective noise controls. In many cases attempts at reducing sound 

levels with noise controls are unsuccessful due to misapplication of 

technologies, lack of maintenance of noise controls or focusing on 

the noise source that is insignificant towards reducing the workers’ 

exposure. Noise surveys are conducted on available noise controls at 

mine sites and are assessed for effectiveness. The methodology for the 

assessment of engineering noise controls can be broken down into 

five areas: 

1) identification of machines with installed engineering noise 

controls; 2) development of a test plan dependent upon the type 

of machine and the type of engineering noise control installed; 3) 

evaluation of the installed control or controls utilizing sound level, 

sound intensity and dosimetric measurements; 4) analysis of the 

experimental results to determine the effect of the controls on the 

sound level at the equipment operator’s ear and/or the operator’s 

noise exposure and 5) dissemination of the information via reports, 

presentations, peer-reviewed publications, or handbooks. 

Results: Findings to date show that engineering noise controls that 

work on the surface may not work as well as expected underground; 

properly installed barriers provide effective noise reduction; improperly 

placed absorptive material has little to no effect on sound levels; and a 

noise problem should be verified before a solution is attempted. 

Approach (Development of Controls): The second part of the 

noise control research program is the development of noise controls. 

In many cases, noise controls have not been developed due to the 

lack of understanding on how the noise is generated or the inability 

to develop a noise control that is durable in the mining environment. 

The methodology for the development of noise controls conducted at 

NIOSH is broken down into seven areas, which include: 

1) identification and rank order of dominant noise sources utilizing 

sound power, sound level and sound intensity measurements in a 

laboratory setting (controlled environment); 2) process and analyze 

laboratory data to determine the areas of the machine that are 

dominant contributors to radiated noise; 3) propose and evaluate 

noise controls that address the dominant noise sources based on their 

potential to reduce noise, cost, functionality, ease of implementation, 

durability and worker acceptance; 4) coordinate with equipment 

manufacturers and users during the process of data collection and 

analysis to assess the feasibility of the controls prior to selecting the 

best noise control concepts; 5) design, implement and laboratory test 

the proposed noise controls to design functional noise controls based 

on the highest rated noise control concepts; 6) implement and test 

noise controls (before and after installation) in a mining environment 

utilizing sound level and dosimetric measurements to determine 

sound level and exposure reduction over a period of time (3-month 

intervals for a 1-yr period). In addition, inspect the condition of the 

controls over the 1-yr period for worker acceptance and durability 

and 7) disseminate results of the research via appropriate conferences, 

meetings, peer-reviewed journal articles and other publications. 

Results (Development of controls): The current focus by NIOSH is 

developing engineering noise controls for continuous mining machines, 

roof bolting machines, and surface drills. The Continuous mining 

machine is first among all the equipment in underground coal whose 

operators exceed 100% noise dosage. NIOSH has addressed this issue 

by developing a chain conveyor with coated flights as a noise control 

for reducing the sound power of continuous mining machines (figure 

3). The coating has been shown to be very durable. A total reduction 

of 7dB A-weighted at the operator position has been achieved with 

the coating. The control is currently being manufactured by Joy 

Manufacturing. Joy Manufacturing represents the largest producer of 

continuous mining machines in the U.S and the coated flight chain 

conveyor noise control is currently in use in several mines. 

Figure 3. Coated flight bars on a continuous mining machine in an 

underground coal mine. 

Roof bolting machine operators are the third most likely to be 

overexposed to noise and rank second when considering only the 

equipment used in underground coal mining. NIOSH has confirmed that 

during wet drilling, sound power level emissions are less than similar 

tests conducted under vacuum conditions of the roof bolting machine. 

This is primarily due to attenuating the sound power emission at 

frequencies of 1 kHz or greater. Wet drilling also facilitates the 

additional benefit of increased performance such as higher penetration 

rates and extended bit life. Roof bolting machines equipped for wet 

drilling are currently available from Fletcher Mining Equipment, the 

leading manufacturer of roof bolting machines in the U.S. NIOSH has 

also confirmed that mist sound power level emissions during mist 

drilling are less than similar tests conducted under vacuum conditions. 

Again, there is the reduction of the noise emissions at 1 kHz and above 

as well as the increase in performance. Depending on the compressive 

strength of the drill media, laboratory and field testing suggest sound 
level reductions of 2-7 dB A-weighted at the operator’s position. Mist 

systems developed by Joy Mining Machinery for roof bolting machines 

are currently in use in several underground coal mines. 

Additionally, NIOSH has confirmed that surface drill operators 

at mine and construction sites experience overexposure to noise. 

NIOSH has addressed this issue by developing a partial cab as a noise 

control for reducing the noise generated from surface drills (figure 

4). Laboratory test results of the partial cab’s configuration and 

material content design showed an 8 to 15 dB A-weighted sound 

level attenuation. Preliminary test results of the proto-type partial cab, 

fabricated and attached to a production air rotary drill rig, indicate 

sound level attenuations of 8 dB A-weighted. Future partial cab 

modification designs based on field applications expect to improve 

sound level attenuations to 10 dB or greater at the operator’s 

control panel. 

Figure 4. Partial cab installed on an air-rotary drilling rig. 

To test and develop noise controls, the NIOSH-PRL has several key 

facilities available for researchers to conduct laboratory testing of the 

controls. These facilities consist of the following: 

Mining Equipment Test Facility – This facility provides fullscale surface testing of mining equipment in an essentially free field 

environment prior to taking equipment underground for testing in the 

actual mine environment. The building complex consists of an open 

high-bay facility that is more that 4200 square meters in a free 

field area. 

Reverberation Room – This room was designed for sound power 

testing of large mining equipment in conformance with ISO standard 

3741. The room is18.31 meters long by 10.38 meters wide by 6.72 

meters high, which yields an interior volume of 1277 cubic meters and 

a surface area of 766 square meters, the largest such facility in North 

America (figure 5). The reverberation room is equipped with a sound 

measurement system which includes an array of 15 microphones that 

are suspended from the ceiling of the reverberation room and an 

instrumentation system for calculating sound power levels. 

Figure 5. Continuous mining machine in the reverberation room at the 

NIOSH-PRL. 

Worker Empowerment and Education 

Purpose: The worker empowerment program area at NIOSH is 

supporting workers as key players in the overall strategy to reduce 

NIHL. Almost every approach to hearing loss prevention has some 

human component. Engineering noise controls usually rely on workers 

to properly implement, use, and maintain them. Administrative controls 

are effective only if workers follow their dictates. Hearing protectors 

only work if they are worn correctly whenever the worker is exposed 

to hazardous noise. 

The worker empowerment program provides outputs that will have 

a direct effect on the overexposure problem as well as internal inputs 

and outputs to the other programs. The direct outputs take the form 

of “Research to Practice” (r2p) products. These are products based on 

technical, engineering, and scientific work that have been translated 

into a form that can be directly used by workers. For instance, workers 

are unlikely to read through lengthy technical reports about noise 

dosimetry, but they would be much more likely to use simplified 

guidelines about how to identify and avoid major noise sources. 

Initially, this program has concentrated on first motivating workers 

and managers to prevent hearing loss. Once motivation levels are 

raised, the next step is to address specific prevention behaviors. The 

first prevention behavior addressed in this program is effective use of 

hearing protectors. Even when hearing protectors are required, actual 

usage rates are low. For instance, Landen (2004) reported that 47.6% 

of a sample of sand and gravel miners never wore hearing protectors. 

Even when hearing protectors are worn, the actual levels of 

protection tend to be far below the rated performance (Berger, Franks, 

and Lindgren, 1994). The solution is a combination of improved 

motivation to perform the task correctly, and improved ability for 

performing the task. 

Approach: This program uses the behavioral sciences to effect 

change. The theoretical basis incorporates aspects of major health 

promotion motivation theories such as Pender’s (1987) Health 

Promotion Model and Ajzen’s (1991) Theory of Planned Behavior. 

Using these theories, communication products are designed to 

emphasize both the likelihood of and severity of noise-induced hearing 

loss. The program also incorporates concepts from the Transtheoretical 

Stages of Change model (Prochaska & DiClemente, 1992) to tailor the 

design of different types of communication interventions. For instance, 

workers who do not yet recognize a problem need different types of 

information than those who are actively seeking a solution. 

Results: The NIOSH Hearing Loss Simulator is a motivational tool 

developed to show both the likelihood and severity of hearing loss. 

The Simulator is a software program that allows users to see and hear 

the effects of hazardous noise exposure. A display and on-screen 

controls allow the user to select different sound levels and durations, 

then instantly hear the effect on pre-recorded speech sounds with or 
 

without background noise (figure 6). The simulated noise-induced 

hearing loss follows the empirically-supported models in ANSI S3.44 

(2001). As a prototype communication product, the Simulator was 

evaluated with groups of miners and mine technical support personnel. 

The initial version was readily adaptable to different media to address 

different trainee and user populations (Randolph, Kohler, and 

Byrne, 2002). 

Figure 6. NIOSH-PRL hearing loss simulator. 

The problem of improper wearing of hearing protectors was 

addressed through a simplified earplug technique. Called the “Roll-PullHold” technique, it emphasizes the three critical actions that must be 

performed to obtain a high level of protection from earplugs. 

The existing instructions printed on earplug packaging or contained 

in training videos are complex and verbose, and the essential message 

is easily missed. In particular, the second step of earplug insertion is 

typically labeled as “Insert” with little emphasis on the technique of 

pulling the outer ear upward to straighten the ear canal. Since the label 

“Insert” is obvious to the point of uselessness, this step was relabeled 

“Pull” to highlight the often forgotten upward pull technique. This 

technique was evaluated with miners who received different forms of 

the Roll-Pull-Hold training along with hearing tests 

Results: Evaluations of the Hearing Loss Simulator showed positive 

reactions to it as an appealing training product. More importantly, 

trainees showed positive changes in the specific attitudes and beliefs 

targeted by the Simulator. The differences in pre- and post-training 

responses indicated that all of the changes were in the desired 

direction, except for responses about hearing loss and age. The 

Simulator has now been released to the public, and is available as a 

download from www.cdc.gov/niosh and on CD-ROM on request to 

rrandolph@cdc.gov. 

The simplified Roll-Pull-Hold technique also yielded significant 

prevention results. Initial testing showed that, while 96% of the tested 

miners correctly performed the Roll step, only 54% correctly performed 

the Pull step and 49% performed the Hold step. When all three steps 

were performed correctly, measured protection rose by over nine 

decibels (figure 7). Information about the Roll-Pull-Hold technique, 

including a 30-second video, can be accessed on the NIOSH website at 

www.cdc.gov/niosh/mining/topics/hearing/earplug.html. 

Communication and Hearing Protectors 

Purpose: Hearing protectors are indispensable in situations 

where noise cannot be sufficiently reduced though engineering and 

administrative controls. However, conventional hearing protectors have 

significant drawbacks that present challenges to their usefulness. For 

instance, while conventional hearing protectors attenuate undesirable 

noise, they can also reduce the audibility of speech, warning signals, 

and other useful sounds (Suter, 1989). Comfort, usability, and 

interference with the wearer’s other tasks also present significant 

barriers to consistent hearing protector use. This program area is 

addressing these hearing protector drawbacks through a combination 

of improved selection methods and evaluation of novel technologies. 

Workers receive information through a variety of sounds, some 

of which are relatively common and generic, while others are very 

task-specific. Spoken communication is the most common type of 

information-bearing sound in both occupational and non-occupational 

settings, so most of the hearing protector audibility research has 

focused on speech recognition. Workers in mines and other industrial 

settings also need to be able to hear backup alarms and other 

warning signals that may be rare outside of the workplace. Equipment 

operators report that they listen for subtle changes in the sounds from 

their machines to monitor their performance and predict mechanical 

problems. In all of these cases, the goal is to preserve audibility of 

essential information-bearing sounds while reducing exposure to noise. 

While there are standard methods of rating the attenuation of hearing 

protectors (e.g., ANSI, 1997), there is no standard for rating the effect 

on speech intelligibility or audibility of warnings. 

The benefit from this program area comes in the form of improved 

hearing protector technologies, and better selection processes for 

choosing the protectors that are available. Choosing appropriate 

hearing protectors is a significant problem. Hundreds of different 

varieties of hearing protectors are currently available. The current 

NIOSH Compendium of Hearing Protectors (online at www.cdc.gov/ 

niosh/topics/noise/hpcomp.html) contained 369 earmuffs, earplugs, 

canal caps, and other devices. 

Approach: In this program area, HPD’s are subjected to laboratory 

evaluations to assess their audibility performance as well as any novel 

features they have. Basic attenuation performance is assessed according 

to ANSI 12.6 and other existing standards. Audibility is assessed 

through experiments in the PRL Auditory Research Laboratory using 

recordings of speech sounds as well as a wide variety of mining and 

industrial sounds presented to volunteer human subjects. When the 

intelligibility and audibility experiments are completed, the data will be 

used to develop an improved hearing protector selection tool. This tool 

will complement the existing NIOSH Compendium of Hearing Protectors 

by providing situation-specific hearing protector recommendations. 

Results: This research program is relatively new, and most of the 

studies hae just started. Special evaluations can be conducted to 

evaluate special features incorporated into hearing protectors. For 

instance, one new hearing protector system incorporated exposuremeasuring microphones into the protectors. The readings produced by 

these microphones were compared to standard dosimeter microphones 

worn on a worker’s shoulders and a “gold standard” high-precision 

microphone located at the center-of-head position. The study on 

the new hearing protectors that also measure noise exposure found 

that the system’s microphones could provide a useful estimate of the 

dose received. The system showed some discrepancies from both the 

standard dosimeter microphones and a center-of-head microphone, 

but these differences tended to be in a conservative direction. That is, 

where errors existed, the system indicated higher sound levels than the 

comparison microphones. 

Figure 7. Evaluation of roll-pull-hold technique. 
Summary 

NIOSH has strategically developed a hearing loss prevention program 

for overcoming respective hearing loss barriers in an attempt to reduce 

NIHL in the mining industry. Thru the utilization of a well-balanced 

research approach, consisting of four key programmatic areas, 

research is being conducted and findings are being implemented and 

disseminated to the mining industry. The long-term impact of these 

and other successful interventions will be followed through long term 

evaluations to confirm that workers are being exposed to less noise and 

that fewer of them will develop a hearing loss. 

It should also be noted that NIOSH has been working under a 

Coal Noise Partnership with the United Mine Workers of America, 

Bituminous Coal Operators Association, National Mining Association, 

Mine Safety and Health Administration and several mining equipment 

manufacturers and suppliers. The partnership is providing opportunities 

for collaborative research with key stakeholders (mine operators, labor 

officials, equipment manufacturers, regulatory officials, etc.) related to 

the hearing loss prevention program at the Pittsburgh Laboratory (PRL). 

The partnership is providing a significant impact in accomplishing the 

goals of the hearing loss prevention program. 

References: 

Ajzen, I. (1991). The theory of planned behavior. Organizational 

behavior and human decision processes, 50, 179-211. 

American National Standards Institute. (2001). Determination of 

occupational noise exposure and estimation of noise-induced hearing 

impairment. (ANSI S3.44-1996, R2001). New York, ANSI. 

American National Standards Institute. (1997). Methods for 

measuring the real ear attenuation of hearing protectors. (ANSI S12.6 

1997). New York, ANSI. 

Berger EH, Franks JR, Lindgren F. (1994) International review of 

field studies of hearing protector attenuation. Proceedings of the 

5th International Symposium on the Effects of Noise on Hearing. 

Gothenburg, Sweden. 

Code of Federal Regulations, Title 30, Part 62. Occupational 

Noise Exposure. Department of Labor, Mine Safety and Health 

Administration. 

International Organization for Standardization. ISO 3741, Acoustics 

– Determination of sound power levels of noise sources – Precision 

methods for reverberation rooms. 

National Institute for Occupational Safety and Health (NIOSH): 

Analysis of audiograms for a large cohort of noise-exposed miners. 

Franks, J.R., pp. 1-7. 

National Institute for Occupational Safety and Health (NIOSH): A 

Prevalence of hearing loss for noise-exposed metal/nonmetal miners. 

Franks, J.R., pp. 1-5. 

Pender, N, (1987) Health promotion in nursing practices (2nd Ed). 

Norwalk, CD: Appleton & Lange. 

Prochaska, J. O., DiClemente, C. C. (1992). Stages of change in the 

modification of problem behaviors. Progress in Behavioral Modification, 

28, 183-218. 

Randolph R.F., Kohler J.L., Byrne D. (2002). Communicating the 

same message with different media: An example from hearing loss 

prevention. Pittsburgh, PA: U.S. Department of Health and Human 

Services, Centers for Disease Control and Prevention, National Institute 

for Occupational Safety and Health, DHHS (NIOSH) Publication No. 

2002-154, IC 9463. 

Stephenson, M. R., Merry, C.J. (1998) Hearing loss among miners 

and measures to protect hearing. Holmes Safety Association Bulletin. 

October 1998. pp. 3-5. 

Suter, A.H., (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.