No. 531 September 2008 

Engineering Controls for Reducing

Continuous Mining Machine Noise
 

Objective 

To develop effective noise controls for continuous mining machines (CMMs) to reduce worker noise exposure. 

Background 

Noise-induced hearing loss (NIHL) is an occupational illness caused by chronic exposure to excessive 

sound levels. For underground coal mine workers, 

NIHL continues to be a serious health issue. Analysis 

of hearing loss data suggests that by retirement age, 

70%–90% of U.S. coal mine workers will have a hearing 

impairment. Operated in the confined spaces of 

underground mines, large industrial mining equipment 

often produces sound levels that can be harmful to 

workers. Of all equipment used in underground coal 

mining operations, CMMs account for the most noise 

overexposures. To reduce the occurrence of noise overexposures, engineering noise controls must be developed 

for the CMM. 

Approach 

Engineering noise controls address noise at the source to 

reduce sound levels and prevent NIHL. Noise generated by 

CMMs mainly results from three operational component systems: dust collection, cutting, and conveying. Of these three 

systems, the onboard conveyor system was found, through 

field and laboratory studies, to be the dominant noise source. 

Since sound levels produced by the conveyor system are 

higher than those of other component operations, noise controls targeting the conveyor system must be considered first 

for effective reduction of operator noise exposure. CMM 

conveyor noise is caused by impacts that occur between the 

conveyor deck and flight bars, which are used to move 

mined material to the discharge end of the machine. 

Research conducted by the National Institute for Occupational Safety and Health (NIOSH), with stakeholder involvement, has focused on producing noise treatments to reduce 

noise generated by the CMM conveyor system. 

Figure 1.—Urethane-coated flight bar chain. Figure 2.—Dual-sprocket driven chain. 
Two engineering noise controls have been developed 

to reduce CMM conveyor noise: the urethane-coated 

flight bar chain and the dual-sprocket chain. The urethane coating (Figure 1) used to treat the conveyor flight 

bars works by cushioning the impact blows of the bar on 

other parts of the conveyor. The dual-sprocket chain 

(Figure 2) reduces noise by maintaining a constant level 

of tension and by decreasing chain slack that otherwise 

produces high-intensity, noise-generating flight bar 

impacts at the conveyor transition points. 

Results 

Engineering noise controls for CMMs have been 

shown to reduce noise produced by the conveyor system. 

Laboratory sound power level measurements were conducted in the National Voluntary Laboratory Accreditation Program-accredited reverberation chamber at the 

NIOSH Pittsburgh Research Laboratory. These tests 

were performed to assess the acoustic performance of 

engineering noise controls in a controlled environment. 

A CMM with a urethane-coated flight bar chain installed 

reduced conveyor system noise by 7 dB(A), while a conveyor chain driven with the dual-sprocket system 

demonstrated a reduction of 3 dB(A). 

To fully evaluate these noise controls, underground 

testing needed to be performed. The urethane-coated 

flight bar chain and dual-sprocket flight bar chain were 

installed on different machines at different underground 

coal mines. The urethane-coated flight bar chain demonstrated an 8-hour time-weighted average exposure 

reduction of 3 dB(A). The urethane coating also 

extended chain life by preventing any chain link failures 

during the 6-month test period. (A failure rate of three 

failed links in 4 months is typical for standard chains in 

similar mine conditions). The dual-sprocket chain 

showed promise for reducing operator exposure close to 

the Mine Safety and Health Administration (MSHA) 

permissible exposure level (PEL) and for achieving compliance with Title 30 of the Code of Federal Regulations 

(CFR). 

Recommendations 

Targeting noise at the source through engineering noise 

controls reduces operator overexposure to noise. Title 30 of 

the CFR requires any mining machine operator who is above 

the PEL to use all feasible engineering and administrative 

noise controls. Both the urethane-coated flight bar chain and 

the dual-sprocket chain are considered by MSHA to be 

“technologically and administratively achievable.” These 

engineering controls should be considered mandatory when 

CMM operators are overexposed to noise. 

For More Information 

Publications on hearing loss prevention in the mining industry can be downloaded from the NIOSH Mining Web site at: 

http://www.cdc.gov/niosh/mining/pubs/programareapubs14.htm 

For more information about the urethane-coated flight 

bar chain or the dual-sprocket chain for reducing noise 

exposure, contact Adam K. Smith, NIOSH Pittsburgh 

Research Laboratory, P.O. Box 18070, Pittsburgh PA 15236-

0070; phone: (412) 386-6028; e-mail: ASmith9@cdc.gov. 

To receive NIOSH documents or for more information 

about occupational safety and health topics, contact: 

1–800–CDC–INFO (1–800–232–4636), 1–888–232–6348 

(TTY), e-mail: cdcinfo@cdc.gov, or visit the NIOSH 

Web site at http://www.cdc.gov/niosh 

Mention of any company name or product does not constitute endorsement by the National Institute for Occupational Safety and Health. 

DHHS (NIOSH) Publication No. 2008–145