NOISE EXPOSURE IN LONGWALL MINING AND 

ENGINEERING CONTROLS RESEARCH
 

E. R. Bauer, D. J. Podobinski, E. R. Reeves 

National Institute for Occupational Safety and Health 

Office of Mine Safety and Health Research 

Pittsburgh Research Laboratory 

Pittsburgh, PA
 

J. S. Vipperman 

Department of Mechanical Engineering 

University of Pittsburgh 

Pittsburgh, PA 

ABSTRACT 

Prolonged exposure to noise can cause permanent damage to the auditory nerve and/or its sensory components, known as 

noise induced hearing loss (NIHL). It is the most common occupational disease in the United States today. The 

Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) is 

addressing NIHL in the mining industry through several research efforts. This paper presents a general review of NIHL, 

the status of NIHL in mining, the results of the longwall noise surveys, and a review of the longwall engineering controls 

research efforts. 

INTRODUCTION 

Noise is often regarded as a nuisance rather than as an occupational hazard. However, overexposure to noise can cause 

serious hearing loss. In 1996, NIOSH reported that occupational hearing loss was the most common occupational 

disease in the United States, with 30 million workers exposed to excessive noise levels [NIOSH, 1996]. The problem is 

particularly severe in the mining industry, with studies indicating that 70% to 90% of miners have a NIHL great enough 

to be classified as a hearing disability [NIOSH, 1976; Franks, 1996]. This alarming prevalence of severe hearing loss 

among miners is demonstrated in Figure 1. The general trend among the three groups is an increase in hearing loss with 

increasing age. As an example, by age 50, 70% of coal miners and nearly 60% of non-coal miners have a hearing loss of 

more than 25 dB, compared to only 10% for non-exposed males. 

Since the passage of the Federal Coal Mine Health and Safety Act of 1969, there has been some progress in controlling 

mining noise. Machinery manufacturers have incorporated design changes to reduce noise levels. At the same time, 

many of these gains have been offset by the use of larger, more powerful, equipment. Thus, the number of miners 

overexposed to noise, as defined by federal regulations, still exceeds the number of miners overexposed to all other 

health hazards. Data from over 60,000 Mine Safety and Health Administration (MSHA) noise surveys show 

that the noise exposure of selected occupations has decreased since the 1970s, although the percentage of miners 

overexposed in relation to current MSHA noise regulations remains high [Seiler et al., 1994]. MSHA found that the 

percentage of coal miners with noise exposures exceeding federal regulations, unadjusted for the use of hearing 

protection, were 26.5% and 21.6% for surface and underground mining, respectively. Table 1 lists recently published 

data from MSHA noise surveys of exposures in the mining industry [Federal Register, 1999] and indicates that more 

than 25% of the samples collected in coal mines exceeded the Permissible Exposure Level (PEL) (an eight hour Time 

Weighted Average ( TWA8) of 90 dBA) and nearly 77% exceeded the action level (a TWA8 of 85 dBA) for enrollment 

in a hearing conservation program. On a percentage basis, a smaller percent of samples, taken in metal/nonmetal mines, 

exceeded the PEL and action level. These data are corroborated by data collected in the National Occupational Health 

Survey of Mining (NOHSM) during the 1980s [Greskevitch et al., 1996]. Based on this survey, the projected number of 

mine workers potentially overexposed to noise was approximately 200,000 workers, or 73% of the workforce. 
Industry 

segment 

TWA8 sound level, 

dBA 

90-dBA t

Number of 

samples 

hreshold 

Percent of 

samples 

80-dBA t

Number of 

samples 

hreshold 

Percent of 

samples 

Coal1 90 (PEL) 1075 25.3 ------------ ------------ 

85 (Action Level) -------------- -------------- 3268 76.9 

Metal/ 

Nonmetal2 

90 (PEL) 7360 17.4 ------------ ------------ 

85 (Action Level) -------------- -------------- 28,250 66.9 

 1

Collected from March 1991 through December 1995. 

 2

Collected from March 1991 through December 1994. 

Figure 1 

Hearing impairment in coal miners, non-coal miners, and non-exposed males (from Franks, 1996)
 

Table 1 

MSHA noise samples exceeding specified TWA8 sound levels
 

In response to the continuing problem of NIHL among mine workers, NIOSH has begun a number of research efforts 

designed to reduce NIHL among mine workers. These efforts include education and training, effective use of personal 

protective equipment, noise source and worker dose monitoring, and engineering controls research. 

FUNDAMENTALS OF NOISE INDUCED HEARING LOSS 

Noise is any unwanted or undesirable sound. NIHL has been around for centuries, and first received attention with the 

advent of steam power during the industrial revolution. In fact, it was initially dubbed Aboilermaker=s disease@ because of 

the hearing loss experienced by workers fabricating steam boilers [U.S. Dept. of Health and Human Services, 1998]. 

NIHL can be temporary or permanent depending on the level and frequency characteristics of the noise, the duration of 

exposure, and the susceptibility of the individual. Temporary hearing loss can last a matter of hours to several days or 

weeks. A permanent noise-induced hearing loss is not reversible and cannot be corrected by conventional medical or 

surgical procedures [Michael and Byrne, 2000]. Permanent NIHL is caused by exposure to sound levels or durations that 

damage the hair cells of the cochlea located in the inner ear (Figure 2). Hearing acuity is generally affected first in the 
 

 

 

 

 

 

frequency range from 3000 to 6000 Hertz (Hz). People with NIHL do not generally experience pain or even realize that 

serious hearing damage has occurred. They may hear a continuous ringing in their ears, called tinnitus. A noise-induced 

hearing loss becomes particularly noticeable when verbal communication is attempted in noisy or reverberant areas. 

Figure 2 

Diagram of human ear (Cochlea is listed as Hearing Canal)
 

HISTORY OF NOISE REGULATIONS IN MINING 

Regulation of noise in mining is covered in Title 30 of the Code of Federal Regulations (30 CFR). The Federal Coal 

Mine Health and Safety Act of 1969 established requirements for protecting coal miners from excessive noise and, 

subsequently, the Federal Mine Safety and Health Act of 1977 broadened the scope to include all miners, regardless of 

mineral type [30 CFR, 1977]. The regulations allowed a PEL of 90 dBA TWA over eight hours. Exposure below the 

criterion of 90 dBA was unregulated, while continuous exposure to levels greater than 115 dBA was not permitted. 

Despite the extensive work done to reduce noise overexposure in the 1970s and 1980s, NIHL in mine workers is still a 

problem. Therefore, MSHA has published new Noise Health Standards for Mining [Federal Register, 1999]. The new 

rule-making efforts were adopted in September 1999 and became effective in September 2000. They include a PEL of 

90 dBA TWA8, and a new action level for workers exposed to a dosage over 50% of the PEL (which is 85 dBA TWA8). 

Moreover, the new rule establishes the primacy of engineering and administrative noise controls, and eliminates credit 

for the use of personal hearing protection. Additional criteria include a dual hearing protection level of 105 dBA TWA8 

and a stipulation that no miner is exposed to sound levels exceeding 115 dBA. Specific details of the new regulations are 

listed in Table 2. 

 

 

Type 

TWA8, 

dBA Dose 

Sound Levels 

Integrated, dBA 

Exchange 

rate, dB Weighting Response 

Action level 85 50% 80 to 130 5 A Slow 

Permissible 

exposure level 90 100% 90 to 140 5 A Slow 

Table 2 

Details of Part 62 of 30 CFR - Occupational noise exposure measurements 
 

 

 

CROSS-SECTIONAL SURVEY OF NOISE EXPOSURE 

NIOSH is obtaining multishift worker noise exposure and equipment noise levels to develop a comprehensive profile of 

the noise exposures to the mining population as a function of equipment- and activity-specific measures. This study is a 

component of the effort to develop noise controls. It will define the sources of miners= exposures and the characteristics 

of those sources. This information will enhance ongoing efforts focusing on the development and application of 

appropriate engineering and administrative control measures to reduce exposures for mine workers. Data collection is 

being performed at underground and surface coal and metal/nonmetal mines and in coal processing plants. It is 

necessary to survey all segments of the mining industry because workers across the industry continue to have a 

significant risk of hearing impairment, as described by MSHA data published in the Federal Register [1999]. 

At each mine site, the data collected include worker noise dose, equipment noise, and other worker, mine, and 

equipment-specific information; utilizing the same procedure at all mines. Mine workers wear Quest Model Q 400 timeresolved dosimeters with the microphones pinned on the top, middle of the shoulder. Workers are observed to determine 

the correlation between tasks performed, noise dose received, and the noise source responsible for that incremental 

contribution to the overall exposure. Noise profiling of longwall and continuous miner section equipment, consisting of 

A-Weighted Equivalent Continuous Sound Levels (Leq) measurements on a uniform grid pattern (usually 3.28 ft (1 m) 

square), is conducted using Quest Model 2900 Integrating and Logging Sound Level Meters (Figure 3). In general, Leq 

noise levels were recorded using tripod-mounted SLMs, with microphones at 5-5.5 ft (1.5-1.7 m) from the mine floor 

(approximate ear height). Where possible, measurements were made completely around the equipment and at a distance 

away until the Leq level dropped below 90 dBA. Table 3 lists the dosimeter and SLM settings. 

Figure 3 

Dosimeter and Sound Level Meter used in study 

Longwall Noise Surveys 

Noise surveys were conducted on three longwall faces. The first survey was completed at a mine in southern West 

Virginia operating in the Lower Cedar Grove coalbed. A second study was conducted in Colorado, in a mine operating 

in the Wadge coalbed. The final study was completed in a longwall mine in northern West Virginia operating in the 

Pittsburgh coalbed. In addition, in each of the mines, noise surveys were completed on the continuous miner (CM) 

sections during gate road development. A summary of equipment noise profiling (Leq) and worker dose monitoring at 

each site follows. 
Parameters 

Type Instrument 

MSHA PEL Wide Range 

Weighting - A 

Threshold Level - 90 Weighting - A 

Worker 

Dose 

Quest Q-400 

Dosimeter 

dB 

Exchange Rate - 5 dB 

Criterion Level - 90 dB 

Threshold Level - 40 dB 

Exchange Rate - 3 dB 

Criterion Level - 85 dB 

Response - Slow Response - Slow 

Upper Limit - 140 dB Upper Limit - 140 dB 

Parameters 

Equip. 

Profiling 

Quest 2900 

Sound Level 

Meter 

Weighting - A 

Exchange Rate - 3 dB 

Response - Slow 

Range - Variable (60 - 140 dB) 

Memory - On 

Measurement - Leq, dBA 

 

 

 

Table 3 

Noise monitoring parameters
 

Southern West Virginia Mine 

The longwall at this mine was operating in the Lower Cedar Grove coalbed, which was 55-70 in (1.4-1.8 m) thick. 

Mining height averaged 72-84 in (183-213 cm), including 12-20 in (30.5-51 cm) of rock, for reject averaging 40%. 

Equipment noise profiling (Table 4) and full shift (10hr) worker noise dosimetry was conducted (Table 5). At this mine, 

only the headgate operator and headgate shearer operator were task-observed; an example plot is shown in Figure 4 and 

illustrates some of the tasks responsible for the headgate operator=s dose. 

Equipment Range of noise 

(Leq), in dBA 

Location of Highest Leq Noise 

Level 

Stageloader 84 – 98 head drive, crusher, gear boxes 

Hydraulic pump car 85 – 98 motors and hyd. pumps 

Shearer (Headgate) 

Shearer (Tailgate)

 

 

 96 

98 

ND1 

ND 

Panline 81 – 87 near head drive 

Dinner hole <60 None 

1

ND - Not determined 

Table 4 

Results of equipment profiling on longwall in southern West Virginia mine 
R

Location Workers Monitored No. of 

S

Head Shearer Operator 

Tail Shearer Operator 

Headgate Operator LW1 

Jacksetter 

Electrician 

Foreman 

CM Operator 

CM Helper 

Roof Bolter, Right 

Roof Bolter, Left 

CM2 Shuttle Car Operator 

Scoop Operator 

esults of Do

R

hifts 

3 

3 

3 

6 

3 

3 

3 

3 

3 

2 

6 

3 

se Monitoring 

Tons ange of PEL 

Dose, % 

185-266 

290-786 

142-179 6600-

81-188 8140 

76-126 

61-203 

222-323 

201-347 

142-247 

133-234 990- 70-165 1135 24-44 

Brattice Man 

Electrician 

Foreman 

1

LW – Longwall; 2CM – Continuous Mining 

2 

3 

3 

37-53 

36-92 

39-114 

 

 

Table 5 

Summary of dosimeter measurements in southern West Virginia mine 

100% Dose 

Figure 4 

Cumulative dose plot for headgate operator from southern West Virginia mine 

Colorado Mine 

This mine was operating in the Wadge coalbed, which averaged 8.25 to 9.5 ft (2.5 to 2.9 m) thick. In most instances 

there was very little inseam rock. Leq noise level values were recorded for the longwall equipment (Figure 5) and all 

longwall workers wore a noise dosimeter for three full (10 hr) shifts. Table 6 summarizes the equipment noise levels and 

Table 7 summarizes the results of the dosimeter measurements. 
 

 

Figure 5 

Noise levels measured along the stageloader and panel belt in Colorado mine 

Range Equipment (Leq),

Stageloader 89 – 102 

Longwall hydraulics 82 – 

Shearer 85 – 

Panline 85 – 

Head drive 89 – 

Tail drive 92 – 

Dinner hole 63 – 

of noise Location of Highest Leq Noise 

 in dBA Level 

bridge conveyor 

98 motors and hyd. pumps 

ND1 90 

91 near head drive 

96 ND 

94 ND 

68 None 

1

ND - Not determined
 

Table 6 

Results of equipment profiling on longwall in Colorado mine
 

Northern West Virginia Mine 

This mine was operating in the Pittsburgh coalbed. Mining height averaged 82-86 in (208-218 cm), composed of 5 to 6 

ft (1.5 to 1.8 m) of coal, overlain by 2 to 24 in (5 to 61 cm) of draw rock, followed by 1 to 24 in (2.54 to 61 cm) of top 

coal. In most instances, this resulted in a rock content of approximately 30%. Equipment noise profiling (Figure 6) and 

worker dose monitoring (9 hr, full shift) were conducted. Table 8 presents the results of the equipment noise profiling 

and Table 9 summarizes the results of the dosimeter measurements. Task observations were conducted on the headgate 

(Figure 7) and tailgate shearer operators only. 
Results of Dose Monitoring 

Location Workers Monitored Tons No. of Range of PEL 

Shifts Dose, % 

Shearer Operators1 6 164-355 

Headgate Operator 3 233-386 14318- LW Faceman 9 64-192 22610 

Mechanic 6 64-156 

CM Operator 4 48-197 

CM Helper 4 44-132 

Roof Bolter, Right 4 77-213 

Roof Bolter, Left 4 57-230 

Roof Bolter Helper 3 222-355 1070- CM Shuttle Car Operator 7 23-109 1692 

Scoop Operator 4 150-210 

Utility Man 2 19-168 

Mechanic 3 34-162 

Foreman 4 131-232 

1

Shearer operators switched from head to tail position when shearer direction changed. 

Comparative Analysis of Mine Sites 

Table 7 

Summary of dosimeter measurements in Colorado mine
 

Figure 6 

Leq noise levels around shearer while cutting from head to tail in northern West Virginia mine 

A comparison of the noise surveys at the three mines indicates the following: 

$ Noise levels of similar equipment found in each mine was relatively consistent, although the range of Leq 

noise levels varied. 

$ Worker exposures were also similar from one mine to the other. 

$ Worker dose varied widely from shift-to-shift indicating that single shift dose measurement is not sufficient 

for determining compliance. 

$ Little correlation was found between production and equipment noise levels and worker dose. 
Equipment Range of noise 

(Leq), in dBA Location of Highest Leq Noise Level 

crusher, motor, and gear box at tail 

Stageloader 86 – 100 piece 

Hydraulic pump car 78 – 99 motors and hyd. Pumps 

Shearer (head to tail) 88 - 99 adjacent to tail drum 

Shearer (tail to head) 86 – 96 adjacent to head drum 

Panline (full) 78 – 80 near head drive 

Section belt 83 – 96 roller with worn out bearings 

Dinner hole <70 – 90 when located next to stageloader 

Location Workers Monitored 

Results of Dose Monitoring 

Tons No. of 

Shifts 

Range of PEL 

Dose, % 

LW 

Head Shear Operator 

Tail Shear Operator 

Shieldman 

Mechanic 

Foreman 

3 

3 

10 

4 

3 

125-179 

124-240 

49-138 

37-99 

102-123 

3145-

5550 

CM 

CM Operator 

LM Operator 

Roof Bolter, Right 

Roof Bolter, Left 

Roof Bolter, Center 

Shuttle Car Operator 

Utility Man 

Mechanic 

Foreman 

3 

3 

3 

3 

3 

6 

1 

3 

2 

88-127 

58-81 

169-275 

128-185 

18-33 

9-34 

297 

8-68 

17-36 

186-

325 

 

Table 8 

Results of equipment profiling on longwall in northern West Virginia mine
 

Table 9 

Summary of dosimeter measurements in northern West Virginia mine.
 

NOISE SOURCE LOCATION USING SOUND INTENSITY TECHNIQUES 

Prior to expending time or money on solving a noise problem, the number, strength, and location of the major noise 

source(s) should be determined. Only after source identification and quantification, can cost-effective engineering 

and/or administrative noise control solutions be implemented. The preferred way to reduce worker noise exposure is to 

contain or control the noise at its source. This is referred to as engineering noise control. When properly installed and 
maintained, this type of control requires no further action on the part of the worker to reduce his/her noise exposure. For 

this reason, the primacy of engineering controls was emphasized in the enactment of Part 62 of 30 CFR [Federal 

Register, 1999]. 

Figure 7 

Cumulative dose plot for head shearer operator in northern West Virginia mine 

When implemented properly, engineering controls can be a cost effective proposition. A systematic approach to noise 

control can ensure control efforts are targeted to necessary areas. Systematic approaches to resolving noise control 

problems are outlined in many texts. A suggested sample approach is: 

(i)	 Define the problem - Operation of various mining equipment often causes the worker exposure to 

exceed the PEL. 

(ii)	 Establish the goal and scope of the program. - For example, the goal may be to reduce worker 

exposure to below the action level requiring enrollment into a hearing conservation program. 

(iii)	 Qualitatively identify source(s), path(s) and receiver(s) - These are the steps currently being 

addressed by many in the mining industry. 

(iv)	 Draw an acoustical free body diagram that identifies all noise sources, air-borne and structureborne paths to the receiver. 

(v)	 Quantitatively rank the sources and paths with analysis tools. 

(vi)	 Determine the merits of source-path-receiver controls. 

(vii)	 Identify direct and reverberant field contributions. 

(viii)	 Isolate flanking paths and their significance. 

(ix)	 Identify and rank structure-borne and air-borne paths. 

(x)	 Give careful consideration to all possible controls. 

(xi)	 Select combination of controls that is most effective for the budget. 

(xii)	 Apply controls and evaluate results, then compare with expected results. 

Why Sound Intensity? 

Sound intensity measurement is a technique for identifying and ranking noise sources (Steps 3 and 5 above). Sound 

level meters (SLMs) and dosimeters, currently in widespread use within the industry, use one microphone to measure 

sound pressure. Sound pressure, being a scalar quantity and having magnitude only, does not provide the source 

location. Sound intensity analyzers utilize two microphones in close proximity to one another (Figure A1). The 

additional microphone provides directional information, making sound intensity a vector, having both magnitude and 

direction. This directional aspect of the sound intensity measurement enables one to say, for example, AThe noise 
 

 

 

 

 

 

 

 

 

generated by this machine originates in the lower right hand corner @ as opposed to simply saying AThis machine is 

noisy.@ This additional information allows manufacturers, equipment rebuilders and maintenance personnel to focus on 

and treat the actual noise source rather than try to enclose the entire machine in an attempt to reduce its overall noise 

level. 

Longwall Engineering Controls Research 

Background 

Dosimetry information has identified the area adjacent to the longwall stageloader as one of the higher noise areas in the 

underground mining environment. The size, complexity and mobility of the stageloader, and the height of the coal seam, 

preclude the use of operator enclosures or most other means to isolate the equipment noise from the workers in the 

immediate area. Sound intensity measurement techniques were used to locate and identify the specific source(s) of noise 

within the stageloader assembly. Pinpointing the noise source would minimize the engineering control effort. 

Many equipment manufacturers assemble and test run the equipment prior to shipment to the mine because it is difficult 

to modify large underground mining equipment once installed and operational. This allows for easier identification of 

potential problems and for making the necessary modifications before it is installed in an operating underground mine. 

The manufacturer and end user of this particular stageloader allowed us to conduct a sound intensity survey of the unit 

while it was being operated in the manufacturer=s shop. Results of the survey were shared openly among all parties 

involved. 

Measurement Technique 

The stageloader assembly was divided into areas that were consistent with the manufacturer=s nomenclature. This 

particular stageloader was divided into the discharge zone - the horizontal section located directly over the belt tailpiece; 

and the gooseneck zone - the area between the crusher and the discharge zone. Initially, because of uncertainty that 

sound intensity measurements could effectively locate the source(s) of the equipment noise, no measurements were made 

in the area between the crusher and the headgate drive. 

Each zone to be measured was then placed in an imaginary Abox.@ The purpose of the box was to provide planar 

measurement surfaces that completely enclose the device under test and allow for evaluating all sound coming from 

within a particular volume. All sides of the box are referred to as surfaces. Each surface is then broken down into 

segments. For these measurements, each segment was 18 in by 18 in (0.45 m by 0.45 m). These dimensions were 

chosen by considering the frequency range of interest, the overall size of the stageloader, and the guidelines for 

determining the minimum number of measurement points required to produce valid results using the fixed-point 

measurement technique [ANSI, 1992]. 

Measurements are then made normal (at 900

) to the surface and averaged over fifteen seconds at the center of each 

segment using a B&K 2260 Noise Investigator. To insure a consistent spacing between the probe and the measurement 

surface, a 3.9 in (10 cm) long plastic spacer was attached to the microphone probe. The selected spacer rod did not allow 

vibrations to be transferred to the microphone probe, and was diametrically small enough to not affect the measurement. 

Sound Intensity Measurement Results 

The results of the sound intensity measurements taken on the side of the stageloader gooseneck zone are shown in Figure 

8. Measurements were made at each of the grid intersections. The information was processed by the B&K 2260 Noise 

Investigator, and plotted using Microsoft Excel. Figure 8a illustrates an apparent source of high intensity located in the 

lower right hand corner of the gooseneck assembly. It can also be seen that the intensity lessens as the distance from the 

alleged source increases, indicating that it was not an errant data point causing the high reading. 

This area corresponds to the lower deck of the gooseneck immediately adjacent to the crusher assembly. Upon 

disassembly prior to shipment to the mine site, the manufacturer found an area of interference in this lower deck region 

that resulted in the flight bars contacting the conveyor deckplate. This problem was addressed prior to shipment. 

Because the measurement technique appeared to effectively locate noise sources, we were asked to repeat the 

measurements after implementation of engineering controls. The controls selected by the manufacturer were 
implemented in two phases: first, additional panels were installed onto the side of the stageloader in areas that were easy 

to access; and next, the void created by the addition of these panels was filled with sand. Both of these control ideas 

attempted to dampen the noise generated by the operation of the stageloader by increasing the mass of the structure. The 

results of these measurements are shown in Figures 8b and 8c respectively. 

Figure 8 

Sound intensity measurements of gooseneck assembly 

Sound Power Measurements 

The addition of sand resulted in a decrease in localized sound intensity, as shown in Figure 8c. However, an increased 

area of higher sound intensity occurred, making it difficult to tell if the treatment was effective in reducing the overall 

noise level of the equipment. Sound power (watts), which is the total sound energy radiated by the source per unit of 

time, can be used to evaluate noise level reductions. 

Several recognized national standards are available to compute sound power from sound intensity measurements. The 

method specified in ISO 9614-1 is shown here for illustrative purposes. The sound power level of the device under test 

is: 

⎛∑IniSi ⎞

Lw = 10× log⎜ ⎟ dB, ⎜ ⎟ Po ⎝ ⎠

where: Ini = the sound intensity measured at the ith segment, in watts/square meter; 

Si = the area of the ith segment, in square meters; and 

P0 = the sound power reference or 1 picowatt (10-12 watts). 

Sound power measurements are typically used to quantify the total energy being emitted by a noise source. In this 

example, we used the sound power emitted by one surface to compare the before-and-after results of the application 

of an engineering control. The relationship of sound power emitted by the noise source and the sound pressure that 

impinges on the ear of the worker is analogous to the situation shown in Figure 9. For a constant electrical input to 

the heater, the power given off by the heater (analogous to sound power) is constant. The temperature perceived by 

the individual (analogous to sound pressure) depends on both the environment (size of room, number of windows 

and doors, and whether they are opened or closed), and the distance from the heat source. In general, if you can 

lower the amount of power generated by the source, the temperature (or sound pressure) perceived by the individual 
will be less, if the distance and environment are constant. The effectiveness of engineering controls can be 

evaluated and compared by determining the sound power emitted by the source. 

Figure 9 

Analogy of sound power and thermal power [Rasmussen, 1998] 

The sound power levels for these three areas are shown in Table 10. 

Reference 

Figure 

Condition Sound Power 

Level, dB 

8a 

8b 

8c 

Unmodified (base case) 

Partially paneled 

Filled with sand 

111.9 

114.0 

111.7 

Table 10 

Sound power levels for stageloader gooseneck areas – one side surface only
 

Future Longwall Engineering Control Efforts 

The following sound intensity surveying activities are planned: 

$ Measure the power unit (motor, fluid coupler, gear case) to quantify the noise generated by water-cooled 

motors. 

$ Measure the effect of flight bar spacing on overall stageloader noise levels. 

$ Perform follow-up measurements on this particular stageloader to quantify the effects of aging and coal 

loading on the generated noise levels. 

$ Use accelerometers to measure panel vibration and modal effects both before and after a modification is 

made. 
 

 

DISCUSSION 

The result of exposure to high noise levels can be a permanent hearing loss termed Noise Induced Hearing Loss 

(NIHL). Studies have shown that over 70% of mine workers are at risk of overexposure to noise, and that 60 to 70% 

of all mine workers will have a 25 dB or greater hearing loss by age 50. 

The results of the preliminary worker dose monitoring revealed that approximately 47% of the longwall workers 

monitored experienced noise dosages above the allowable (citable) PEL of 132% (90 + 2 dB). The workers most 

consistently experiencing doses above 132% include the shearer operators and headgate/stageloader operators. 

Other workers who occasionally are exposed to noise doses above 132% include the shieldmen/jacksetters, 

mechanics/electricians, and foremen. On the CM sections, face crew worker noise doses were above 132% only 

39% of the time. The workers consistently above this level included the roof bolter operators, foremen, and at one 

mine, the CM operator and helper. In addition, significant variation exists in the full-shift doses. 

The noise profiling of the longwall equipment revealed that the stageloader was generally the noisiest piece of 

equipment, followed by the shearer and hydraulic pump car/assembly. This equipment consistently generated noise 

levels greater than 90 dBA. It was found that the face conveyor (panline) and section belt developed noise levels ranging 

from 80 to 90 dBA. Many more pieces of equipment on the CM section generated noise levels above 90 dBA, including 

the roof bolter, continuous miner, feeder/breaker, auxiliary fans, scoop, miner/bolter, and loading machine. Nearly all 

other equipment emitted noise levels greater than 80 dBA during operation. 

Finally, it was demonstrated that sound intensity can be used to locate noise sources on a longwall stageloader and 

possibly other mining equipment. Using this technique can reveal unexpected noise sources that can then be 

corrected prior to field installation. It was also demonstrated that filling side panels with sand may decrease sound 

levels. Further testing is needed to verify if this can reduce noise levels if applied to the entire stageloader assembly. 

In addition, the motor cooling fan contributes to the overall noise level of the stageloader power unit. 

REFERENCES 

ANSI, 1992, Engineering Method for the Determination of Sound Power Levels of Noise Sources Using Sound 

Intensity, S12.12, American National Standards Institute, New York, 19 pp. 

CFR 30, 1997, Code of Federal Regulations (CFR) governing noise exposure in mining, CFR 30, Subchapter O, 

Part 70, Subpart F: Noise Standards for Underground Coal Mines; Subchapter O, Part 71, Subpart D: Noise 

Standards for Surface Work Areas of Underground Coal Mines and Surface Coal Mines; Subchapter O, Part 55, 

Section 55.5: Metal and Nonmetal Open Pit Mines; Section 56.5: Sand, Gravel, and Crushed Stone Operations 

and 57.5: Metal and Nonmetal Underground Mines. 

Federal Register, 1999, Health Standards for Occupational Noise Exposure; Final Rule, Department of Labor, Mine 

Safety and Health Administration, 30 CFR Parts 56, 57, 62, 70 and 71, 64 (176), September 13, pp. 49548-

49634. 

Franks, J.R., 1996, Analysis of audiograms for a large cohort of noise-exposed miners, Internal Report, National 

Institute for Occupational Safety and Health, Cincinnati, OH, pp. 3-8. 

Greskevitch, M.K., T.S. Bajpayee, D.W. Grace, J.M. Hale, and F.J. Hearl, 1996, AResults from the National 

Occupational Health Survey of Mining (NOHSM),@ DHHS (NIOSH) Publication No. 96-136, September, pp. 17-

18. 

ISO 9614-1, 1993, Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 1: 

Measurement at discrete points, International Organization for Standardization, Geneva, Switzerland, 24 pp. 

Michael, K.L. and D.C. Byrne, 2000, Industrial Noise and Conservation of Hearing, Chapter Nineteen in Patty=s 

Industrial Hygiene, Fifth Edition, Volume 2, Edited by R.L. Harris, John Wiley & Sons, Inc., pp. 15-16. 

NIOSH, 1996, National Occupational Research Agenda (NORA), National Institute for Occupational Safety and Health, 

Publication No. 96-115, p. 14. 

NIOSH, 1976, Survey of Hearing Loss in the Coal Mining Industry, National Institute for Occupational Safety and 

Health, Publication No. 76-172, June, 70 p. 

Rasmussen, G., 1989, Intensity - Its Measurement and Uses, Sound and Vibration, 23 (3), March, pp. 12-21. 
Seiler, J.P., M.P. Valoski, and M.A. Crivaro, 1994, Noise Exposure in U.S. Coal Mines, U.S. Dept. of Labor, Mine 

Safety and Health Administration, Informational Report IR 1214. 

U.S. Department of Health and Human Services, 1998, Criteria for a Recommended Standard, Occupational Noise 

Exposure, Revised Criteria 1998, U.S. Dept. of H&HS, Public Health Service, Centers for Disease Control and 

Prevention, NIOSH, Cincinnati, OH, June, p. 11. 

APPENDIX – Sound Intensity Theory 

Sound intensity at any point in a sound field is defined as the average rate of flow of sound energy transmitted in a 

specified direction through a unit area normal to this direction at the point considered. Sound intensity is measured in 

units of watts per square meter. The letter AI@ is used when referring to intensity. The mathematical formula for sound 

intensity is the dot product of the sound pressure and the particle velocity (p . v) (Refer to Figure A1). The sound 

pressure used in the calculation is the average of the two pressures measured by the two microphones (Pa, Pb). The 

particle velocity is determined by using the finite difference approximation developed by Euler. 

1 ∂p Velocity(v) = ∫ ρ 

dt, ∂r
 

where ρ is the density of air, 

p is pressure, and 

r is the separation distance between the microphones. 

This partial derivative can be approximated by 

1 (Pb − Pa)

v = − dt, ∫ ρ Δr 

where Pa and Pb are readily measured. 

Figure A1 

Microphone spacing for sound intensity measurements [Rasmussen, 1989]