MINING ENGINEERING

Revised manuscript accepted for publication December 2007. 

Discussion of this peer-reviewed and approved paper is invited and 

must be submitted to SME Publications Dept. prior to June 30, 2008.

Snapshot of noise and worker exposures 


in sand and gravel operations
 

E.R. BAUER AND E.R. SPENCER 

E. R. Bauer, member SME, and E.R. Spencer are lead research 

engineer and research engineer, respectively, with the Hearing 

Loss Prevention Branch, Pittsburgh Research Laboratory, National 

Institute for Occupational Safety and Health, Pittsburgh, PA.Paper 

number TP-07-034. Original manuscript submitted October 2007. 

Abstract

Previous studies and research efforts have shown that 

noise-induced hearing loss (NIHL) is a problem in the U.S. 

mining industry. In response, researchers at the National 

Institute for Occupational Safety and Health (NIOSH) 

have been conducting a cross-sectional survey of equipment noise and worker noise exposures in the mining 

industry to estimate the potential for NIHL within the 

mining community. One commodity recently surveyed 

was the extraction of sand and gravel from surface pits 

and by dredging.To address the potential for NIHL in the 

sand and gravel industry, sound levels on and around the 

dredges and processing equipment were recorded to identify areas of high noise levels. Full-shift worker dosimetry, 

in conjunction with task observations, was documented to 

determine the relationship between exposure and source. 

This paper presents research examining noise on dredges 

used in several surface mine sand and gravel operations 

and in the processing facilities. Results indicate that there 

are areas on the dredges (crane, suction pumps and diesel 

engines) where sound levels greater than 90 dB(A) are present. In addition, crushers and screens used in the processing 

of the sand and gravel also generate sound levels greater 

than 90 dB(A). Although no surveyed worker exceeded 

the Mine Safety and Health Administration’s (MSHA’s) 

permissible exposure level (PEL) of 90 dB(A) eight-hour 

time-weighted average (TWA8), laborers, mechanics, oilers, 

helpers, pickers and greasers are the workers most likely to 

be exposed to hazardous sound levels and to thus develop 

NIHL over time. 

Introduction	 Exposure to noise and noiseinduced hearing loss (NIHL) continues to be problematic for the 

U.S. mining industry. The problem	 

is particularly severe because large, 

noisy equipment is found throughout the industry.A National Institute 

for Occupational Safety and Health 

(NIOSH) analysis of NIHL among 

miners illustrates the extent of NIHL 

audiograms indicates the number of miners with hearing impairments (defined as an average hearing threshold level of 25 dB or greater for the frequencies 1,000, 

2,000, 3,000 and 4,000 Hz) increased with age until age 

50, at which time 49 percent of the metal/nonmetal and 

90 percent of the coal miners had a hearing impairment 

(NIOSH, 1996, 1997). 

Another NIOSH study looked specifically at noise 

exposure and hearing loss among

sand and gravel miners (Landen et 

al., 2004). These studies were conducted at 24 surface and nine dredge

operations.The results revealed that 

69 percent of the miners’ noise exposures exceeded the NIOSH recommended exposure limit (REL) of 

(85 dB,A-weighted, as an eight-hour 

time-weighted average (TWA8)). 

In addition, 41 percent exceeded 

MSHA’s action level for enrollment in the mining industry. This analysis of several thousand in a hearing conservation program. Landen also reported 

that hearing protection use was low, with 48 percent of 

the subjects reporting that they never used hearing protection. To address NIHL issues in all mining, MSHA 

has published Health Standards for Occupational Noise 

Exposure (Federal Register, 1999). Requirements of the 

new standard include: 

• 	 the adoption of an Occupational Safety and Health 

Administration (OSHA)-like Hearing Conservation Program (HCP), 

• 	 enrollment in the HCP for workers exposed above 

an action level of 85 dB(A) eight-hour time weighted average (TWA8), 

• 	 reduction of worker exposures to or below a permissible exposure level (PEL) of 90 dB(A) TWA8 

or equivalently a dose of 100 percent, 

• 	 no reduction in noise exposure being allowed due 

to the use of personal hearing protection and 

• 	 a requirement that mine operators use all feasible 

engineering and administrative controls to reduce 

noise exposures. 

NIOSH responded to the problem of noise overexposure in the mining industry by conducting an extensive 

cross-sectional survey of noise sources and worker noise 

exposures. Initially, these surveys were conducted in surface and underground (room and pillar and longwall) 

coal mines, coal preparation plants, stone (aggregate) 

mines and crushing and processing facilities. Recently, 

these surveys have expanded to sand and gravel mines, 

including dredging and their associated crushing, sizing 

and processing facilities. According to MSHA, in 2005 

there were more than 7,000 sand and gravel operations 

(approximately 6,200 surface and 800 dredges) in the 

United States disbursed as shown in Fig. 1. Employment 

in the sand and gravel industry exceeded 45,000 workers, 

with an average of six employees per mine. These surveys are designed to monitor worker noise dose, measure 

equipment sound levels and understand the noise source/ 
MINING ENGINEERING MARCH 2008 51

worker dose relationship. This is accomplished through 

full-shift dosimetry readings, equipment sound profi les 

and worker task observations where possible. 

Scope of research 

Background. Noise surveys were conducted at nine 

sand and gravel operations, including three surface pits, 

five dredges and eight processing plants. Three dredges 

were mechanical navigation dredges (river-based, also 

known as hoist boats) that employ a crane and clam 

bucket to remove river bottom material, and two dredges 

were electric hydraulic cutter head mining dredges (landbased) that employ a rotating cutter head and suction to 

remove the sand material from the pit. Table 1 lists the 

specific characteristics of each operation. The operations 

were located in Arizona, New Jersey and Pennsylvania. 

In total, dosimetry for 75 workers (MSHA PELs) and 101 

equipment noise profiles were completed. Noise doses 

were recorded for equipment operators, crushing plant 

operators, crusher operator, dredge/crane operators, boat 

pilots and deck hands, technicians, mechanics and laborers.The equipment noise profiles included stationary and 

mobile mining equipment, control rooms, dredges, cranes, 

towboats and crushing and screening facilities. In addition, the mobile equipment was monitored for noise 

inside and outside the cabs to determine the effectiveness 

of the cabs at protecting the operators from engine and 

operational noise. 

Instrumentation and data collection. The instrumentation used in the studies included personal dosimeters 

and sound level meters (SLM). Worker noise-exposures 

were monitored using Quest Q-400 Noise Dosimeters.1 

Workers donned dosimeters for their full work shifts.The 

microphone was located at the middle of the shoulder per 

MSHA recommendations (MSHA 2000). The dosimeter 

was set to monitor an MSHA PEL of 100 percent or a 

TWA8 of 90 dB(A) (specific parameters of this setting include: A-weighting, 90-dB threshold and criterion levels, 

5-dB exchange rate, slow response and a 140-dB upper 

limit). 

Equipment and area sound levels were recorded using a Quest Model 2900 SLM and a Brüel & Kjær 2260 

FIGURE 1 

Distribution of sand and gravel operations in the United 

States.

 

 

 

 

 

 

 

 

 

 

 

Table 1 

Characteristics of sand and gravel operations surveyed. 

Dredge Location Type Product 

S&G1 Land Pit Sand and gravel 

S&G2 Land None1 Sand and gravel 

S&G3 River Dredge, Crane Sand and gravel 

S&G4 Land Pit Sand and gravel 

S&G5 Land Dredge, Suction Primarily sand 

S&G6 Land Dredge, Suction Primarily sand 

S&G7 Land Pit Sand and gravel 

S&G8 River Dredge, Crane Sand and gravel 

S&G9 River Dredge, Crane Sand and gravel 

Approximate 

Processing production, Number of 

facilities st/yr employees 

Land, Both2 1,000,000 25-30 

Land, Wet 400,000 7 

On Board, Wet 350,000 14 

Land, Dry 120,000 7 

 Land, Wet 1,200,000 11 

 Land, Wet 400,000 10 

Land, Wet 180,000 7 

Land, Wet3 200,000 25 

Land, Wet 140,000 9 

1

None – No mining occurred at this site. Material for processing is trucked from two off-site pits.
 

2

Both – Material processed both dry and wet.
 

3

Land-based processing facilities were not surveyed at this site.
 

Investigator. The SLM and Investigator were mounted 

side-by-side on a tripod, with the microphone located 

1.5 m (5 ft) from the floor/ground (approximately ear 

height), angled at 70o from the source (per manufacturer 

recommendations) and facing the sound source. Measurements were made on a 1- to 2-m (3- to 6-ft) grid, at 

a distance of approximately 1 to 2 m (3 to 6 ft) from the 

equipment. Measurements were made to delineate the 

near-field and far-field equipment sound levels. An Aweighted equivalent sound pressure level (Leq) was recorded at each location. The parameter of interest for 

these studies was the average integrated sound level accumulated during a specified measurement period or Leq 

using a 3-dB exchange rate. The 3-dB exchange rate is 

the method most firmly supported by scientifi c evidence 

for assessing hearing impairment as a function of sound 

level and duration (NIOSH, 1998). A slow response rate 

with an averaging time of 10 seconds was employed, with 

most readings being recorded during a 30-second period. 

Measurements made around the cranes (dredges) and 

1

 Reference to brand names does not imply endorsement by 

NIOSH. 
52 MARCH 2008 MINING ENGINEERING

 

 

 

 

 

processing facilities were used to generate sound profi le 

plots. Although sound is a logarithmic quantity, the plots 

were generated linearly. It is believed that linear sound 

profile plots are adequate for describing the sound levels around mining equipment solely for the purpose of 

alerting mine workers of areas to avoid, minimizing their 

noise exposures. 

FIGURE 2	 

Example of dosimeter outside mobile equipment. 

FIGURE 3 

Navigational dredge with on-board processing. 

Results 

Worker noise exposure. Workers at each site wore 

dosimeters for a full shift to provide noise exposure data. 

When two production shifts were used, workers on both 

shifts were surveyed. Table 2 lists the worker dose levels 

that were measured, including the inside/outside cab dose 

levels for evaluation of cab effectiveness in preventing 

exposure to engine and equipment operation noise. A 

typical dosimeter location for outside cab measurements 

is shown in Fig. 2. 

Two general conclusions can be made from these data. 

First, all worker doses were below the MSHA PEL of 100 

percent (0.19 percent to 90.02 percent, Table 2). There 

were two workers, a plant man and a belt picker, who 

accumulated dose levels around 90 percent. The plant 

man was responsible for cleaning around the processing equipment, including while the plant was operating. 

Much of the equipment generates sound levels greater 

than 90 dB(A), thus this worker’s noise dose was not 

unexpected. The belt picker worked on the dredge that 

utilized on-board processing. The worker was located in 

a crudely built shanty located next to the belt carrying 

material from the grizzly to the processing facility. This 

worker’s job was to pick wood and other debris from 

the belt. Because the shanty had little if any noise controls in place, the picker was subject to the sound levels 

generated by the nearby processing equipment. Again, 

his measured dose was not unexpected. Secondly, a comparison of the interior and exterior mobile equipment 

dose levels indicates that the equipment cabs provided 

 

MSHA PEL noise dose for sand and gravel workers.

 Worker Outside cab

 Number range of range of 

 of recorded MSHA PEL of MSHA PEL 

Job title doses dose, % dose, % 

FEL operator 17 0.19-51.83 27.21-244.31 

Laborer/utility man 7 16.81-63.05 ND2 

Dredge operator/trainee (CR1) 7 2.32-10.74 ND 

Plant operator (CR) 6 1.72-10.45 ND 

Plant man 6 28.79-90.02 ND 

Crane operator 6 3.06-26.36 48.20-109.81 

Haul truck operator 5 10.32-50.27 63.12-121.99 

Boat pilot 4 8.58-43.58 ND 

Crusher operator 3 3.66-41.20 ND 

Technician 3 0.83-15.39 ND 

Shopman/maintenance man 3 5.95-38.56 ND 

Belt picker 2 23.71-89.96 ND 

Dredge oiler 2 8.67-11.27 ND 

Water truck operator 2 14.6-59.13 ND 

Deck hand 1 4.74 ND 

Scale man 1 1.67 ND 

1

CR = Control room 

2

ND = Not determined 

Table 2 
sufficient protection from noise for the operators. The 

front-end loader (FEL), crane and haul-truck operators 

all had MSHA PEL noise dose levels below 52 percent, 

yet the outside dose levels were as high as 245 percent. 

This illustrates that the cabs were protecting the operators from equipment operational noise. 

 

FIGURE 4 

Sound profile plot for a navigational dredge with onboard processing. 

FIGURE 6 

Sound profile plot for a navigational dredge without onboard processing. 

FIGURE 5 

Navigational dredge without on-board processing. 

MINING ENGINEERING MARCH 2008 53

FIGURE 7 

Electric hydraulic cutter head mining dredge. 

Equipment/area noise measurements. Sound-level 

measurements were taken around all stationary equipment, such as the conveyor belts and conveyor belt 

drives, crushers, screens, cranes, towboats and mobile 

equipment, including front-end loaders and trucks. 

Table 3 lists the results of the sound level measurements for both the processing equipment and dredges. 

For convenience, equipment such as screens, crushers 

and belt drives are combined by category, even though 

they varied widely in size and product throughput. 
54 MARCH 2008 MINING ENGINEERING

The sound levels varied widely because of the size and 

throughput just mentioned, because of equipment age 

and condition and because the ranges include measurements taken at varying distances from the stationary equipment. 

FIGURE 8 

Sound profile plot for and electric hydraulic cutter head 

mining dredge. 

FIGURE 9 

AC51 cone crusher. 

FIGURE 10 

Sound profile plot for AC51 cone crusher. 

FIGURE 11 

Primary triple-deck screen. 

Dredges. To illustrate the sound levels measured on 

the dredges, several examples are included. Figures 3 

and 4 include a photograph and sound profi le plot of 

the sound levels on a mechanical navigation dredge 

with on-board processing. Figure 4 illustrates that outside the diesel engine room is the noisiest, but also that 

the barge areas containing the processing equipment 

have sound levels above 90 dB(A). 

Figures 5 and 6 include a photograph and sound 

profile plot of the sound levels on a navigational 

dredge that dumps material directly into barges. Figure 

6 illustrates that, in general, the noise levels are below 

90 dB(A). Noise levels above 90 dB(A) were recorded 

in the crane engine room and diesel engine room. 

Figures 7 and 8 include a photograph and sound 

profile plot of the sound levels on an electric hydraulic 

cutter head mining dredge, with an underwater suction pump and a cutter basket that extracts sand from 

the bottom of the pit, then pumps the sand/water mix 
back to the processing facilities. Figure 8 illustrates 

that the sound levels are generally below 90 dB(A), 

except near the freshwater pumps and the DC electric 

motor driving the underwater suction pumps at the 

rear of the dredge. The sound-level measurements on 

all the dredges indicate the areas where exposure to 

noise should be limited (near the diesel engines of the 

barge and crane and on-board processing facilities) 

and where overexposures could be minimized (control 

room, offices, and crane operators cab). 

,

dB(A)1

 Crane, operators cab 

 Crane, engine room 

Offi ce, tool room, misc. rooms 

 Diesel motor 

Inside 

Inside 

Inside 

Inside 

76-85

 102-107

64-89

 103 

Dredge Barge area 

 Control room 

Outside 

Inside 

64-102

 66-76

 Control room Outside 69-84 

Suction pump drive motors 

 Hydraulic pump room 

 Electrical room 

Outside 

Inside 

Inside 

83-96

 98

 92

 Pilothouse Inside 67-74

 Deck Outside 75-100 

Towboat Auxiliary rooms 

 Engine room 

Inside 

Inside 

76-83

 110

 Crane, operators cab 

 Crane, engine room 

Crushers 

Inside 

Inside 

Area 

82-88

 92-107

 81-112

 Control rooms Inside 56-79

 Control rooms Outside 73-83 

Plant Screens Area 77-108

 Cyclones 

 Belts, drives, transfers 

Sand classifiers 

Area 

Area 

Area 

81-88

 62-95 

76-89

 Misc. buildings, trailers 

 Scale house 

Inside 

Inside 

51-89

 51-72

 Sand screws Area 81-88

 Plant area noise Ground level 61-97	 

1

Measured with a 3-dB exchange rate.	 

MINING ENGINEERING MARCH 2008 55

 

 

FIGURE 12 

Sound profile plot for primary triple-deck screen. 

Towboats. At the three river-based dredges towboats were used to move the loaded and empty barges 

between the dredge and processing plants/storage yard. 

Because these towboats generally push only one barge 

at a time, they are small by comparison to the towboats 

that normally ply the rivers around Pittsburgh, PA. 

Table 3 includes the range of sound levels measured 

on the towboats. The measurements revealed that the 

pilothouses were quiet (<74 dB(A)), the diesel engine 

rooms were noisy (110 dB(A)), and the deck area was 

quiet (< 80 dB(A)), except near the engine rooms and 

exhaust mufflers (100 dB(A)). 

 

 

 

 

Table 3 

Sound level measurement at sand and gravel sites surveyed.

Area Equipment Location 

 Leq range

Processing plants. The processing-plant equipment 

consisted of screens, crushers, conveyor belts, cyclones, 

sand classifiers and screws, miscellaneous buildings 

(shops, electrical, compressor, etc.), cranes and control 

rooms. In addition, front-end loaders and haul trucks 

were used at the surface sand and gravel operations and 

in the processing facilities. Table 

3 contains a summary of the 

sound levels measured in all the 

processing facilities. The cranes 

that removed material from the 

barges and deposited the material into a hopper had similar 

sound levels as the cranes on 

the dredges. Sound levels measured in the cabs were slightly 

higher (82 to 88 dB(A)), while 

the engine room sound levels 

were nearly identical (up to 107 

dB(A)). Based on these results, 

it is recommended that as little 

work as possible should be done 

in the crane engine rooms while 

operating. 

An Allis-Chalmers (AC51), 

1.8-m- (6-ft-) diameter cone 

crusher is illustrated in Fig. 9.The 

sound profile plot for this crusher 

is shown in Fig. 10 and reveals 

that sound levels approaching 100 

dB(A) were present.An example 

of an older screen that is processing river dredged sand and gravel 

is illustrated in Fig. 11.The sound 

profile plot for the primary triple-deck screen is shown in Fig. 

12 and reveals that sound levels between 105 and 110 dB(A) 

were present. Two screens, processing primarily sand, are shown 

in Fig. 13. The fact that they are 

processing sand and small gravel 

and using urethane screen cloth 

to control noise, keeps the sound 

levels generally below 90 dB(A) 

(Fig. 14). Finally, Fig. 15 illustrates 
56 MARCH 2008 MINING ENGINEERING

the sound levels for an entire plant. In general, the sound 

levels are below 90 dB(A) except in the area around the 

No. 1 primary screen and 1.5-m (60-in.) crusher. 

FIGURE 13 

Diester 1.8- x 6.1-m (6- x 20-ft) shaker screens. 

FIGURE 14 

Sound profile plot for Diester 1.8- x 6.1-m (6- x 20-ft) 

shaker screens. 

FIGURE 15 

Sound profile plot for entire plant. 

Discussion 

Considering the high noise levels that the mining, 

dredging and processing equipment generate, the large 

number of sand and gravel operations in the United 

States and the more than 45,000 employees, the concern 

for preventing NIHL is significant. Sound levels as high as 

112 dB(A) were recorded near crushers, 108 dB(A) near 

screens, 107 dB(A) in the engine rooms of the cranes and 

up to 97 dB(A) in the plant areas. Over time, exposure 

to these noise levels for even short durations could result 

in permanent hearing loss. Fortunately, the results of this 

research effort indicate that workers are avoiding high 

noise areas as revealed by the relatively low dose levels 

recorded. In general, all but three of the doses recorded 

were less than 60 percent with only two approaching the 

MSHA PEL of 100 percent (89.96 percent and 90.2 percent), as shown in Table 2. 

Because most employees are in cabs or control rooms, 

they are protected from noise overexposure, as illustrated by the results of the dose measurements. For those 

workers who must spend time in the 

processing plants and engine rooms, 

it would be prudent to restrict time 

spent in and around the screens and 

crushers in the plants and the pumps 

and motors on the dredges and to 

require mobile equipment operators to keep all doors and windows 

closed while the equipment is in operation.All workers should be made 

aware of the sound levels around 

all equipment and in the plants and 

dredges and should be instructed 

to use hearing protection based on 

NIOSH’s recommended exposure 

limit (REL) of 85 dB, A-weighted, 

as an 8-hour time-weighted average 

(TWA8) (NIOSH, 1998). Exposures 

at or above this REL are hazardous, 

creating an excess risk of developing occupational NIHL. For workers whose noise exposures equal or exceed 85 dB(A), 

NIOSH recommends proper use of hearing protection, 

among other assessment, training and prevention approaches. Any area that has a sound level of 85 dB(A) 

or higher has the potential to exceed the NIOSH REL 

depending on the exposure time. Because the length of 

exposure can vary and/or is not known prior to entering a high sound area, the potential adverse effects on 
MINING ENGINEERING MARCH 2008 57

 

a worker’s hearing are also not known, thus it makes 

sense to use hearing protection when in areas where the 

sound levels are 85 dB(A) or greater. 

The sound level measurements on all the dredges 

indicate that workers should limit their exposure near 

the diesel engines of the barge and crane, and on-board 

processing facilities. Similarly, on the towboats, the 

diesel engines are noisy and should be avoided when 

possible. When it is necessary to be near the engines, 

workers should wear appropriate hearing protection. 

In addition, based on the measured sound levels, it is 

recommended that as little work as possible should be 

done in the crane engine rooms while they are operating. 

It is also important that hearing-protection devices 

(HPDs) are used in high noise areas, even though workers are limiting their exposures as evidenced by the lack 

of MSHA PEL doses over 100 percent. Finally, HPDs 

are only a temporary substitute for effective engineering and administrative noise controls. Noise-induced 

hearing loss will be eliminated only through a coordinated effort of applying noise controls and HPD use for 

exposure reduction. 

Disclaimer

The findings and discussions in this report are those 

of the authors and do not necessarily represent the 

views of the National Institute for Occupational Safety 

and Health. 

References

Federal Register, 1999, Health Standards for Occupational Noise Exposure: Final Rule, Department of Labor, Mine Safety and Health Administration, 30 CFR Parts 56 and 57 et al., Vol. 64, No. 176, Sept. 13, pp. 

49548-49634. 

Landen, D., Wilkins, S., Stephenson, M., and McWilliams, L., 2004, 

“Noise exposure and hearing loss among sand and gravel miners,” Journal 

of Occupational and Environmental Hygiene, Vol. 1, pp. 532-541, August. 

Mine Safety and Health Administration (MSHA), 2000, “Sampling 

for Silica and Noise-A Handbook for Metal/Nonmetal Miners and Mine 

Operators,” U.S. Department of Labor, Instruction Guide Series, IG 29, 

27 pp. 

National Institute for Occupational Safety and Health (NIOSH), 

1996, “Analysis of audiograms for a large cohort of noise-exposed miners,” Franks, J.R., pp. 1-7, and cover letter to Davitt McAteer from Linda 

Rosenstock, Aug. 6, 1996. 

National Institute for Occupational Safety and Health (NIOSH), 1997, 

“Prevalence of hearing loss for noise–exposed metal/nonmetal miners,” 

Franks, J.R., pp. 1-5, and cover letter to Andrea Hricko from Gregory Wagner, Oct. 7, 1997. 

National Institute for Occupational Safety and Health (NIOSH), 1998, 

“Criteria for a Recommended Standard: Occupational Noise Exposure,” 

Revised Criteria. DHHS (NIOSH) Pub. No. 98-126, National Institute for 

Occupational Safety and Health, Cincinnati, OH, p. 25.