Noise assessment of 

stone/aggregate mines: 

six case studies 

Tntrodustion LR. '&AUER AN! 1.1. BAII~H number of ways, including condnctExposure tq noise and noisefa- ing a cross-sectional survey of noise 

dnced hearing loss (NEL) contin- sources and worker noise exposures 

URS to be problematic for the U.S. in the mining industry. Initially, these 

mining industry. The pmblem is par- surveys were conducted in surface 

ticdarly severe because large, noisy and underground (continuous and 

equipment dominates the industry, longwall) coal mines, in coal prepaStudies have shown that 70 percent ration plants and in sand md gravel 

to 90 percent of all miners have mines. Recently, this has included 

NE great enough to be daqsified as a hearing disability surve~hg stone (aggregate) &ing and crushing and 

(WOSH, 1996),% address the issrre,ae U.S. me Safety processing hcdities. The mine sites were selected primamd Health Administration (MSHA) published Health ily th.rQugh ~emaal contacts within ffie mining industry. 

Standards for Occupational Noise Exposure (Federal Participation fie surveys was voluntary for mine 

Re@&-', 1999). The new regulations include: the adop- sites, but 100 percent of the mines contacted participated. 

tion of a hearing-conservation program similar to that of the SuweYs were completed between May and Octhe US, Occupational Safq Health Adhiswation tober 2005. The surveys are designed to monitor worker 

(QS~), *th an 'xction hvep of 85 ~B(A) eight-hour dose, to measure equipment sound levels and ta undertfmc weighted average ('A81 and a permissible expo- stand the noise sozrrcelworker dose relationship. This 

I s- level (pEq of 90 &(A) TWAg.me regulations also is accomplished through full-shift dosimetry readings. 

state that a miner3 noise exposure shall not be adjusted eq~ipme~t noise Profiles and, where possible, worker 

because of the use of personal hearing protection, and task ~I~en~atiQfisthat all feasible engineering and administrative controls 

must be used for noise exposure ~eduCti~n. I The W.S. National Institute for Occqxitional Safety Instrumentation and data ~ollection 

I and Health (NIOSH) has responded to this problem in a Sound levels in th t mines and processing facilities 

were measured using a Quest Model 2900 sound levd 

meter (SLM) and Briiel& Kim 2260 Investigator. The inAisi!rarct 

The U.S. Natioraal Instit~te for Occupario~lal Safm and 

Health (NIOSH) Lz conducting a cross-sectional survey 

qf equipment sound levels and worker nobe exposures in 

the sbondaggregate mining industry. Six standaggregate 

minm (three s~rfoce and three wtdergsound) were recently 

surveyed, and the findings are presented hre. The surveys 

cocensisted of sound-level memuremmts cond~cted around 

VC~~~OUS eq~,Gpme~t atd rnachepJ (incllkdhg srorze p roceming and crushing equipment) and fill-shift dose memuremeptts to detmine worker norlce apnsures. The fndings 

identifjl the equipment mQ machiney thor are likely to 

cause worker overexposures and idm~fy the workemfomd 

to toe experiencing overep oO~tk.res. addition, the bene$t 

I of cabs in reducing mobile equipment operator noise exexpornre i~ dhcussed. 

stm&ts wkre mounted sidkby side on a hibod, with the 

microphones 1.5 m (5 ft) from the floor (appro-ately 

ear height), angled at 70" from horizontal (in accordance 

with manufacturers' ~ecommendations) and facing the 

noise source. An A-weighted equivalent sound pressure 

level (Lea and one-third linear octave band frequencies 

were recorded at each localion. Leq, which for these studies .was the parameter of intesest,is the average integrated 

sound level accumulated during a specified measurement 

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

rate is the method most My supported by scientific evidence for assessing hearing impairment as a function of 

noise level and duration (NXOSH, 1998).A dow response 

rate with an averaging be (Iength of measurement) of 

30 seconds was also employed. Measurements were made 

around the fans. stationary equipmen.t and processing 

facilities. Both near and far field measurements were recorded. The term "'near" describes measurements made 
56 August 2007 Mining EnginEEring

Figure 1	 of cabs to prevent operator noise exSound profile plot for the primary screening tower.	 posure from engine and operational 

noise. 

Case studies 

Case study No. 1 — surface

limestone mine 

Mine characteristics: This study 

site consisted of one surface pit and accompanying rock processing facilities 

that mine and process approximately 1.13 Mt (1.25 million st) annually 

of crushed stone and lime products. 

Mining consists of bench drilling and 

blasting (by a contractor), and mining 

the limestone rock.The blasted rock is 

mined using front-end loaders (FELs) 

loading into 45.4-, 49.9- or 54.4-t- (50-, 

55- or 60-st-) capacity haul trucks for 

removal from the pit. The haul trucks 

dump into a primary crusher located 

near the pit entrance. After passing 

through the primary crusher, the rock 

is transported by belt to the crushing 

and screening facilities, resulting in the 

desired product sizes. The daily mining and processing operations average 5.44 to 6.35 kt (6,000 to 7,000 st) 

within 1 to 2 m (3 to 6 ft) of the noise source while the 

“far” measurements were those taken farther than 2 m (6 

ft) from the source. 

Worker noise exposure was monitored using Quest 

Q-400 noise dosimeters.The dosimeters were set to monitor an MSHA permissible exposure level (PEL) of 100 

percent or an eight-hour time-weighted average (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.) Where possible, noise dose was recorded inside 

and outside mobile equipment to determine efficiency 

Figure 2 

of rock.Approximately 25 workers are 

located in the surface quarry, and 10 are located in the 

plant (crushing facilities). The worker classifications include FEL operator, haul-truck operator, primary crusher 

operator, control-room operator, plant operator, plant 

helper laborer and water-truck operator. 

Equipment and plant sound levels: Table 1 lists the 

range of sound levels measured around various processing equipment and indicates that the sound levels varied 

greatly throughout the plants. The highest sound levels 

were recorded at the primary screening tower, surge tunnel, secondary crusher, secondary screening tower and 

the fourth level of the agricultural lime 

crusher. Most of the recorded readings 

were 93 dB(A) or less.A sound profile 

Sound profile plot for Telsman screens 2 and 3.	 plot for the primary screening tower is 

illustrated in Fig. 1.The measurements 

ranged from 87 to 96 dB(A) outside 

the building and 105 to 107 dB(A) inside the screening tower. 

Worker exposure: Worker noise 

exposure was collected using dosimeters worn by the workers for the 

full (10-hr) shift. Six occupations that 

were surveyed included the operators 

of haul trucks, front-end loaders, primary crusher and the control rooms. 

Plant helpers and operators were also 

monitored. Results of the worker dose 

measurements are shown in Table 2. In 

addition to worker dose, a dosimeter 

was placed outside the cab on the front 
Mining EnginEEring August 2007 57

end loaders (FEL) and Table 1 

on the haulage trucks. 

This provided the exposure that would occur 

Sound level measurements, case study No. 1, surface limestone. 

Range Leq,

without the protection Plant Equipment Location dB(A) 

of cabs. Although the 

mining and processing 

equipment sound level Primary screening tower B(N) Inside 105-107 

measurements suggest Primary screening tower B(N) Outside 87-96 

that there were areas Primary surge tunnel, surge to sec. crusher In tunnel 88-101 

that are noisy and work- secondary secondary crusher Ground level 89-93 

ers could be over-ex- secondary secondary crusher Upper level 97-99 

posed to noise, because secondary Compressor bldg. Inside, door open 89 

the workers are in cabs secondary Compressor bldg. Inside, door closed 90 

or control rooms, all the secondary Compressor bldg. Outside 91 

workers that were moni- secondary 152.4 cm (60 in.) hydrocyclone crushers Ground level 82-90 

tored experienced doses secondary 152.4 cm (60 in.) hydrocyclone crushers Upper level 84-95 

well below the MSHA secondary Control room Inside control room 72 

PEL of 100 percent (or secondary screening tower e(N) Inside 100-106 

a TWA of 90 dB(A)). ag Lime screening tower and control room second level 86-99 

ag Lime screening tower and control room Third level 90-93 

Case studies No. 2 ag Lime screening tower and control room Fourth level 91-93 

and No. 3 — surface ag Lime screening tower and control room Inside control room 65 

granite mines ag Lime screening tower and control room Fifth level 91-92 

Mine characteristics: ag Lime screening tower and control room sixth level 91-93 

This complex consisted ag Lime screening tower and control room seventh level 91 

of two surface pits and ag Lime Crusher Ground level outside 76-90 

rock processing facilities ag Lime Crusher second level 87-89 

that mine and process ag Lime Crusher Third level 88-89 

approximately 1.36 Mt ag Lime Crusher Fourth level 81-102 

(1.5 million st) annually ag Lime C3 belt tunnel Inside 77-88 

of crushed stone products. Mining consists of Quarry Primary crusher Inside control room 67 

contractor-completed Quarry Primary crusher Outside 72-95 

bench drilling and blasting, and mining of the Primary Primary plant area (No. 71,72,74) 74-79 

granite gneiss rock. The secondary secondary plant area (No. 64-70,83,84) 72-81 

blasted rock is mined ag Lime ag lime plant area (No. 73,75-82) 67-83 

using front-end loaders (FELs) loading into 

36.3-t- (40-st-) capacity haul trucks for removal from the buildings and at the primary crusher. Table 3 lists the 

pit. The haul trucks dump into a primary crusher located results of the sound-level measurements around the 

near each pit.After passing through the primary crusher, stationary equipment and indicates that the sound levthe rock is transported by conveyor belt to the crushing els varied greatly throughout the plants. The locations 

and screening facilities, resulting in the desired prod- where high sound levels (greater than 90 dB(A)) were 

uct sizes. Approximately 33 workers are located at the recorded included the screens and crushers in Plant A, 

combined surface quarries and crushing facilities. The the screening tower and primary crusher in Plant B and 

worker classifications involved in the mining and process- the screen, crusher and tunnel in Plant C.An example of 

ing operations include 

operators of FELs, haul Table 2 

trucks, primary crusher 

and processing plant. Worker exposure, case study No. 1.

 Worker range Outside cab range

E q u i p m e n t a n d Number of MSHA PEL dose, MSHA PEL dose, 

plant sound levels — Occupation recorded doses % % 

Case study No. 2: The 

processing facilities Haul truck operator 3 2.7-14.8 65.9-114.1 

consisted of three sta- FeL operator 3 0.7-41.3 59.0-65.6 

tionary plants (A, B and Primary crusher operator 1 13.4 Na 

C). Measurements were Plant operator 1 0.9 Na 

taken around transfer Plant helper 3 17.5-33.4 Na 

points, belts, crushers ag lime control room operator 1 8.2 Na 

and screens, control 

rooms, miscellaneous Na = not applicable 
58 August 2007 Mining EnginEEring

Figure 3	 side the cabs of the mobile equipment. 

Table 4 lists the worker doses for the Sound profile plot for portable plant.	 employees at the site. No worker experienced a dose above the MSHA PEL 

of 100 percent. Table 4 illustrates that 

for the mobile equipment operators, a 

reasonable amount of protection from 

the exterior noise generated by the engines and equipment operation is provided by the cabs. Only the operator of 

Truck 68 had a dose near 100 percent 

(98 percent), which was the result of 

the truck’s outside dose of 396 percent 

and some unknown engine, transmission or exhaust noise problem that was 

able to enter the cab. 

Equipment and plant sound levels – Case study No. 3: Measurements 

were taken in the plant known as the 

portable plant. Forty-six sound level 

measurements were taken around 

the transfer points, belts, crushers and 

screens, the control room and the primary pit crusher.Table 5 lists and Fig. 3 

illustrates the results of the sound-level measurements around the station- the sound levels measured is illustrated in Fig. 2, which ary equipment. The data indicate that the sound levels 

is the sound profile plot for screens 2 and 3 in Plant A. varied greatly throughout the portable plant. The loca- Sound levels from 88 to a little more than 100 dB(A) tions where high sound levels (greater than 90 dB(A)) were recorded. were recorded included Screens S1 and S2 and Crushers 

JCr1 and CrLJ54. 

Worker exposure – Case study No. 2: Workers wore 

dosimeters for a full shift (10 to 10.5 hrs) to provide Worker exposure – Case study No. 3: Workers wore 

noise-exposure data. Dosimeters were also placed out- dosimeters for a full shift (9.5 to 10.5 hrs) to provide 

noise exposure data. Table 6 lists the Table 3 worker doses for the employees at the 

Sound level measurements, case study No. 2, surface granite. site. No worker experienced a dose above 

Range Leq, the MSHA PEL of 100 percent. Table 6 

Plant equipment Location dB(A) illustrates that, for the mobile equipment 

operators, the cabs are providing suffia Belts, transfer points, bins Ground level 78-91 cient protection from the exterior noise 

Crusher CrT57 Outside 94-97 generated by the engines and equipment 

Crusher CrLJ45, eljay Outside 98-99 operation. 

screen #s2, Telsman Outside 88-99 

screen #s3, aeI Inside 100-102 

Ortner wash plant, W1 Outside 81-85 Case studies No. 4 and No. 5 — 

Control room Inside 74 underground limestone/sandstone 

Control room Outside 93 mines 

Mine characteristics: This operation 

B Belts, transfer points, bins Ground level 72-88 consists of two underground mines and a 

screening tower, screen #s1 Inside 98-112 common rock processing facility. Mining 

Primary jaw crusher, B JCr1 Outside control room 93 consists of face drilling, shooting and minPrimary jaw crusher, B JCr1 Inside control room 75 ing the main limestone bench, followed 

Primary jaw crusher, B JCr1 Lower levels 88-105 by drilling, shooting and removing the 

electric room Inside 58 limestone floor rock. In addition, in some 

Oil and pump room Inside 64 areas, the sandstone below the limestone 

is also mined. The blasted rock is loaded 

Belts, transfer points, bins Ground level 75-96 by front-end loader into 45.4- or 54.4-tCrusher CrT52 Outside 99-102 (50- or 60-st-) capacity haul trucks for 

screen #s6 Outside 85-94 removal from the mine. The haul trucks 

electric room Inside 68 dump into one of two primary crushers, 

Tunnel, C10B belt Inside tunnel 85-97 which are located midway between the 

two mines’ portals. After passing through 

C 
Mining EnginEEring August 2007 59

the primary crusher, the Table 4 

rock moves by conveyor 

belt either to the secondary crushing facilities or 

directly to a stockpile 

for loading and sale to 

Number of

Occupation recorded doses

Worker exposure, case study No. 2.

 Worker range 

MSHA PEL dose, 

% 

Outside cab range

MSHA PEL dose, 

% 

end users. Rock sent to 

the secondary crushing 

facility passes through 

a series of crushers and 

screens, resulting in the 

Haul truck operator (65,66,68)

FeL operator (27,32,34)

Primary crusher operator (B J Cr1) 

Bin truck operator (7)

 3 

3 

1

 1

3.0-98.0

0.4-28.3

 2.0 

10.2

 111.0-396.1 

33.0-284.8 

Na 

22.2 

desired product sizes. 

The combined annual Na = not applicable 

production from both 

mines is about 1.36 Mt 

(1.5 million st) of mostly crushed limestone and some ployees. In all cases, except one of the laborers, no worker 

sandstone. A total of 43 workers are located at the site, experienced a dose above the MSHA PEL of 100 percent. 

The one laborer experienced a dose above 100 percent 

working two shifts per day. The worker classifications because he was operating an air wrench while installing include operators of FELs, haul trucks, jaw crusher, drill, 

scaler, plant and water truck. Other classifications include 

sheet metal on the protective canopy at the entrance to 

supervisor, mechanic, blaster and blaster helper, laborer mine No. 2. His exposure resulted from a combination of 

and utility man. noise sources that included the air wrench, compressor and 

Figure 4

Equipment and plant sound levels: Measurements 

were taken around the main and auxiliary fans, primary JOY Axivane 18.6 kw (25-hp) fan (Bauer and Babich, 

jaw crushers (old and new), semi-stationary equipment 

and near the crushers and screens located at the secondary crushing facilities. Table 7 lists the results of the sound 

level measurements around the stationary and semi-stationary equipment and indicates that in most locations, 

sound levels greater than 90 dB(A) were present. The 

highest sound levels were recorded near the fans and the 

No. 1 cone crusher located in the secondary crushing plant. 

The only locations where sound levels were consistently 

less than 90 dB(A) were in the primary crusher operator’s 

control booth, in the secondary crusher operator’s control 

room, in the electrical room below the secondary crusher 

control room and above the sand plant. 

The underground face equipment included a Tamrock 

floor drill and Cannon face drill (both 

diesel) and a Gradall scaler. Sound levels Table 5 

around these three pieces of equipment Sound level measurements, case study No. 3, surface granite.


were high, ranging from 89 to 103 dB(A). Range Leq,
 However, the sound level measured in- Plant Equipment Location dB(A)


side the enclosed cab of the Cannon face 


drill was only 83 dB(A). Figures 4 and 5 Portable Belts, transfer points, bins Ground level 77-94


include a photograph and a sound profile Crusher CrLJ55, el-Jay Outside 92-97


plot of a JOY Axivane 18.8 kw (25-hp) screen #s1 Outside 88-91


fan.The sound levels near the fan ranged screen #s2 Outside 97-104


from 90 to 106 dB(A).Another example Primary crusher, P JCr1 Outside 88-92


is illustrated in Figs. 6 and 7, which are a Control room Inside 71


photograph and sound contour plot for 


a Tamrock Ranger 500 floor 


drill. Figure 7 illustrates that Table 6


sound levels up to 102 dB(A) Worker exposure, case study No. 3. were recorded near the drill. Worker range Outside cab range

Worker exposure: Work- Number of MSHA PEL dose, MSHA PEL dose, 

Occupation recorded doses % %

ers at the mine wore dosimeters for a full shift (10 to Haul truck operator (69) 1 11.7 118.2 

10.5 hrs) to provide noise ex- FeL operator (24, 25) 2 13.5-25.4 154.4-159.0 

posure data. Table 8 lists the Primary crusher operator (P J Cr1) 1 20.4 Na 

worker doses for both surface and underground em- Na = not applicable 
60 August 2007 Mining EnginEEring

Figure 5 mobile equipment entering and exiting the mine. Table 8 

also illustrates that for the mobile equipment operators Sound profile plot for Joy Axivane 25-hp fan. the cabs are providing a reasonable amount of protection from the exterior noise generated by the engines and 

equipment operation. 

Case study No. 6 — underground limestone mine 

Mine characteristics: This operation consists of an 

underground mine and surface rock-processing facilities. 

Mining consists of face drilling, shooting and mining the 

main bench, with some mining of the floor rock. Using 

front-end loaders, the blasted rock is loaded into 31.8-t- 

(35-st-) capacity haul trucks for transport from the mine 

to the primary crusher.After passing through the primary 

crusher, the rock is transferred by belt to the crushing 

facility consisting of a shaker, screen and/or cone crusher 

to obtain the desired product sizes. Annual production 

for this operation is about 317.5 kt (350,000 st). From 10 

to 12 workers are located at the site, working one shift per 

day. The worker classifications include the operators of 

FELs, haul trucks, crusher, drills, scaler and water truck. 

Other classifications include mechanic and blaster and 

blaster helper. 

Equipment and plant sound levels: Measurements 

were taken around the primary jaw crusher, semi-stationary equipment and near the crushers and screens located 

at the crushing facilities. Table 9 lists the results of the 

sound-level measurements. The results indicate that a 

wide range of sound levels were present. In the mine, the 

sound levels were consistently less than 90 dB(A) around 

Table 7 

Sound level measurements, case study No. 4 and No. 5, underground limestone and sandstone. 

Range Leq, 

Mine Equipment Location dB(A)

No. 1 Fan systems 66HPaV2s, 

1.5 m (5 ft) aux. fan 15 mains at 25 XCut 88-104 

No. 1 Main fan (1.5 m (5 ft exhaust)) 17 XCut in B mains 75-84 

No. 1 Joy M96-50D exhaust fan G mains at 24 XCut 86-109 

No. 1 Tamrock ranger 500 floor drill 19 XCut in 9 mains 91-102 

No. 2 Main fan (3.7 m (12 ft intake)) 7 Mains 95-101 

No. 2 Main fan (2.4 m (8 ft exhaust)) 1 XCut, in 1 main 84-109 

No. 2 Joy axivane M36-26-1770 fan 5 Main at 5 XCut 90-106 

No. 2 Oldenburg cannon face drill 9 XCut in 7 mains 93-103 

No. 2 Gradall 5110 scaler 8 Mains at 5 XCut 89-98 

surface Old jaw crusher (outside) Outside control booth 83-102 

surface Old jaw crusher (inside control booth) Inside control booth 82 

surface New jaw crusher (outside) Outside control booth 84-102 

surface New jaw crusher (inside control booth) Inside control booth 74 

sec. Crusher No. 1 cone crusher (2.4 m (8 ft Nordberg)) Bottom of main belt 101-107 

sec. Crusher No. 2 cone crusher (2.4 m (8 ft)) Below main screen 99-101 

sec. Crusher No. 3 cone crusher (symons portable) adjacent to No. 2 crusher 95-98 

sec. Crusher No. 4 lower crusher (1.8 m (6 ft)) Middle of sec. crush. plant 90-96 

sec. Crusher Main 2.4 x 6.1 m (8 x 20 ft) screen above No. 2 crusher 90-99 

sec. Crusher No. 1 & 2 double screens Middle of sec. crush. plant 86-98 

sec. Crusher sand plant Bottom of sec. crush. plant 77-98 

sec. Crusher Control room (outside) Outside control room 83 

sec. Crusher Control room (inside) Inside control room 69 

sec. Crusher electrical room (inside) Below control room 75 
Mining EnginEEring August 2007 61

the bucket truck and more than 90 dB(A) near the water Figure 6 

pump, scaler and face drill. The face drill had the highest Tamrock floor drill. 

measured sound levels, ranging from 86 to 105 dB(A) 

(Fig. 8). In the processing facilities, sound levels above 90 

dB(A) were recorded nearly everywhere except in the 

jaw crusher control room and at the belt drives (Fig. 9). 

Worker exposure: Workers at the mine wore dosimeters for a full shift (9.5 to 10.5 hrs) to provide noise exposure data.Table 10 lists the worker doses for both surface 

and underground employees. In all cases, no worker experienced a dose above the MSHA PEL of 100 percent. 

Table 10 also illustrates for the mobile equipment operators that the cabs are providing a reasonable amount of protection from Figure 7 

the exterior noise generated by the Sound profile plot for Tamrock floor drill.

engines and equipment operation. 

Implications for exposure

reduction 

The sound level measurements 

suggest that there are areas that 

are noisy and could subject workers to overexposure to noise. Nearly 

all workers monitored experienced 

doses well below the MSHA PEL of 

100 percent (or a TWA of 90 dB(A)), 

even though equipment sound levels were generally above 90 dB(A). 

These exposure results do not suggest that the workers are “safe” from 

noise-induced hearing loss, only that 

the workers are limiting their time 

of exposure near these high noise 

sources. Health surveillance of hearing by use of audiometry and exposure monitoring is essential, both 

base-line and after noise exposure if 

NIHL is to be reduced in the mining 

industry. 

One laborer experienced a dose 

of 119 percent while using an air 

wrench to install a protective canopy at the portal of 

an underground mine. Mo- Table 8 

bile equipment and crusher 

operators were protected 

from overexposure to noise 

as illustrated by the results 

of the dose measurements 

 Worker range 

Number of MSHA PEL dose, 

Occupation recorded doses %

Worker exposure, case studies No. 4 and No. 5. 

Outside cab range 

MSHA PEL dose, 

% 

because the cabs and control rooms had sufficient 

acoustical treatments to 

prevent equipment sound 

levels from reaching the 

operators. Although only 

one worker was overexposed, the prevalence of 

noisy equipment suggests 

that engineering and administrative noise controls 

Haul truck operator

FeL operator

Drill operator

scaler

Crusher operator

Blaster/blaster helper

Water truck operator

Laborer

sec. crush. plant oper.

Mechanic

 6

 4

 2

 2

 1

 2

 1

 2

 1

 1

 0.6- 9.5

 2.9-64.2

 26.8-31.4

 1.1-1.20

 5.9

 27.3-28.6

 35.8

 59.0-119.3

 32.3

 8.9

 81.6-187.5 

141.7-262.8 

293.7-487.3 

187.8-209.0 

ND 

ND 

ND 

 Na 

 Na 

 Na 

could be used to reduce 

sound levels and noise ex- ND = not determined 

Na = not applicable 
62 August 2007 Mining EnginEEring

Figure 8 

Sound profile plot for Gardner Denver MK45H face drill.

Table 9 

posures. The use of acoustic material inside cabs, control 

rooms, screening towers and compressor buildings should 

be considered. Crushers and other stationary equipment 

may be addressed using mass-loaded barrier curtains 

and enclosures. Screen modifications can include acoustically treated decking and new suspension screens, as 

well. Underground fan systems should be equipped with 

silencers, muffler ducts, treated fan vanes and quiet motor 

technology (MSHA, 1999). Administrative controls such 

as job rotation, worker relocation and improved equipment operation can limit exposure to high sound levels 

and reduce worker noise exposures. 

It would be prudent to restrict time spent in and 

around the crushing and screening facilities because 

sound levels as high as 112 dB(A) were recorded. Mobile and semi-mobile (such as drills) equipment operators 

should be required to keep all doors and windows closed 

while the equipment is in operation because outside doses up to 487 percent were measured. 

All workers should be made aware of the sound levels around all equipment and in the processing plants 

and be instructed to utilize hearing protection based 

on NIOSH’s recommended exposure limit (REL) of 

85 dB, A-weighted, as an 8-hour time-weighted average 

(TWA8). 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 (NIOSH, 1998). Because 

the length of exposure can vary and/or is not known prior 

to entering a high sound area, the potential adverse efSound level measurements, case study No. 6, undergound limestone. 

Range Leq, 

Mine/surface Equipment Location dB(A) 

Mine Blaster’s bucket truck adjacent to and around 76-81 

Mine Gorman-rupp diesel water pump adjacent to and around 89-98 

Mine Gardner Denver MK45H face drill adjacent to and around 86-109 

Mine Gradall XL4300 II scaler 6.1-12.2 m (20-40 ft) away 89-94 

surface Jaw crusher (upper level) Outside control booth 91-99 

surface Jaw crusher (lower level) Below control room 89-93 

surface Jaw crusher (control booth) Inside control booth 73 

surface small Tyler double shaker screen adjacent to and around 104-111 

surface Large Tyler screen adjacent to and around 94-103 

surface Hazemag cone crusher adjacent to and around 96-102 

surface Tunnel Just inside by belt 93 

surface No. 1 belt drive Next to drive motor 89 

surface No. 2 belt drive Next to drive motor 101 

surface No. 4 belt drive Next to drive motor 85 

surface No. 6 belt drive Next to drive motor 94 

surface No. 8 belt drive Next to drive motor 85 

surface No. 9 belt drive Next to drive motor 81 

surface No. 11 belt drive Next to drive motor 82 

surface Ground level On ground 89-101 
Mining EnginEEring August 2007 63

fects on a workers hearing 

are also not known, and thus 

it makes sense to use hearing protection when in areas 

where the sound levels are 

85 dB(A) or greater. 

Finally, workers should 

realize that any exposure 

that results in an MSHA PEL 

dose above zero percent indicates that during their shift 

they encountered sound levels above 90 dB(A). Because 

each individual reacts differently to high noise, there is 

Table 10 

Worker exposure, case study No. 6. 

 Worker range Outside cab range

 Number of MSHA PEL dose, MSHA PEL dose, 

recorded doses % % 

2 38.5 and 49.7 168.7 and 175.3 

1 0.3 89.4 

1 14.3 107.2 

1 24.6 437.3 

1 50.2 162.3 

1 9.7 219.4 

2 13.3 and 15.2 0.7 

tion, http://www.msha.gov/1999noise/noiseresources.htm. 

NIOSH, 1996, “Analysis of Audiograms for a Large Cohort of 

Noise-Exposed Miners,” John Franks, National Institute for Occupational Safety and Health, Cincinnati, OH, Internal Report, 7 p. 

NIOSH, 1998, “Criteria for Recommended Standard, Occupational 

Noise Exposure, Revised Criteria 1998,” National Institute for Occupational Safety and Health, Cincinnati, OH, DHHS (NIOSH) Publication 

98-126, 105 p. 

Disclaimer 

The findings and conclusions in this report have not 

been formally disseminated by the National Institute for 

Occupational Safety and Health and should not be construed to represent any agency determination or policy. 

Occupation

Haul truck operator 

FeL operator (inside) 

FeL operator (outside) 

Drill operator 

scaler operator 

Crusher operator 

Blaster/Blaster helper 

no assurance that a dose below the MSHA PEL of 100 

percent is safe and will not cause hearing loss. In addition, when the TWA of a worker exceeds 85 dB(A), the 

MSHA Action Level is exceeded and the worker must be 

enrolled in a hearing conservation program. Therefore, 

wearing hearing protection is a good idea at all times 

while operating equipment or working in the crushing 

and screening facilities. 

Summary 

Stone (aggregate) mining can be noisy and can subject workers to overexposures if they are not in cabs or 

control rooms. Sound-level measurements indicted that 

screens, crushers, drills, fans and mobile equipment generate sound levels high enough to be potential sources 

of worker overexposure depending 

on time of exposure. Fortunately, ex- Figure 9

posure measurements revealed that 

nearly all workers were avoiding exposures as revealed by doses under 

the MSHA PEL of 100 percent. Only 

one laborer was overexposed, a result of operating an air wrench for 

much of his shift. It can be concluded 

that mine operators and workers are 

successfully avoiding noise exposures 

through a combination of training, 

hazard awareness, engineering noise 

controls and administrative noise 

controls. n

References 

Bauer, E.R., and Babich, D.R., 2006, 

“Limestone mining: Is it noisy or not?” Mining Engineering, Vol. 58, No. 10, October, pp. 

37-42. 

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. 

MSHA, 1999, “Noise Control Resource 

Guides: Surface Mining; Underground Mining; Mills and Preparation Plants,” Dept. of 

Labor, Mine Safety and Health AdministraSound profile plot of processing facilities (Bauer and Babich, 2006).