Assessment of equipment operator’s 

noise exposure in western 

underground gold and silver mines 

E.R. SPENCER 

Ellsworth R. Spencer, is research engineer, with the National 

Institute for Occupational Safety and Health (NIOSH), Pittsburgh, 

PA. 

	�

Abstract 

An assessment of U.S. western hardrock miners’ noise 

exposures was conducted as part of a multi-year National 

Institute for Occupational Safety and Health (NIOSH) 

survey of noise exposures in each sector of the mining industry.Noise from selected mining equipment and operator 

noise exposures were measured,analyzed and tabulated for 

dissemination to the participating sites and are being used 

to direct NIOSH research and interventions to address the 

greatest noise hazards. Eighty-two noise dosimeter measurements were obtained, along with time-motion studies 

as the miners operated hardrock mining machines. Of the 

operators, 96% had daily noise doses that exceeded the 

U.S. Mine Safety and Health Administration’s (MSHA) 

permissible exposure level. The average gold miner dosages while operating the following equipment were: haul 

trucks - 261%, load-haul-dumps (LHDs) - 235%, single 

boom drills - 221%, bolters - 214% and dual boom drills 

- 163%. The worst exposure level was a silver miner with 

a daily dose of 873%. Time-motion data showed that this 

miner’s exposure accumulated most rapidly while operating 

a jackleg drill. These results will be used to help prioritize 

noise control development by NIOSH and other partners. 

Introduction

Hearing loss and overexposure 

to noise continues to be a problem 

throughout the mining industry. 

Studies indicate that 70 to 90% of all 

miners have a noise-induced hearing loss (NIHL) severe enough to be 

classified as a hearing disability by 

the time they reach retirement age 

(Franks, 1996). To address this problem, as part of an 

ongoing strategic plan, the National Institute for Occupational Safety and Health (NIOSH) has been conducting 

a series of long-term noise surveillance and evaluation 

studies for the entire mining industry. Operator noise 

exposures were measured and tabulated for dissemination to the mine sites and analyzed to direct future noise 

control development. 

This report contains the description of studies conducted at U.S. western hardrock mines to determine the 

levels of miners’ noise exposure. Eighty-two noise dosimeter measurements were obtained from hardrock mining machine operators.Time-motion 

studies were performed as the operators used bolting machines, LHDs, 

haul trucks and drills. Of the operatiors, 96% had daily noise doses that 

exceeded the U.S. Mining Safety and 

Health Administration’s (MSHA) 

permissible exposure level (PEL). 

The only participants with exposures 

below the PEL were two bolter operators and one dual-boom drill operator. 

Approach to quantify noise exposure 

To evaluate the operators’ noise exposure, a sample 

population of each piece of equipment was monitored 

and the data analyzed using the following two research 

methods. 

1.	� Noise dosimetry was used to measure the machine operators’ total noise exposure during the 

course of their work day. 

2.	� Time-motion studies were used to identify work 

tasks and/or machines causing the higher doses 

that are in need of engineering noise controls or 

administrative controls. 

To complete these analyses, NIOSH researchers conducted noise surveys at eight underground metal mines 

located in the western U.S. to identify and quantify the 

noise exposure of hardrock underground machine operators. 

Noise dosimetry measurements 

The operators’ noise exposure was measured using 

a Quest Q-400 noise dosimeter. The dosimeter microphone was clipped to the midpoint of the operator’s 

shoulder with the diaphragm pointing up and worn for a 

full shift. The Quest Q-400 (Quest Technologies, 1997) is 

a single-microphone, dual-channel device that allows for 

independent user-configurable dose evaluation settings 

on each of the two channels.The two channels,referred to 

as dosimeter 1 and dosimeter 2, collect sound level measurements simultaneously. Dosimeter 1 was set according 

to the MSHA PEL (MSHA, 1999), and dosimeter 2 was 

set for wide-range data collection to measure and record 

all sound levels (Table 1).The MSHA PEL settings were 

used for consistency with the majority of noise dosim-
etry data reported for the U.S. mining industry. The 

wide-range data was collected for future analysis as 

part of a NIOSH equipment operators’ noise exposure 

database. 

Table 1 

Dosimeter settings. 

Dosimeter 

number 

Parameter Settings Designation 

Weighting	 A 

threshold level	 90 dB	 MSHA 

1	 exchange rate	 5dB	 permissible 

criterion level	 90 dB	 exposure 

response	 slow	 limit (PEL) 

upper limit	 140 dB 

Weighting	 A 

threshold level	 40 dB 

2	 exchange rate	 3 dB	 Wide range 

criterion level	 85 dB	 (Leq) 

response	 slow 

upper limit	 140 dB 

Time-motion study 

To determine when and where the miners were receiving most of their noise dose, time-motion studies were 

performed. Researchers recorded equipment position (at 

the face, in the drift), status (running (low idle, high idle), 

drilling, loading, tramming (moving) and the mining task 

duration. The internal clocks in the dosimeters and the 

clocks used by the time-motion study observers were 

time-synchronized so that exposures and observations 

could be directly associated in further analysis. The correlation of dosimeter and time-motion studies can be 

used to identify the machines, tasks, locations and other 

factors that are most responsible for a worker’s noise 

exposure. Once the factors are identified, appropriate 

risk reduction interventions can be selected and prioritized. The options include some combination of new or 

retrofit noise controls, improved maintenance of existing 

controls, adoption of administrative controls and use of 

hearing protection devices — only after all feasible engineering and administrative controls have been implemented. 

Gold mine findings 

The results of the gold mine dosimetry data are shown 

in Tables 2-6. These tables show the average work shift 

and time-weighted average full shift noise dose and 

equivalent TWA8 dB(A) - calculated to a standard eighthour shift, for operators of selected machines at the mine 

sites. The TWA8 dB(A) is used so that all work-shifts regardless of length can be easily compared. The standard 

deviation of the daily doses and the percentage of operators over the PEL are also shown in the tables. Figures 

1-5 are cumulative dose vs. time plot examples of one 

corresponding operator’s work shift, with some defined 

mining activities with selected dB(A) and dose levels. 

Note: the Y-axis scales vary between Figs. 1-5. 

Twenty-one bolter operators were fitted with dosimeters and time-motion studied; the results are summarized 

in Table 2. 

Table 2 

Bolter operators’ average work shift, TWA8 dB(A), and 

daily dose, range of doses, standard deviation of doses and 

percentage of overexposed operators.
�

Average duration 

of work (Hr:min) 

Average
�

TWA8 dB(A) Dose
�

11:23	 	 	 95	 Average: 214% 

Range of doses (N = 21)	 	 	 26% - 551% 

Standard deviation (Dose)	 	 	 130% 

Overexposed operators: 			90% 

Figure 1 is a cumulative dose plot of a representative bolter operator dose for the observation shift and 

pinpoints some of the major dose contributors. 

FIGURE 1 

Cumulative dose plot of a bolter operator’s work shift 

[08:10 to 18:20]. 

The operator’s daily dose for the observation shift was 289% 

or a TWA8 of 98 dB(A). The operator attained the permissible exposure limit of 100% dose at approximately 

1:30 p.m. (5.5 hours into his shift) and went on to almost 

triple his dose by the end of the shift. Time-motion studies show that the task with the highest noise exposure for 

the bolter operators was tramming, which contributed 

more than 74% of the cumulated dose on average (Durr, 

et al., 2005). 

Seventeen haul truck operators were fitted with dosimeters and time-motion studied. The results are summarized in Table 3. 

FIGURE 2 

Cumulative dose plot of a haul truck operator’s work 

shift [09:20 to 18:08]. 
Table 3 

Haul truck operators’ average work shift, TWA8 dB(A), and 

daily dose, range of doses, standard deviation of doses, and 

percentage of overexposed operators.
�

Average duration 

of work (Hr:min) 

Average
�

TWA8 dB(A) Dose
�

10:51	 	 	 97	 Average: 261% 

Range of doses (N = 17)	 	 	 114% - 575% 

Standard deviation (Dose)	 	 	 130% 

Overexposed operators: 		100% 

Figure 2 is a cumulative dose plot of a representative haul truck operator’s dose for the observation shift 

and pinpoints some of the major dose contributors. The 

operator’s dose for the observation shift was 455%, or 

a TWA8 of 101 dB(A). The operator attained the permissible exposure limit of 100% dose at approximately 

11 a.m., less than two hours into his shift. Time-motion 

studies show that the task with the highest noise exposure 

for the haul truck operators was tramming while loaded, 

which contributed more than 86% of the cumulated dose 

on average (Durr, et al., 2005). 

Fourteen LHD operators were fitted with dosimeters 

and time-motion studied. The results are summarized in 

Table 4. 

Table 4 

LHD operators’ average work shift, TWA8 dB(A), and daily dose, 

range of doses standard deviation of doses, and percentage of 

overexposed operators.
�

Average duration 

of work (Hr:min) 

Average
�

TWA dB(A) Dose
� 8

11:02	 	 	 96	 Average: 235% 

Range of doses (N = 14)	 	 	 111% - 438% 

Standard deviation (Dose)	 	 	 107% 

Overexposed operators: 		100% 

Figure 3 is a cumulative dose plot of a representative LHD operator’s dose for the observation shift and 

pinpoints some of the major dose contributors. 

FIGURE 3 

Cumulative dose plot of a LHD operator’s work shift [09:10 to 

18:18]. 

The operator’s dose for the observation shift was 167% or a 

TWA8of 94 dB(A).The operator attained the permissible 

exposure limit of 100% dose at approximately 3:30 p.m., 

about 6.5 hours into his shift.When the operator was able 

to turn the motor off between loading the haul trucks 

the cumulative dose was less than tramming or loading 

during the same time period. Time-motion studies show 

that the task with the highest noise exposure for the LHD 

operators was loading haul trucks, which contributed 

more than 67% of the cumulated dose on average (Durr 

et al., 2005). 

Nine single-boom drill operators were fitted with dosimeters and time-motion studied. The results are summarized in Table 5. 

Table 5 

Single-boom drill operators’ average work shift, TWA8 dB(A), 

and daily dose, range of doses, standard deviation of doses and 

percentage of overexposed operators.
�

Average duration 

of work (Hr:min) 

Average
�

TWA8 dB(A) Dose
�

12:23	 	 	 96	 Average: 221% 

Range of doses (N = 9)	 	 	 100% - 467% 

Standard deviation (Dose)	 	 	 120% 

Overexposed operators: 		100% 

Overexposed operators: 100 % 

Figure 4 is a cumulative dose plot of a representative 

single-boom drill operator’s dose for the observation shift 

and pinpoints some of the major dose contributors.

FIGURE 4 

Cumulative dose plot of a single-boom drill operator’s work 

shift [10:35 to 15:48]. 

Table 6 

Dual-boom drill average operators’ work shift, TWA8 dB, 

daily dose, range of doses, standard deviation of doses and 

percentage of overexposed operators.
�

Average duration 

of work (Hr:min) 

Average
�

TWA8 dB(A) Dose
�

10:23	 	 	 93	 Average: 165% 

Range of doses (N = 7)	 	 	 67% - 402% 

Standard deviation (dose)	 	 	 111% 

Overexposed operators: 		86% 

 The 

operator’s dose for the observation shift was 162%, or a 

TWA8 of 94 dB(A) in just over five hours of work. The 

operator attained the permissible exposure limit of 100% 
	 	 	

dose at approximately 2 p.m., after about three hours and 

25 minutes of work. Time-motion studies show that the 

task with the highest noise exposure was drilling with motor at high idle, which contributed more than 58% of the 

cumulated dose on average (Durr et al., 2005). 

Seven dual-boom drill operators were fitted with dosimeters and time-motion studied. The results are summarized in Table 6. 

Figure 5 is a cumulative dose plot of a representative 

dual-boom drill operator’s dose for the observation shift 

and pinpoints some of the major dose contributors.

FIGURE 5 

Cumulative dose plot of a dual-boom drill operator’s work shift 

[8:00 to 18:10]. 

 The 

operator’s dose for the observation shift was 167%, or a 

TWA8 of 94 dB(A).The operator attained the permissible 

exposure limit of 100% dose at approximately 2:30 p.m.. 

Time-motion studies show that the task with the highest 

noise exposure was drilling with motor at high idle, which 

contributed more than 89% of the cumulated dose on 

average (Durr, et al., 2005). 

Results of the gold mine studies showed that all 

but three of the 68 operators’ daily dose exceeded the 

MSHA’s PEL. The averaged daily noise dosages were as 

follows: 

1) 261% for haul truck operators, 

2) 235% for LHD operators, 

3) 221% for single-boom drill operators, 

4) 214% for bolter operators and 

5) 163% for dual-boom drill operators. 

Some of the high PELs are attributable to the studied workers having work shifts longer than eight hours. 

For example, a worker exposed to a constant 95 dB(A) 

during the shift will have a PEL of 200% (TWA8 of 95 

dB(A)) at eight hours and then a PEL of 250% (TWA8 

of 97 dB(A)) at 10 hours.The high standard deviation for 

the operator’s dose for a specific machine type can also 

be attributed to normal variations in the work process, 

including the following: 

• monitoring of different operators,
�

• operators’ degree of expertise,
�

•	� condition of the mine’s terrain (angled drift, 

heaved floor or debris on the floor), 

•	� presence of or the proximity of noisy equipment 

•	� quantity of work done, 

•	� turning off equipment vs. idling equipment when 

not in use and 

•	� exceeding vs. following the manufacturer-recommended drilling parameters for thrust,torque and 

rotational speed. 

Silver mine findings 

The workers selected for dose monitoring at the silver mine included miners, nippers, truck drivers and 

service mechanics. The noise dosimeters were worn for 

full 10-hour shifts. Since only 14 workers were studied at 

this silver mine and the number of workers in each job 

category was too small for computing reliable population statistics, the TWA8 dB(A) and daily dose for each 

individual are shown in one table. Table 7 summarizes 

the results of the dosimeter measurements.

Table 7 

Silver mine workers’ TWA8 dB(A) and daily dose. 

Occupation	 TWA8			

dB (A)
 

Dose
 

Miner 106 873%
�

Miner 105 829%
�

Miner 104 687%
�

Miner 102 552%
�

Miner 96 239%
�

Miner 96 218%
�

Nipper (helper) 101 431%
�

Nipper (helper) 93 154%
�

Nipper (helper) 91 115%
�

Truck driver 101 437%
�

Truck driver 100 428%
�

Truck driver 100 409%
�

Service mechanic 91 117%
�

Service mechanic 91 112%
�

These doses 

indicate that only one nipper (miner helper) and both 

service mechanics were below the citable MSHA dose 

of 132% (2 dB above the PEL’s TWA8 of 90 dB(A)). 

The remaining workers experienced doses significantly 

higher than the PEL (Bauer et al., 2001). 

FIGURE 6 

Cumulative dose plot of a silver miner’s work shift [5:45 to 

15:45]. 

Figures 6-9 

are cumulative dose vs. time plot examples of one corresponding operator’s work shift, with some defined 
mining activities with selected dB(A) and dose levels. 

Note: the Y-axis scales vary between Figs. 6-9. 

Miners 

A total of six miners wore a dosimeter for a full shift. 

One of the miners working in a ramp in one of the mine’s 

stopes was time-motion studied for a full shift. This was 

done to correlate dose with activities, tasks, locations and 

equipment. This miner was responsible for all aspects of 

stope/ramp development including: 

1) operating a jackleg drill to drill bolt holes and to 

install rock bolts, 

2) drilling the blast holes in the face with a dualboom drill (jumbo) and

 3)mucking the face with a loader. 

The miner also spent considerable time moving 

equipment and supplies around the face area. During 

the observation shift, the miner used the jackleg drill to 

support the rib and roof with chain link fencing, operated 

the dual-boom drill and loaded explosives in the blast 

holes in preparation for shooting the face.The miner only 

operated the loader to move supplies and assist in installing the chain link fencing to support the roof and ribs. 

Figure 6 is a cumulative dose plot of the miner’s dose 

for the observation shift and pinpoints some of the major 

dose contributors. The total dose for the observation shift 

was 829%, or a TWA8 of 105 dB(A). The miner attained 

100% dose approximately two hours after the start of the 

shift and 132% (MSHA citable dose) approximately 15 

minutes later.The major contributor to the total dose was 

operation of the jackleg drill to drill bolt holes and the 

installation of rock bolts to hold the chain link fencing for 

rib and roof control. 

Nipper 

Three nippers, or miner helpers, were monitored, with 

one being time-motion studied for approximately half a 

shift.The nipper’s main tasks are to assist the miners.This 

includes operation of all stope equipment, especially the 

loader and supply tractor. During the observation period, 

the nipper was building a muck wall in one mine stope. 

The nipper accomplished this task by moving muck from 

the muck bay near a ramp in another location and hauling it down into the stope with a 1.8-m (6-ft) loader. As 

illustrated in Fig. 7, the nipper received approximately 

95% of the total dose during the 140 minutes of loader 

operation. 

FIGURE 7 

Cumulative dose plot of a nipper’s work shift [5:55 to 15:55]. 

Service mechanic 

The service mechanic was monitored for just two 

shifts, but was observed for most of one of the shifts. The 

work tasks included driving the service car to each of the 

stopes and servicing (greasing and adding diesel fuel and 

hydraulic oil) the dual-boom drills (jumbos) and loaders. 

The time spent servicing each piece of equipment varied, 

and during the observation shift ranged from a low of 

six minutes to a high of eighteen minutes. The average 

service time was approximately twelve minutes, which 

in many cases, occurred in the vicinity of an overhead 

auxiliary fan. Figure 8 is the cumulative dose plot for the 

service mechanic’s dose during the shift he was observed. 

FIGURE 8 

Cumulative dose plot of a service mechanic’s work shift [5:45 

to 15:45]. 

The daily dose of 117% and a TWA8 of 91 dB(A) were 

below the citable MSHA dose, but still above the PEL. 

The major contributors of the total dose, as indicated on 

Fig. 7, were the noise generated by the service tractor 

while tramming from one stope to another and servicing 

equipment near the auxiliary fans. 

Truck drivers 

The truck drivers operated single-seat, open-cab 

muck trucks running from the muck piles to the grizzly and could not be safely time-motion studied by the 

researchers. However, the daily doses were highly consistent among the three, ranging from 409 to 437 percent, 

and a TWA8 range of 100 to 101 dB(A) was measured 

for all three drivers. This high degree of consistency and 

the repetitive, continuous nature of the task support a 

conclusion that the noise was primarily from operating 

the truck. From the gold mine time-motion studies, the 

highest noise exposure rates occurred while performing 

the task of “tramming while loaded,” which contributed 

more than 86% of the cumulated dose on average (Durr 

et al., 2005). Figure 9 is the cumulative dose plot for a 

haul truck operator’s work shift in a silver mine. The operator attained the permissible exposure limit of 100% 
dose at approximately 8:20 a.m., less than three hours 

into the work shift. The daily dose for this operator was 

409% and a TWA8 of 100 dB(A). 

FIGURE 9 

Cumulative dose plot of a haul truck operator’s work shift [5:45 

to 15:45]. 

Summary and discussion 

This study found high levels of hazardous noise 

exposure to be common at the sampled U.S. western 

hardrock mines, where noise generated by some of the 

larger hardrock mining equipment was measured to be 

in excess of 113 dB(A). While the data can be used as 

a comparative reference, each operation is encouraged 

to perform a site-specific noise survey to determine its 

workers’ noise exposure as a basis for a local hearing 

loss prevention program. If an individual daily noise 

dose is unusually high, that operator or job position 

should be observed to identify the causes and select 

appropriate exposure reduction interventions. 

To address the hazardous noise exposures, appropriate interventions should be matched to the noise 

sources and tasks. While some pieces of equipment can 

be retrofitted with noise controls, other methods such 

as administrative noise controls and hazard awareness 

training can be used to reduce the miners’ exposure to 

noise. One example from the current study illustrates 

this point: While a service mechanic was observed 

repairing equipment next to a loud auxiliary fan, he 

rapidly accumulated an elevated noise dose (shown 

by a steep slope in the plot in Fig. 8). However, when 

he moved away from the fan to service equipment in 

another location, his exposure dropped considerably, 

shown by a relatively flat segment on the cumulative 

dose line. For situations like this, miners should be made 

aware that noise exposure is cumulative throughout the 

day, and making an effort to move equipment to a quieter working area will reduce the potential for NIHL. 

Additional guidance on technologically and administratively achievable engineering and administrative 

noise controls is available from MSHA’s Program Information Bulletin P08-12 (PIB) (MSHA, 2008). This PIB 

presents technologically or administratively achievable controls that individually or in combination have 

been shown to achieve at least a 3 dB(A) reduction in a 

miner’s noise exposure. Some of the engineering noise 

controls MSHA considers to be technologically achievable in reducing the noise exposure of miners operating 

mobile equipment include the following: 

•	� Acoustically treated environmental cabs. 

•	� Barriers,such as windshields and partial acoustic 

panels. 

•	� Exhaust mufflers. 

•	� Redirection of the exhaust away from the operator. 

The PIB considers the following to be applicable examples of administrative controls: 

•	� Sharing of work tasks and/or rotation of miners 

from noisy activities to quieter ones. 

•	� Limited duration of work shifts. 

•	� Providing quiet areas while taking breaks. 

•	� Eliminating tasks that are unnecessarily noisy. 

•	� Restricted or limited miner access to high noise 

areas. 

•	� Following of manufacturer-recommended drilling parameters for thrust, torque and rotational 

speed. 

Hearing loss and overexposure to noise continues to 

be a problem throughout the mining industry.This study 

shows some of the work tasks and machinery that cause 

overexposure to hardrock miners. Using information 

about exposures and with a variety of suitable noise 

controls to choose from, it becomes much more feasible 

to reduce noise exposure and the risk of NIHL. 

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. 

References 

Franks, J.R., (1996), “Analysis of audiograms for a large cohort of 

noise-exposed miners,” U.S. Department of Health and Human 

Services, Public Health Service, Centers for Disease Control and 

Prevention, National Institute for Occupational Safety and Health, 

Division of Biomedical and Behavioral Science Cincinnati, OH 

(Unpublished). 

Instructions for Q-400 and Q-500, (1997), Quest Technologies 56-253, 

Rev. F. 

MSHA, (1999), “Health Standards for Occupational Noise Exposure; Final Rule,” Department of Labor, Mine Safety and Health 

Administration, Federal Register 30 CFR Parts 56 and 57, et al., 

64(176):49548-49634. 

Durr,T.M. and E.R. Reeves,(2005),“NIOSH Nevada Gold Mine Noise 

Survey Summary,” Slide presentation at the Western Underground 

Mining Association Conference in Elko, NV, June 9, 2005. 

Bauer, E.R., M.D. DiMartino, P.J. Hintz, E.R. Spencer and Vipperman, 

J., (2001), “Investigation of Noise Sources at an Underground 

Silver/Lead/Zinc Mine,.” Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, 

Hearing Loss Prevention Branch. Unpublished. 

MSHA, (2008),“Technologically Achievable,Administratively Achievable, and Promising Noise Controls,” Department of Labor, Mine 

Safety and Health Administration, Program Information Bulletin 

P08-12 (30 CFR Part 62), http://www.msha.gov/ regs/complian/ 

pib/2008/pib08-12.pdf.