Noise Exposure and Hearing Conservation in US. Coal 

Mines-A Surveillance Report 

Gerald J. Joy1 and Paul J. Middendorf2 

lCDC/NIOSH/Pittsburgh Research Laboratory, Pittsburgh, Pennsylvania 

2CDC/NIOSH/Office of the Director, Cincinnati, Ohio 

This study examines the patterns and trends in noise 

exposure documented in data collected by Mine Safety arzd 

Health Adnzinistmtion inspectors at U.S. coal mines from 

1987 through 2004. During this period, MSHA issued a 

new regulation on occupational noise exposure that changed 

the regulatory requirements and enforcement policies. The 

data were examined to identify potential inzpacts from these 

changes. The overall annual median noise dose declined 

67% for sur$ace coal mining and 24% for underground coal 

mining, arzd the reduction in each group accelerated after 

promulgation of the new noise rule. Howevel; not all mining 

occupations experienced a decrease. The exposure reduction 

was accompanied by an increase of shift length as represented 

by dosimeter sample duration. For coal miners exposed above 

the permissible exposure level, use of hearing protection 

devices increased from 61% to 89% during this period. 

Participation of rniners exposed at or above the action level in 

lzearing conservation programs rapidly reached 86% following 

the eflective date of the noise rule. Based on inspection data, 

the occupational noise regulation appears to be having a strong 

positive i~npact on hearing conservation by reducing exposures 

and increasing the use of lzearing protection devices and 

medical surveillance. Howevel; the increase in shift duration 

and resulting reduction in recovery time may mitigate the gains 

somewhat. 

Address correspondence to: Gerald Joy, NIOSH-RHCB, P.O. Box 

18070, Pittsburgh, PA 15236-0070; e-mail: gej3 @cdc.gov. 

The findings and conclusions in this report are those of the authors 

and do not necessarily represent the views of the National Institute 

for Occupational Safety and Health. 

INTRODUCTION 

M ining of in situ minerals requires highly energetic 

extraction methods, exposing miners to high noise 

levels. In 1981, the United States Environmental Protection 

Agency (EPA) estimated that 255,000 miners were exposed to 

daily noise levels above 85 decibels on the A-weighted scale 

(~BA).(') This represented about 47% of miners, including 

employees and contractors. In a subsequent assessment(2) performed from 1984 to 1989 by the National Institute for Occupational Safety and Health (NIOSH), the National Occupational 

Health Survey of Mining (NOHSM) estimated that 108,264 

(87.8%) of miners in the bituminous coal and lignite Standard 

Industrial Classification code were occupationally exposed 

to noise. Both of these estimates demonstrated widespread 

exposure to elevated noise levels and the associated increased 

risk of developing noise-induced hearing loss (NIHL) in the 

mining industry. However, these estimates may not accurately 

represent the current coal mining work force, which from 

1987 to 2004 has decreased by 57% for coal, excluding office 

workers.(3) In addition, mining technologies have changed and 

noise reduction controls have become available. 

The purpose of this report is to describe patterns of noise 

exposure in the coal mining sector using compliance samples 

collected by Mine Safety and Health Administration (MSHA) 

inspectors. A secondary objective is to provide a baseline for 

future review of the impact of the MSHA Occupational Noise 

Exposure regulation on noise exposures in coal mining. 

Federal Regulation of Occupational Noise Exposure 

in Mining 

Before 2000, MSHA enforced a permissible exposure level 

(PEL) for noise exposure in coal mining that was derived 

from the Walsh-Healy Public Contracts Act. The PEL was 

an 8-hour, time-weighted average (TWAs) of 90 dBA, and 

unless a citation was issued for overexposure to noise, hearing 

conservation programs were not mandated. The prior MSHA 

noise regulations did not specify engineering and administrative controls as the primary methods to reduce coal miners' 

noise exposures. 

MSHA internally reviewed the effectiveness of its noise 

standard and determined that the risk of developing NIHL 

from exposures at or above the PEL was unacceptably high, 

and some residual risk of NIHL remained for miners exposed 

below the PEL.(^) MSHA analyzed the impact of alternative 

compliance strategies to reduce the NIHL risk to miners including reducing the PEL to a TWAs of dBA, and the doubling 

rate from 5 dB to 3 dB for noise exposure measurements. 
MSHA determined that reducing the PEL to 85 dBA would 

require 75% of coal mine operators to install engineering 

controls or use administrative controls while changing the doubling rate to 3 dB would double the percentage of noncompliant 

measurements. MSHA thus concluded that these changes were 

not technologically or economically feasible for the mining 

industry.(5) 

As a result of its review, MSHA issued a final occupational 

noise exposure rule codified at 30 CFR 62 in 1999 that became 

effective in September 2000 and included several significant 

changes: 

1. The compliance requirements for the metal and nonmetal mining sector (not included here) and coal were 

made the same. 

2. Primacy of engineering and administrative noise controls in both sectors was established. 

3. Mine operators were required to implement a monitoring 

system to evaluate the noise exposures of miners. 

4. A TWA8 action level (AL) of 85 dBA (a dose of 50%) 

was established. 

5. Enrollment in a hearing conservation program was 

required for miners exposed at or above the AL, and , 

6. A statutory definition for hearing loss cases that must 

be reported to MSHA based on audiometric testing was 

established (a deterioration in hearing sensitivity of 25 

dB or more at 2000, 3000 and 4000 Hz in either ear, 

relative to the appropriate baseline audiogram). 

The MSHA noise regulation specifies that the PEL measurement includes all sound pressure levels (SPLs) from 90 dBA 

to at least 140 dBA, whereas the AL measurement includes all 

SPLs from 80 dBA to at least 130 ~BA.(') Both measurements 

use a 5-dB doubling rate, a reference time of 8 hours, a 

reference SL of 90 dBA, and slow response. 

METHODS 

C ompliance samples collected using personal noise 

dosimeters were downloaded from MSHA's inspection 

database from 1986 (the start date of the database) through 

2004. Dosimetry results are reported in dose percent. 

MSHA maintains two data repositories for coal sector noise 

exposure samples. One repository contains records for the period from 1986 through 1999 and is maintained by the MSHA 

Safety and Health Technology Center in Bruceton, Pennsylvania; the other is the active MSHA management information 

system, and it contains noise exposure records from 2000 

onward. Noise exposure-related data were extracted from both 

repositories. No information that would permit personal identification of either MSHA inspectors or mine employees was 

retrieved. 

The two data sets were formatted into separate data files 

using SPSS 12.0 for Windows. The two data files had 

differing structures because MSHA's inspection and data 

collection practices changed in response to the September 

1999 promulgation of the occupational noise exposure regulation. However, the key variables used for this analysis 

(i.e., exposure dose percent, occupation, sample date, and 

sample duration) were present in both datasets. These ley 

variables were assigned identical names and formats, whereas 

all other variables were retained and the two data files were 

merged. 

The combined file included 148,8 13 noise exposure records. 

The data were edited to exclude potentially invalid samples 

prior to the analysis. Records were excluded if any of the 

following criteria were met: 

II There were duplicate cases. 

II No value for survey date was given, or the survey date was 

before January 1, 1987, or after December 3 1,2004. 

II No value for the PEL dose was given. 

II The PEL dose exceeded the AL dose (where dual-channel 

dosimeters were used to simultaneously measure PEL and 

AL doses). 

The occupation was invalid or missing. 

No sample time was recorded, or the sample time was less 

than 6 hours or greater than 16 hours. 

A small number (22) of records had extremely high PEL 

doses (e.g., 9999%). These doses were considered transcription 

errors and were excluded. Similarly, sample durations of less 

than 6 hours (0.8% of all records) and greater than 16 hours 

(0.03% of all records) were considered nonrepresentative and 

were also excluded. 

Based on the above criteria, 6,281 records (4.2%) were 

excluded, resulting in 142,735 exposure records that were used 

for analysis. 

MSHA's Coal Mine Health Inspection Procedures Handbook specifies the procedures to be followed during a noise 

compliance inspection.(') American National Standards Institute (ANSI) Type I1 noise dosimeters are used to collect 

personal noise exposure measurements. Dosimeter parameters (threshold level, criterion level, doubling rate, etc.) are 

specified for action level and permissible exposure level 

measurements, and dosimeters and calibrators are laboratory 

calibrated annually to assure conformity to ANSI standards 

for Type I1 instruments. MSHA inspectors perform pre- and 

postsampling field calibration checks on the dosimeters. If a 

dosimeter is not within f 1.0 dB of the calibration value, the 

dosimeter or the collected exposure data is not used and is not 

included in the database. 

Shift length is not specifically recorded in the MSHA 

databases; however, sample duration is used in this analysis 

as a surrogate measure of shift length because MSHA's policy 

is to collect full-shift "portal-to-portal" noise samples. 

The noise exposure databases include both a measured noise 

dose and, for samples collected prior to 2000, an adjusted noise 

dose when hearing protection devices (HPDs) were worn by the 

monitored miners. This allows an examination of the patterns 

of HPDs use. In the pre-rule period (before 2000), information 
1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 

FIGURE 1. Coal mine noise sampling and employment trends 1987-2004 

about the use of HPDs among coal miners was collected 

to adjust the measured noise dose based on the protection 

provided by the HPD, in accordance with the prevailing coal 

mine health inspection procedures. No information about the 

type of HPD used was documented. For this analysis, where 

the pre-rule exposure record contains a value for adjusted dose 

that is less than the measured dose, it is assumed that the 

miner wore hearing protection during the sampling event. Only 

unadjusted (measured) noise dose values are ~zsed to represent 

miner exposure in this analysis. 

The data sets were examined for normality. The Lilliefors 

Komolgorov-Smirnov test rejected normality for the PEL and 

AL noise dose data (p < .001), and the natural log transform 

of the PEL and AL dose data (p < .001). 

The post-rule (after 1999) data contain a small number 

of extreme values of dose (>2000%); rendering means an 

inappropriate statistic to represent the data. Consideration was 

given to censoring the extreme values prior to analysis, but 

this approach was not supported by any available information. 

Consequently, medians of dose are used to characterize central 

tendency, and the interquartile range is used to represent the 

spread in the data. 

The trends in exposure were determined using linear 

regression of the annual median PEL dose on calendar year for 

the pre-rule (1987-1998) and post-rule (2000-2004) periods. 

Calendar year 1999 is excluded from the analysis because the 

final rule took effect during the year, causing differing criteria 

to apply in parts of the year. For the AL, only the period 

from 2000 through 2004 was analyzed. Linear regressions 

were performed using SAS v. 9.1; figures were generated with 

Sigmaplot 2004 for Windows v. 9.01. 

RESULTS 

a he average annual number of PEL noise samples recorded 

increased during the years after the occupational noise 

exposure regulation was issued in 1999. The average annual 

number of workers' exposures recorded in the 4-year period 

from 1995 to 1998 was 6098. The average annual number 

for the 2000 through 2004 period was 8839, a 45% increase. 

The number of exposure records in 1999 was unusually low 

because very few were recorded in September and October of 

that year; for this reason, 1999 is not included in the sample 

count comparison. 

Annual noise sample counts and employment totals are presented in Figure 1. Vertical reference lines have been overlaid 

on each figure to represent the occurrence of significant events 

in the development of the noise regulation. The definitions 

of these reference lines are: ANPRM-advance notice of 

proposed rulemaking (1 210411 989); Proposed-publication 

of the proposed noise regulation (1211 7/1996), PubDatepublication date of the final noise regulation (0911311999); 

and EflDate-effective date of the final noise regulation 

(0911 312000). 

The number of operating coal mines and the fraction of 

operating mines surveyed by year is presented in Figure 2. The 

number of mines inspected for noise exposures per year generally declined from 1987 to 1999. Based on MSHA's published 

data,(7) the fraction of operating coal mines inspected remained 

relatively constant before the final rule but has increased since 

the final occupational noise exposure rule has been in effect. 

The increase in sampling activity matched a reduction in the 

annual median PEL dose from 62.2% in 1998 to 34% in 2004 
(1999 is excluded beca~lse the final rule took effect within included in Table I to provide additional description of the 

that calendar year). Reductions are seen in both the annual data. The means of the underground and surface occupation 

median PEL dose for noise samples talcen on underground doses for the 1987-1989 and the 2000-2004 periods were 

occupations (74% to 50%) and surface occupations (48.8% significantly diflerent by the Mann-Whitney U test (p < 0.001 

to 20%) (Table I). Annual means and standard deviations are for both). 

TABLE I. PEL Dose Sample Descriptive Statistics by Year and Location 

Surface Underground 

PEL Dose Percent PEL Dose Percent 

Year N Mean SD Median IQ Range N Mean SD Median IQ Range 
@ UG PEL 87-98 v SF PEL 00-04 

s-va UG PEL 87-98 Reg. - SF PEL 00-04 Reg. 

UGPELOO-04 61s UGAL 

-m - UG PEL 00-04 Reg. em**D UG AL Reg. 

+ SF PEL 87-98 * SFAL 

- SF PEL 87-98 Reg. . . . . . . . SF AL Reg. 

Converting the median PEL doses to A-weighted sound 

levels using Eq. 1 

the reductions in dose represent a decrease in TWA8 exposure 

from 87.1 dBA to 82.2 dBA for all samples; from 88.2 dBA 

to 85 dBA for underground samples, and from 86 dBA to 

78.4 dBA for surface samples. The median noise doses in 

underground and surface occupations and the trends in median 

doses are presented in Figure 3. 

In underground occupations the median PEL noise dose 

increased at the rate of 0.84% per year from 1987 through 

1998 (pre-rule). For the post-rule period from 2000 through 

2004, the median PEL noise dose declined at the rate of 2.8% 

per year. The increase in pre-rule doses appears to be consistent 

through when the new rule was adopted in 1999. The median 

AL noise dose in underground occupations decreased at an 

identical rate of 2.8% per year. 

In surface occupations the median PEL noise dose decreased at the rate of 0.40% per year during the pre-rule period. 

The rate of decline increased in the post-rule period to 2.5% 

per year. The median AL noise dose in surface occupations 

decreased at the rate of 3.4% per year. 

The median PEL doses in surface and underground in 

1987 were of similar magnitude; however, by 1998 the 

PEL doses were substantially different. During the post-rule 

period, the median underground PEL noise doses also dropped 

substantially but not as much as the drop in surface PEL noise 

doses during the same period. The rate of change is similar 

for both underground and surface, but the PEL noise doses are 

substantially less in surface occupations than in underground 

occupations. The trends in surface and underground median 

AL noise doses during the post-rule period are similar to 

the trends and differences noted in the median PEL noise 

doses. 

Occupation Data 

MSHA lists 201 occupations that are used to describe the 

primary activity performed by a miner during a sampling 

event.(') The list of occupations has been relatively stable over 

the period examined by this report; a few new occupations were 

added when new production technologies were introduced. The 

number of noise samples collected in each occupation varied 

widely; no samples were collected in nine occupations. For 
sampled occupations, the number of samples per occupation 

ranged from one (nine occupations) to 15,942 (high lift 

operatorlfront end loader operator). The median number of 

samples per occupation was 7 1.5; the mean number of samples 

was 743.4. Not all occupations were sampled each year, and 

the number of samples per year in any occupation was variable. 

Underground Occupations 

Twenty-five underground occupations were represented by 

at least 100 samples in both the pre- and post-rule periods. 

Of these occupations, the median PEL dose in the 2000- 

2004 period was lower than in the 1987-1998 period in 18 

occupations (72%) and was unchanged in one occupation (4%). 

The median PEL dose increased from the 1987-1998 period 

to the 2000-2004 period in six occupations (24%) (Table 11). 

The occupations that displayed an increase between the two 

periods were headgate operator, jack setter (longwall), longwall operator (headgate side), longwall operator (tailgate side), 

roofbolter (mounted-intake side), and roofbolter (mountedreturn side). 

Sun'ace Occupations 

Twenty-nine surface occupations had at least 100 samples 

in both the pre- and post-rule periods. For 28 of these 29 

occupations (97%), the median PEL dose in the 2000-04 

period was less than in the 1987-1998 period. The remaining 

occupation was unchanged (Table 11). 

Hearing Conservation Programs 

In association with the new noise rule, MSHA inspectors 

began collecting information during inspections to document 

enrollment of the monitored miners in hearing conservation 

programs (HCPs). HCP-enrollment percentages of monitored 

miners by AL noise dose are presented in Table 111. Note that 

miners with noise dose equal to or greater than the AL were 

not required to be enrolled in an HCP until the fourth calendar 

quarter of 2000. 

Use of Personal Protective Equipment (PPE) 

Approximately 36% (35,603 samples) of pre-rule PEL 

samples included a reduced adjusted dose, suggesting that only 

36% of monitored miners wore HPDs. Of the 36% of miners 

who wore HPDs less than half (43%) were exposed to noise in 

excess of the PEL. 

During inspections in the post-rule period, MSHA inspectors document the use of HPDs, and specify which of three 

generic types (cap, muff, or plug) is used by the monitored 

miner. The descriptions of the types of HPD are: caps occlude 

the outer opening of the ear canal, muffs cover the entire pinna, 

and plugs are inserted into the ear canal. Some records indicate 

that the miner used more than one type in combination (e.g., 

muff and plug). 

The percentage of miners monitored during an inspection 

in a year and that used any type of HPD was categorized by 

the PEL noise dose range and presented in Figure 4. 

HPD use increased during the period reviewed for sampled 

miners in all noise dose ranges, although the increase is small 

for the two highest dose ranges (150% to 199%, and greater 

than 199%) because HPD use is high throughout the entire 

period. 

Most monitored miners exposed to noise used hearing 

protection-predominantly the plug type, although 13% of 

underground miners and 9% of surface miners exposed to 

greater than 100% PEL noise dose did not use HPDs in 2004. 

Surface miners were more likely to use HPDs than were 

underground miners. 

In the 5 years for which data are available, plugs are used by 

a large majority (89%) of monitored ininers who used HPDs. 

Muffs are the second most common choice (lo%), and cap 

type are used by only 1 % of miners who used HPDs. 

DISCUSSION 

M SHA coal mine inspection policies and methods have 

been relatively constant since the 1980s, permitting 

comparison of data collected over a long period at locations 

throughout the United States. MSHA's policy is to conduct 

annual noise compliance inspections at each producing mine, 

with follow-up surveys conducted where PEL dosimetry 

measurements are between 100% and 132%. 

Where PEL dosimetry exceeds 132%, an initial follow-up 

survey is to be conducted after implementation of feasible 

engineering and administrative controls. A subsequent followup survey is to be conducted within 60 days of the initial followup survey to assess continuing compliance. The relatively 

consistent policies and methods over this extended period, as 

well as the requirements to record all exposures collected, make 

the database a valuable tool for surveillance of noise exposures 

in the mining industry. However, there is some variability in 

the procedures that must be accounted for to interpret the data 

appropriately. For example, MSHA inspectors are responsible 

for assessing whether mining operations are in compliance 

with MSHA regulations; to assess compliance they identify 

and sample miners with the highest potential noise exposure 

(worst case). Generally, at least five individuals are sampled 

during a noise survey, although the selection of occupations 

to sample is based on procedures in the Coal Mivze Healtlz 

Ivzspectiorz Hnrzdbook that specify that the exposures of miner 

operators, roof bolters, shuttle car operators, and mobile bridge 

conveyor operators in underground mines will be sampled. In 

surface mines, bulldozer operators and other heavy equipment 

operators must be sampled when present in the workplace. The 

MSHA inspectors may select other occupations exposed to 

high levels of noise. These MSHA policies result in variability 

in the number of noise samples collected from the various 

occupation codes. 

The number of samples collected per year increased after 

1999. This increase in samples collected can be attributed to 

several factors. MSHA has performance objectives related to 

reduction of health hazards, including noise exposure, defined 

within its strategic plan developed pursuant to the Government 
TABLE II. Median PEL Doses of Coal Mining Occupations Sampled at Least 100 Times 

1987-1998 2000-2004 

Occupation Code and Description N Median N Median 

Underground Occupations 

001 Belt manlconveyor man 27 1 44.0 110 32.0 

002 Electrician 178 31.7 225 25.0 

004 Mechanic 454 36.0 236 24.0 

012 Roof bolter (twin head) (intake side) 2479 7 1.3 1548 59.0 

014 Roof bolter (twin head) (return side) 23 19 70.3 1617 59.0 

019 Roof bolter (mounted) (intake side) 3 10 94.7 104 126.5 

034 Coal drill operator 1235 52.4 183 25 .O 

035 Continuous miner helper 2324 79.0 337 72.0 

036 Continuous miner operator 8866 93.0 3617 93.0 

038 Cutting machine operator 1113 77.0 147 43.0 

040 Headgate operator 425 98.0 184 101.5 

041 Jack setter (longwall) 596 77.0 242 81.0 

043 Loading machine operator 606 98.5 100 94.5 

044 Longwall operator (tailgate side) 374 121.1 173 151.0 

046 Roof bolter (single head) 7146 69.0 1461 53.0 

048 Roof bolter (mounted) (return side) 427 93.7 156 109.0 

049 Section foreman 353 46.7 244 32.5 

050 Shuttle car operator (standard side) 6490 53.0 3388 44.0 

053 Utility man 498 40.1 276 38.0 

054 Scoop car operator 3413 41.6 1671 27.0 

064 Longwall operator (headgate side) 273 120.8 140 128.0 

072 Mobile bridge operator 1477 74.0 708 56.0 

073 Shuttle car operator (off standard) 2557 49.3 752 38.0 

074 Tractor operator/motoman 495 55.9 234 46.0 

101 Belt manlconveyor man 297 37.0 260 27.0 

Surface Occupations 

302 Electrician 45 8 38.6 3 17 28.0 

304 Mechanic 1970 25.7 980 18.0 

307 Blaster/shooter/shotfirer 139 27.5 111 23 .O 

3 10 Scrapper operator 880 79.3 163 43.0 

3 13 Cleanup man 370 80.2 156 64.5 

3 16 Laborer/blacksmith 1598 45.0 736 27.0 

3 18 Oilerlgreaser 837 92.0 328 53.0 

3 1 9 Welder (shop) 297 27.0 100 24.0 

324 Backhoe operator 654 33.7 704 9.0 

328 Utility man 797 38.7 868 19.0 

34 1 Belt man/conveyor man 254 49.5 131 31.0 

343 Car trirnrnerlcar loader 297 16.0 121 16.0 

345 Crusher attendant 290 59.5 152 28.0 

357 Washer operator 308 82.0 128 36.5 

368 Bulldozer operator 8869 92.1 5 198 41.0 

370 Auger operator 557 176.0 338 7 1 .O 

37 1 Auger helper 45 8 160.4 254 76.0 

374 Cleaning plant operator 1126 64.0 707 37.0 

375 Road grader operator 572 39.1 345 21.0 

376 Coal truck driver 938 42.0 474 15.0 

378 Crane operatorldragline operator 883 27.0 390 7.5 

380 Fine coal plant operator 569 95.4 335 68.0 

382 Highlift operatorlfront end loader 10,207 51.3 5193 16.0 

384 Highwall drill operator 2416 70.5 1181 19.0 

386 Refuse truck driverlbackfill truck driver 4343 49.0 2746 18.0 

387 Rotary bucket excavator operator 133 38.7 185 8.0 

39 1 Stripping shovel operator 273 30.0 185 6.0 

392 Tipple operator 1767 48.0 507 20.0 

393 Weighman 233 8.0 112 2.5 
TABLE III. Coal Miner Hearing Conservation Program Enrollment 

Enrollment in HCP 

Action Level 

Dose Range 2000 2001 2002 2003 2004 

(%) (1 (%I (%) (%) (%I 

0-49 9 6 8 76 76 77 

50-99 7 74 84 85 8 5 

100-149 7 8 1 91 8 9 88 

150-199 3 77 90 9 1 89 

> 199 5 70 87 8 5 82 

Subtotal 250 6 76 87 8 6 86 

Total 7 7 3 8 2 82 82 

Performance and Results Act of 1993. MSHA's strategic plan 

in part drives how its compliance activities will be directed, and 

the increase in noise sample collection is partially a result of 

this planning. In addition, after the publication of the new noise 

rule and before it became effective, MSHA delivered substantial technical support to the coal mining industry to assist with 

identification of noise sources that resulted in exposures greater 

than the AL andlor PEL. Some of this assistance took the form 

of additional targeted sampling to evaluate noise exposures and 

identify sources. A third possible contributing reason may be 

the evaluation of additional exposure situations for compliance 

with the new action level. 

Before 2000, the median PEL noise doses were increasing 

slowly for underground miners and decreasing slowly for 

surface miners. The increase in the median PEL dose for underground miners reversed and the decrease in noise exposures for 

surface miners accelerated when the MSHA final occupational 

noise exposure rule became effective, suggesting that the noise 

rule may have catalyzed actions that resulted in a reduction in 

miners' noise exposures. 

The reduction in median noise dose can be attributed to 

several factors. One factor is actions taken by coal mine 

operators motivated by the new rule's requirements specifying 

administrative and engineering controls as the primary means 

to reduce noise exposure. Examples of actions operators may 

have taken include retiring old, noisy equipment; retrofitting 

equipment with noise controls; and implementing administrative controls to reduce exposure. Whereas the period between 

the publication of the rule and its effective date is 1 year, 

the history of the noise rule legislation is considerably longer 

(Figure 3). MSHA published an Advance Notice of Proposed 

Rulemaling (ANPRM) for the noise rule in December 1989 

and issued a proposed noise rule in December 1996. The 

final rule was published in September 1999 with an effective 

date of September 2000. This multiyear period gave coal 

mine operators adequate notice of the likely changes to be 

implemented and permitted deliberate introduction of feasible engineering and administrative controls to reduce noise 

exposure. 

Another potential contributor to the observed decreases 

in PEL noise dose is the compliance assistance sampling 

performed by MSHA inspectors between September 1999 

and September 2000. If compliance assistance samples were 

collected during this period on a variety of processes and 

0 - 49% Dose ................... 49 - 99% Dose ------ 99 - 149% Dose -..-..-..- 149 - 199% Dose 
occupations that previously were not sampled because they 

were anticipated to have exposures below the PEL and the 

exposures were lower, the annual median for 1999 and 2000 

would have been reduced. This pattern is not observed for 1999 

but appears to contribute to the substantial drop in median PEL 

noise dose in 2000-2004. 

The seemingly permanent drop in noise PEL dose in 

2000-2004 may have been caused at least in part by the 

inclusion of processes and occupations that were sampled 

during 2000-2004 because exposures are anticipated to be at 

or above the AL but were not sampled previously because their 

exposures were below the PEL. Therefore, the observed noise 

exposure reduction since the new rule was adopted may not be 

exclusively a result of an overall reduction in noise exposures. 

However, the slopes of the regression lines suggest that some 

reductions in noise exposure are occurring. The reduction in 

overall noise exposure shown by the MSHA data may, if it 

continues, result in reduced incidence of NIHL among coal 

miners. 

A potential factor impeding the reduction of NIHL risk is 

an increase in miners' exposure time. The annual mean sample 

duration of coal miners increased from 8.22 hours in 1987 to 

9.35 hours in 2004, a 13.8% increase. For the miners in occupations with decreased noise dose but increased shift length, 

the increase in shift length may partially or wholly offset the 

benefit from the declining annual median noise exposure if 

the "equal energy equal hearing loss" hypothesis that the same 

amount of energy produces the same hearing loss is pertinent. 

The increased shift length is particularly concerning because it 

may result in greater temporary threshold shift (TTS)(') during 

the work shift among miners who may not be able to return to 

baseline hearing ability by the time work is begun again and the 

noise exposure resumes. Under the theory that a greater TTS 

results in greater permanent hearing loss,(lO) the increased shift 

length may result in increased rates of permanent NIHL. For 

miners in occupations with increased noise dose and increased 

shift length, an increase in NIHL incidence can be anticipated 

unless they are included in an effective hearing conservation 

program. 

An important aspect of the hearing conservation program 

specified by the final noise rule is the establishment of a standard definition for hearing loss that must be reported to MSHA 

by the mine operator. Formerly, hearing loss was reported 

when a miner was awarded compensation for NIHL through 

a workers' compensation system, or was diagnosed with a 

hearing loss. Differing standards used by the various statebased compensation agencies and inconsistent definitions used 

by medical professionals caused confusion for mine operators 

regarding which cases of hearing loss should be reported. The 

inconsistent definitions also reduced the usefulness of the data 

that were reported to characterize the extent and severity of 

NIHL in the mining industry. MSHA's standardized definition 

for reportable hearing loss should substantially increase the 

reporting rate of cases by mine operators, as well as improve 

the quality and usefulness of the data submitted. 

In addition to decreasing the ambient noise levels to which 

miners are exposed, miners' hearing may be conserved through 

the application of a hearing conservation program, including 

hearing protection, audiometric examinations, and worker 

training. MSHA's final noise rule requires mine operators 

to include miners exposed at or above the AL in a hearing 

conservation program. In addition to these steps to conserve 

hearing, additional steps to prevent hearing loss such as those 

described by NIOSH(') are recommended. 

In 2000, only 6.5% of the monitored miners exposed at 

or above the AL were included in a hearing conservation 

program, but by 2004,86% of sampled miners exposed above 

the AL were in a hearing conservation program. The percentage 

enrolled in HCPs did not differ substantially between underground and surface occupations. Mine operators should seek to 

include the nonenrolled miners as soon as possible to preserve 

their hearing. 

Of some note is the high level of enrollment (77% in 

2004) of sampled miners with AL noise dose less than 50%; 

enrollment of these miners in HCPs is not mandatory. Several 

potential explanations for this high participation rate include 

that the miner's assigned duties rotated among occupations 

with higher noise exposure, the mine operator was not aware 

of the actual noise dose of some occupations, and the mine 

operator included a larger population in the HCP as a benefit to 

miners or as a means to simplify compliance. The available data 

do not permit further evaluation of these or other explanations. 

MSHA's final rule requires the use of hearing protectors 

by miners when the miner's noise exposure exceeds the PEL 

during the work period until administrative and/or engineering 

controls are instituted or if controls do not reduce the exposure 

to below the PEL. Miners have used HPDs in high noise 

environments to a greater or lesser extent for many years, 

although underground miners in particular resisted the use of 

hearing protection because it reduced their ability to hear "roof 

talk." Roof talk is sound produced in the disturbed geologic 

strata, and it can provide information about the stability of the 

mine roof and walls. The use of HPDs among monitored miners 

increased from 1987 to 2004 for all exposure ranges except 

the highest (Figure 4). Substantial increases were observed in 

the use of HPDs in the 3 years following the adoption of the 

final rule in dose ranges 0-49%, 49-99%, and 99-149%. In 

2004,13% of sampled underground miners and 9% of sampled 

surface miners who were exposed to noise in excess of the PEL 

did not use hearing protection, and methods to increase the use 

of HPDs should be implemented. 

A limitation of the data is related to MSHA's compliance 

policy prior to the promulgation of the final noise rule, which 

was to adjust measured noise doses downward to account for 

protection provided by HPDs. The adjustment calculation resulted in substantial reductions of dose, so much so that inspectors reported that they sometimes chose not to sample miners 

who used HPDs. For example, a miner with a measured PEL 

dose of 200% who wore a HPD with a noise reduction rating 

of 29 dB would have been assigned an adjusted dose of 9.5%, 
which would not exceed the allowable exposure under the 

previous compliance policy. Because use of HPDs was the primary noise exposure control in coal mines prior to the current 

regulation, the mine operator would have been motivated to 

ensure hislher employees used HPDs in high noise areas. This 

practice would result in lower pre-rule measured doses because 

the miners more likely to use HPDs (i.e., those with higher 

noise exposures) may not have been selected for sampling. 

This would also skew lower the rates of HPD use prior to 2000. 

A second limitation results from the sampling strategy used 

by MSHA. The data used for this analysis were generated by 

MSHA inspectors performing compliance assessments. The 

sampled occupations were not selected randomly, workers 

may not have been selected randomly within the occupation, 

and the data include sampling done during follow-up surveys 

subsequent to identifying overexposures, although followup samples are not differentiated in the database records. 

Consequently, the data may be biased. 

A third limitation affects estimates of HPD use and enrollment in HCPs. The estimates reported here may be higher 

than actual rates and may not reflect HPDIHCP status of the 

total mining population because the estimates are based on 

miners who used HPDs and reported HCP enrollment during 

a compliance inspection. The presence of an inspector in the 

worlplace may have altered the behavior of mine operators 

and the miners with regard to these issues. 

SUMMARY AND RECOMMENDATIONS 

M SHA's current policy specifies occupations that must 

be monitored during noise inspections at surface and 

underground mines. This policy results in high sampling rates 

for some occupations with relatively lower noise exposure. 

MSHA should consider modifying its coal mine health inspection policies on selection of occupations to be sampled 

for noise exposure. A sampling policy prioritized on more 

recent historical occupation-based noise exposure data, or 

a statistically selected sample, may provide more useful 

information for compliance and epidemiologic assessments of 

noise exposure and NIHL in the coal mining industry. 

The average sound levels during a mining shift are declining 

for most coal mining occupations, but increasing shift duration 

makes it difficult to predict the effect reduced sound level will 

have on the incidence of NIHL among miners. 

Surveillance should be implemented to assess the occurrence of NIHL in coal miners using audiometric data collected 

as part of the hearing conservation programs. Analysis of 

previously collected audiometric data using the new standard 

definition of hearing loss may provide baseline information to 

improve future investigation of NIHL in coal miners. 

Miner participation in hearing conservation programs is 

high based on reports from MSHA inspectors but should be 

expanded to include all miners exposed to noise in excess 

of the action level. Use of hearing protection should also be 

expanded to include all miners where feasible administrative 

and engineering controls do not reduce noise exposure to less 

than the PEL. 

ACKNOWLEDGMENTS 

T he authors thank MSHA for granting access to the 

exposure data. We also thank John Seiler and Leonard 

Marraccini of MSHA, and R.J. Matetic, Barbara Fotta, and 

Deborah Landen of NIOSH for their helpful reviews of early 

drafts of the work. 

REFERENCES 

1. National Institute for Occupational Safety and Health (NIOSH): Criteria for a Reconznzended Standard: Occ~ipational Noise Exposure. DHHS 

(NIOSH) Publication No. 98-126. Cincinnati, Ohio: U.S. Department of 

Health and Human Services, Public Health Service, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and 

Health, 1998. 

2. National Institute for Occupational Safety and Health (NIOSH): Results froin tlze National Occ~~pational Health Survey of Mining (NOHSM). 

DHHS (NIOSH) Publication No. 96-136. Cincinnati, Ohio: US Department of Health and Human Services, Public Health Service, Centers 

for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, 1996. 

3. U.S. Department of Labor, Mine Safety and Health Administration: 

"Mining Industry Accident, Injuries, Employment, and Production Statistics, All Coal Mining Data, Table 03, Average Number of Employees 

at Coal Mines in the United States, by Primary Activity, 1978-2003" 

[Online] Available at: http://www.msha.gov/ACCINJ/ALLCOAL.htm 

(Accessed August 8,2005). 

4. "Health Standards for Occupational Noise Exposure, Final Rule," Federal 

Register 64:176 (13 Sep 1999). pp. 49548-49634. 

5. "Health Standards for Occupational Noise Exposure in Coal, Metal and 

Nonmetal Mines; Proposed Rule," Federal Register61:243 (17 Dec 1996). 

pp. 66347-66397. 

6. U.S. Department of Labor, Mine Safety and Health Administration: 

"MSHA Coal Mine Health Inspection Procedure Handbook, Chapter 

3, Noise, PH89-V- l(13)" [Online] Available at: http://www.msha.govl 

READROOM/HANDBOOK/PH89-V- 1 (chap_3)(2001).pdf (Accessed 

February 1 1,2005). 

7. U.S. Department of Labor, Mine Safety and Health Administration: 

"Mining Industry Accident, Injuries, Employment, and Production Statistics, All Coal Mining Data, Table 01 Number of Coal Operations in 

the United States, by Primary Activity, 1978-2003" [Online] Available 

at: http://www.msha.go~/STATS/PART5O/WQ/1978/wq78c101.htm (Accessed February 1 1,2005). 

8. Seiler, J.P., M.P. Valoski, and M.A. Crivaro: "Noise Exposure in U.S. 

Coal Minesy9 Informational Report (IR 1214). U.S. Department of Labor, 

Mine Safety and Health Administration, 1994. 

9. Johnson, D.L., C.W. Nixon, and M.R. Stephenson: Long-duration 

exposure to intermittent noises. Aviat. Space Environ. Med 42987-990 

(1976). 

10. Nixon, C.W., D.L, Johnson, and M.R. Stephenson; Asymptotic behavior of temporary threshold shift and recovery from 24- and 48-hour noise 

exposures. Aviat. Space Environ. Med 48:3 11-3 15 (1977).