Characteristics of Fugitive Dust Generated 

from Unpaved Mine Haulage Roads 

JOHN A. ORGANISCAK 1

I Address correspondence to: John A. Organiscak. Pitlsburgh Research Laboratory. Department of Health 

and Human Services. Centers for Disease Contm] and Prevention. National Institute for Occupational 

Safety and Health. PO. Box 18070. Pitlsburgh. PA 15236. USA. Tel.: +1-412-386-6675: Fax: +1-412-386­

4917; E-mail: jd03@cdc.gov 

AND W.M. RANDOLPH REED2 

'National Institute for Occupational Safety and Health. Pillsburgh. PA. USA. 

ABSTRACT 

Fugitive dust is generated along unpaved mine roads from intermitlent equipment traffic. Typically. the 

majority of such traffic consists of trucks hauling either mine product or waste from the surface mine pit 

andlor the processing plant. Fugitive dust generated along these unpaved mine roads includes particles of all 

sizes which become airborne. The potential hazards include the deleterious effects to human health of 

inhaled dust. traffic visibility hazards and environmental impacts on the localized area by the larger-sized 

viSIble airborne dust. Two field surveys were recently conducted to quantify fugitive dust generation and 

dispersion from truck traffic on unpaved and untreated mine haulage roads. For these surveys. airborne dust 

sampling was conducted at multiple sampling locations away from an unpaved haulage road at a limestone 

quarry/plaot and at a coal mine preparation plant to measure the size characteristics. concentrations and 

dispersive behavior of the dust cloud generated fmm truck traftic. Results show that at least 80% of the 

airborne dust generated by haul trucks was larger than 10 J.lm. Airborne respirable. thoracic. and total dust 

concentrations all decreased and approached backgmund concentrations 30.5 m (100 feet) from the mad. 

This report describes the average and instantaneous peak dust levels that were measured up to 30.5 m 

(100 feet) from the haulage road. 

I. INTRODUCTION 

Airborne dust is generated from various processes conducted at surface mining and 

mineral preparation operations. These various processes may include drilling, 

blasting, bulldozing, loading, transporting, dumping, crushing and processing mine 

ore and waste rock. The airborne dust generated can be composed of visible and 

invisible particulates as seen by the naked eye and can possess a significant amount of 

dust concentration spatial variation around the dust source. In the mining industry, 
prolonged exposure to airborne respirable coal dust and/or silica dust has been 

found to be responsible for the prevalence of occupational lung disease in mine 

workers [I, 2]. 

The U.S. Mine Safety and Health Administration (MSHA) enacts and enforces 

mine worker safety and health standards to mitigate mine worker injuries and 

occupational diseases. MSHA's permissible shift exposure limit is 2.0 mg/m3 of 

airborne respirable dust for coal mine workers as defined by the Mining Research 

Establishment (MRE) criteria [3]. Ifmore than 5% quartz mass is determined to be in 

the coal mine worker dust sample using MSHA's P7 infrared method [4], the 

applicable respirable dust standard is reduced to the quotient of 10 divided by the 

percentage of quartz in the dust. MSHA's nuisance dust limit (total dust) for noncoal miners is 10 mg/m3 as defined by the American Conference of Governmental 

Industrial Hygienists (ACGIH) [3]. If more than I% quartz mass is determined to be 

in the non-coal mine worker dust sample using NIOSH's X-ray method [4], the 

applicable standard is now a respirable dust standard of 10, di vided by the total of 

the quartz percentage, plus 2. Both of these dust standards are designed to limit 

worker respirable crystalline silica (quartz) exposure to 0.1 mg/m3 or less, per shift. 

Compliance with these dust standards is expected to reduce a worker's risk of 

occupational lung disease over an average life expectancy. Coal miner chest X-ray 

surveillance has shown a noticeable reduction in the prevalence of coal workers' 

pneumoconiosis (CWP) under the federal coal mine dust standards, but the incidence 

of CWP has not been eliminated [I]. 

Mine worker overexposure to the reduced dust standard due to quartz remains an 

ongoing problem at mining operations in the United States. The percentage of MSHA 

dust samples from 1996 to 2000 that were above the respirable dust standard due to 

quartz were 12.8% fur sand and gravel mines, 12.9% for stune mines, 16.4% for nonmetal mines, 17.6% for metal operations, and 19% for coal mines [5]. At surface 

mining operations, the occupations that have the highest frequency of exceeding the 

respirable dust standard are operators of mechanized equipment such as drills, 

bulldozers, scrapers, front-end loaders, haul trucks, and crushers [5, 6]. Most of the 

airborne dust generated is generally localized to a region where the equipment is 

operating, so dust control technology can be engineered to the particular process or 

environment of the equipment operator [7]. However, fugitive dust generated along 

unpaved haulage roads from truck traffic can encompass larger regions of the mine, 

possibly exposing other workers or neighboring residences to airborne dust when 

downwind of the haulage roads. 

The most common method of fugitive dust control is road surface welting, but 

others include adding hygroscopic salts, surfactants, soil cements, bitumens and films 

(polymers) to the road surface [7-10]. Although these road treatment methods have 

been shown to be effective, their application generally involves a continual maintenance process due to road degradation from traffic, dry climatic conditions, and 
material spillage on the road. Thus, some fugitive dust generation may be inevitable 

during the operation, until road maintenance is addressed. 

The purpose of this study was to measure the size characteristics, concentrations, 

and spatial variation of airborne dust generated along unpaved and untreated mine 

haulage roads to examine the potential human health and safety impacts of adjoining 

areas around the road. Total, thoracic, and respirable airborne dust concentrations 

were measured with personal dust sampling equipment. Dust sampling was conducted 

at multiple locations - next to, 15.2 m (50 Ft), and 30.5 m (100 ft) away from the 

haulage road - to examine the airborne dust behavior as it was transported away from 

the road by the wind. Multiple stage personal impactors were also used at several 

locations near the road and at 15.2 m (50 ft) from the road to detennine the relative 

mass size distribution of the dust generated. Field surveys were conducted along the 

road of a limestone quarry and along the road of a waste dump at a coal preparation 

plant. The study did not encompass any larger regional U.S. Environmental Protection 

Agency's (EPA) high volume particulate matter (PM) type area sampling at the 

mines' property boundaries. This report describes the details of this study and the 

results attained. 

2. FIELD SAMPLING APPROACH 

Dust sampling surveys were conducted along an unpaved haulage road at a limestone 

quarry in Virginia and at a coal preparation plant in Pennsylvania. Sampling was 

conducted during 3-day shifts for each mining operation in July and August of 2002. 

The limestone quarry had mostly multiple rear-axle on-road trucks and some off-road 

trucks passing through the test section in both directions. The coal preparation plant 

had a loop traffic pattern with only loaded off-road trucks passing through the test 

section on their way to the dump site. Since both of these operations routinely watered 

their haulage roads, a 91.4 m (300 ft) test section of unpaved road was not routinely 

watered during the sampling shift. Dust sampling was conducted along the middle 

30.5 m (100 feet) of the 91.4 m (300 ft) test section of road. On several occasions, the 

road section was wetted prior to the dust sampling period and then dried out during 

the sampling shift. Weather conditions while sampling were generally hot and dry 

with a variety of clear sunny skies to overcast cloud cover. 

To classify the size of dust generated and its spatial variability around the road, 

size-selective airborne area dust sampling was conducted at multiple locations away 

from the road. Side-by-side sampling of total, thoracic, and respirable dust was conducted at each location away from the road. Total, thoracic, and respirable airborne 

dust samples were each collected on 37 mm PVC filter cassettes using MSHA Elf 

personal sampling pumps calibrated to the desired tlow rate of the particular dust 

sampling classifier. Total airborne dust was collected without a classifier by sampling 
at 1.7 Llmin using only a closed-face 37 mm filter casselle. These samplers are 

commonly used to measure personal inhalable fractions of dust (O:S; aerodynamic 

diameter:S; 100 11m). However, when used as area samplers, their performance is 

dependent on wind velocity. as are other inhalable sampler designs [II]. The total 

dust samples tend to undersample the larger sized inhalable fractions of dust 

(aerodynamic diameter> 41 11m). as defined by the American Conference of 

Governmental Industrial Hygienists (ACGIH) [II]. Thoracic and respirable airborne 

dust concentrations were measured with reasonable agreement to the American 

Conference of Governmental Industrial Hygienists' (ACGIH) particle size-selective 

sampling criteria for airborne particulate matter [12]. BGI, Inc. GK2.69 cyclones 

were operated at 1.6 L/min to collect the thoracic fraction of airborne dust, having a 

median aerodynamic diameter defined as 10 11m [13]. DOff-Oliver 10 mm nylon 

cyclones were operated at 1.7 Llmin to collect the respirable fraction of airborne dust, 

having a median aerodynamic diameter defined as 4 11m [14, 15 J. 

Instantaneous respirable dust samplers and multi-stage impactors were also used 

during the study to examine real-time dust behavior and relative size distribution of 

the dust, respectively. Instantaneous respirable dust levels were measured wIth 

Thermo-Anderson/MIE Personal DataRAMs (PDR) (Franklin, MA) actively sampling at 1.7 Llmin with a Dorr-Oliver 10 mm nylon cyclone placed upstream and 

a 37 mm final filter cassette downstream of the light-scattering sample chamber. 

Instantaneous respirable dust levels were adjusted by a calibration factor, determined 

by the ratio of the average gravimetric concentration to the time-weighted average 

of instantaneous dust levels measured with the PDR. The instantaneous measurements were electronically logged every 2 s in the DataRAM's internal memory 

for subsequent computer retrieval and analysis. Relative size distributions were 

determined using Sierra 290 series personal sampling impactors operating at 

2.0 Llmin at several locations. Cut stages I through 6 were used. The impactor 

size cut stages measured at 2.0 Llmin correspond to 21.3 11m, 14.8 11m, 9.8 11m, 

6.0 11m, 3.5 11m, and 1.55 11m aerodynamic diameters with smaller-sized particulates 

collected on a final filter [16]. 

Dust concentration spatial variation around the road was measured by placing the 

dust samplers on tripod-supported stands over a 7-location sampling grid. The tripod 

stands were extended to their maximum height of approximately 1.5 m (5 ft). Figure I 

shows the general layout of this sampling glid with respect to the expected wind 

direction. Since the winds are generally from the west, one tripod was positioned on 

the west berm side (upwind) of the road and the other 6 tripods were positioned along 

the east berm side (downwind) of the road, at locations next to, 15.2 m (50 ft) away 

and 30.5 m (100 ft) away from the road. The 15.2 m (50 ft) and 30.5 m (100 ft) east 

berm side tripods were placed in an uncut grassy field that was approximately 0.9 m 

(3 ft) high (mid-thigh level). The tripods were spaced 30.5 m (100 ft) along the road 

with a Young wind speed and direction instrument (Model 06201 Wind Tracker, 
Traverse City. Michigan) located at the center of the 30.5 m (100 ft) by 30.5 m (100 ft) 

grid. Wind data were recorded at 30 s intervals with Metrosonics 331 data loggers 

(Rochester. NY). Each type of dust sampling instrument described above was used at 

all the sampling locations with the exception of the Sierra 290 impactors; they were 

only used at locations A, B, and C. 

Headwind 

.ito road 

I

"­

"-,,­

"-~ 15.2 m 

15.2m 

Road orientation 

Limestone quarry-N20"E,
 

coal plant-NIO"E
 

Wind monitor 

Dust 

sampling 

station 

C 

•

Fig. I. Field sampling layout adjacem to haul road. 

Other data collected during the surveys included traffic time study information, 

truck speed, road surface parameters, and silica dust content. The time study was 

conducted recording the time that trucks and other vehicles exited the sampling grid 

along the road. About half of the trucks were timed with a stopwatch as they passed 

the 30.5 m (100ft) distance between sampling stations Band E to determine their 

average travel speed. Approximately 1kg or more of road surface material was 

collected each day by sweeping up smaller samples of surface material from several 

spots across the road. The road surface material was analyzed for percentage of silt 

content (particle sizes s: 75 11m) [17], total moisture percent (mass basis) [18], specific 

gravity [19] and quartz content (X-ray method 7500) [20]. The airborne thoracic and 

respirable dust samples at sampling location B were also analyzed for quartz content 

by X-ray method 7500. The minimum airborne dust sample mass analyzed for quartz 

under this study was selected to be 0.2 mg. The side-by-side respirable dust samples 

(tilters) from the personal sampler and the PDR were typically combined to achieve 

more than 0.2 mg of dust mass for quartz analysis. Thoracic dust samples generally 

had more than 0.4 mg of mass and could be analyzed individually. Many of the dust 

samples collected at other locations away from the road had lower masses and they 

were not analyzed for quartz content. 
3. FIELD SURVEY RESULTS 

The data collected from these two field studies have been summarized using general 

descriptive statistics, linear regressions, and selected days of instantaneous respirable 

dust data. The data analysis results are presented in numerous figures and a table 

which are briefly described below. Figures 2 and 3, respectively, show the airborne 

dust concentration statistics for the limestone quarry (LQ) and the coal plant (CP). 

These figures show the dust concentration means and standard deviations as 

categorized by their various distances from the road. 

0.0 

0.5 

2.0 t-----------i c:: 

:8 

f! 1.5 +-----t------r-l 'E 

fll: 1.0 +-----n:r--------, o 

u 

14 

::J 

C 

West berm East berm East 15.2 m East 30.5 m 

Road sampler locations 

Fig. 2. Average road dust concentrations at the limestone quarry. 

o Respirable 

+-----t-------I-----­.Thoracic -----I 

+----r+-,---------j------ ElTotal 

Resp. background - 0.04 mglm3 

... 3.0 E 

"al E 2.5 

c:: 

0 2.0 :;:::: 

III

.. 1.5 'E 

CIl 

u 1.0 l: 

0 

u 0.5 

14 

::J 

c 0.0

West berm East berm East 15.2 m East 30.5 m 

Road sampler locations 

Fig. 3. Average road dust concenlrJlions al the coal preparation plant. 

Figure 4 shows the daily wind 

speed and direction data measured at the limestone quarry (LQ) and the coal plant 

(CP), presented by the median and the 10 to 90 percentile range. Figure 5 shows the 
instantaneous respirable dust levels for the LQ at location B and the wind data during a 

shift when the road was initially wet in the morning and dried out by early aftellloon on 

July 16, 2002. 

+ Median with 10-90 percentile range 

« Direct wind direction at samplers 

1 

I I I 

1 t t 

I I I 

Q 0 0 0 

:0 :0 :0 '" '"

Q '"

Q '" '" '" ...., :0 :0 :0 '" '" '" CD j:2 al « « « 

§ § § 11. 11. 11. '" '" CD 

U U U 

360 +---+---+---+---+---+-------1 '5
 

270 11.'''-::::..::·1.-:::-::::-::::-::::-:::t-::-::::-..- _........-t-...._..t_o_·+...._
 ..::-><:c"--p_·--.-------,,------1
 

c t t o 180 +--+--+----------1"----+--I 

:g 90 +----------------+---j 'tI
 

C
 

0-'------------------------'

Fig. 4. Wind speed and direction data for both surveys. 

Figure 6 shows the PDR time related average instantaneous respirable 

dust concentrations and upper confidence levels (95%) measured at sampling stations 

B, C, and D for 51 trucks at the CP on August 2, 2002. These time related average 

concentration and upper confidence level curves were calculated from instantaneous 

concentrations measured every 2 s over identical 1.5 min time periods when each truck 

passed the sampling grid. Figures 7 and 8 show the relationships between side-by-side 

airborne respirable. thoracic, and total dust concentrations at the LQ and CP 

operations, respectively. Figure 9 shows the cumulative aerodynamic diameter size 

distribution statistics (mean and standard deviation) measured with the impactors at 

both operations. Table I shows the road surface and dust content analysis data. 

Instantaneous dust data were not analyzed for truck type, speed, or load status, since 

distance, wind and road surface conditions (wet/dry) appeared to be the most dominant 

survey variables affecting dust concentrations along the road during this study. 

Results from both the LQ and CP surveys show that a majority of the airbollle dust 

generated by trucks was non-respirable, with all airborne dust concentrations notably 
decreasing at the further distances from the road. Figures 2 and 3 show the numeric 

average and standard deviation of the gravimetric dust concentrations measured at 

various distances from the road for the three days of sampling at the LQ and CPo 

respectively. A respirable background dust level is also shown on each figure, 

determined from averaging all the PDR instantaneous dust concentrations when there 

was no traffic activity. Total and thoracic dust concentrations were notably higher than 

the respirable dust concentrations at all locations. Also, the dust concentrations 

diminished most noticeably from the east-berm to the 15.2 m (50 ft) locations with a 

further reduction at the 30.5 m (100 ft) locations. The dust concentrations at the LQ 

were generally higher than at the CP, but a significantly larger number of trucks 

passed through the LQ test section, 230 to 308 daily, as compared to the CP which had 

47 to 64 trucks (see Table I). 

f--­

I 1 fL III I .I~ II. I II I~ III 11.J w 

12 

10 

E 

Ii 8 

ii 6 :I 

".. 

ii 4 

l!! 

is.

:: 2 II: 

o 

10:00:01 11:00:01 12:00:01 13:00:01 14:00:01 15:00:01 16:00:01 

Time. hr:min:sec 

360 +---'---+--........--+----'---+-........--t----L---t-----'---+ 20
 

r. 

'S 

E 270 

o~r: 

0 180 U 

f! 

'6 

" 90 c: 

i 

-tt----I-#Iii-+-Hf-lf-P-IetH"t-.lo-+-if---JlI----1I-t---'--l--ti--'--'-1tIfH+----'+--++--t-tt-tt--m-101.. 

"

c: 

i 

.... --. Direction --Speed - - Direct wind direction at samplers 

Fig. 5. tnstantaneous dust and wind data at the limestone quarry. 

During the LQ survey the winds mostly came out of the southwest towards the 

sampling grid, with wind speeds commonly between 0.2 (0.4) and 3.0 m/s (6.6 mph) 
(see Fig. 4). The winds for the CP survey were more variable, ranging from out of the 

northeast to the southwest direction at speeds between 0.4 m/s (0.8 mph) and 4.0 m/s 

(9.0 mph) (see Fig. 4). Although the west berm sampling location was located on the 

side of the road most likely upwind. this sampling location was observed to be exposed 

to some of the dust plume spanning the width of the road behind the trucks and the 

occasional wind directional shifts towards the west berm side of the road. 

--Avg@B ,B·95%UCL --Avg@C 

C-95%UCL Avg@D D-95%UCL '"E <- - - - - Time truck exited samp,ing grid
 

E
 

0. 

r" " 

C 

o . .. 

l! 1-----"'IHnH ' ,...... • 

C 

U 

QI nn:'/ \', C 

o 

u
 

'5i
 / '\..', 1:1 1,-­ , ... , 

:c

QI 

.. '---'-'-'---"-~'_ .. .~,,~.~,~... ,_ .... --. l! ..... ,.

'Q. 

III 

-15 o 15 30 45 60 75 

Time period around truck passage, sec. 

Fig. 6. Average of instantaneous truck dust levds at the coal preparation plant. 

Thoracic • Total--- - .. Linear (Thoracic) - •. - Linear (Total) 

..
 y = (10.81+1.83)x + (0.10+0.30) '" .","
 R 2 = 0.89 '" 

•

• • • .._--_.-------. -----_. .­ -....'"

• '" '" 

'" 

.. ­ =-y =(3.98±0.52)x - (0.OhO.08) 

R2 e-"'--­ =0.93

'" • 

6.0 

E 

C 5.0 

4.0 c 

tlc 3.0 

8 

iii 2.0 

u 1.0 

U 

l! 

o 0.0 .: 

I- 0.00 0.10 0.20 0.30 0.40 0.50 

Respirable concentration, mg/m3• 

Fig. 7. Dusl concentration relationships at the limestone quarry. 

At the LQ, the 

wind direction tended to be mostly in the direction of the east berm side of the road and 
is reflected in the higher concentrations on that side of the road (see Figs. 2 and 4). The 

wind was more spread out in all directions with respect to the road at the CP and is 

reflected in similar dust concentrations on both sides of the road (see Figs. 3 and 4). 

----- -- ---

'" 4 Thoracic • Total Linear (Thoracic) - - . - Linear (Total) -i 3.0 

E 

y =(8.07±1.29)x + (0.12±0.43) 

R 2 =0.90 -- --- --- - -- --If -

7' 

.. - • - ... .....

!! -i" • ..-' I~ • 

,~, _.~ • 

•

r: 2.5 

o 

2.0 - e 

GI 

g 1.5 

o 

u 

1.0 •

• . .

0.5 .~

R2 

o = 0.88 0.0 

-

---- • -

• 

..-.~ • • 

y = (3.29±0.58)x + (0.05±0.09) 

.c: 

I­ 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 

Respirable dust concentration, mglm3. 

I-,g.~. Uust concenlrat,on relationships at the coal preparation plant. 

--+--LQ·A - •• LQ-B - -. - ·LQ·C ----*-'CP-A -;t-CP-B - •• CP-C 

60 

c

.. 50 

= III 

III 40 .!! 

G) 30 > 

ii 20 '3 

E 

E 10 :::J 

0 0 

0 5 10 15 20 25 

Impactor cut size, 11m 

Fig. 9. Impaclor cumulative size dislribUlion data. 

The highest standard deviations for the dust concentrations occurred next to the 

road at the source of generation. A notable amount of this variation was likely caused 

by wind variability and changing road surface conditions. The wind variability for 
Tobie I. Airborne dust and bulk rood surfoce material onolysis. 

Sample analysis Limestone quarry (LQ) Coal plant (CPI 

16 July 2002 

308 trucks 

24.(, ± O. 7km/hr 

17 July 2002 

2(,3 trucks 

266 ± O. 7kill/hI' 

18 July 2002 

230 trucks 

24.(, ± O. 7kill/hI' 

2 August 2002 

57 trucks 

24.8 ± 1.2 kill/hI' 

5 August 2002 

47 Trucks 

21.7± l.7klll/hr 

6 August 

(,4 Tru

280 ± O. 9 

Respirable dust 

quartz content ('Ic r' 

Thoracic dust quartz 

content (%1" 

Bulk road surface 

quartz content ('Ic) 

Bulk road surface 

silt. ex WI. <:: 75 !lm (ex) 

Bulk road surface 

total moisture ('7<.) 

Bulk road surface 

specific gravity 

8.0" 

4.1" 

2.0 

27.0 

0.26 

2.85 

3.3" 

3.1 

2.9 

20.3 

0.17 

2.85 

16.4 

4.4" 

3.2 

19.5 

0.06 

2.87 

12.7 

22.3 

17.0 

21.2 

0.65 

2.44 

NA 

NA 

NA 

26.2 

0.68 

2.49 

9.7

20.5 

15.0 

18.3 

0.5

2.5

NOTe. "Samples analyzed from sampling station B. 

"Quartz mass in sample between the level of quantification (0.03 mg) and detection (O.Olmgl. 

Bold numbers - sample masses analyzed were between 0.2 and 0.26 mg. 

NA - Not analyzed. 
both surveys can be seen in Figure 4. The instantaneous respirable dust level response 

to wind variation and road condition can be seen in Figure 5 for sampling location B 

on July 16. On this day. the road test section was wetted before dust sampling began 

and dried out by noon. The amount of respirable dust generated in the morning of the 

day was negligible compared to the much higher concentrations measured in the 

afternoon when the road was drier. In the afternoon, the instantaneous peak dust levels 

were highly variable and are reflective of the changing wind conditions, especially 

wind direction. with respect to the sampling location. As the wind blew the road 

generated dust towards the sampling location, the dust levels increased, while they 

decreased as the wind blew dust away from the sampling location. 

Instantaneous dust concentration variation for truck passage notably diminishes 

with increased distance from the road. Figure 6 illustrates this, showing average instantaneous respirable dust cuncentrations with 95% upper confidence levels measured for 51 trucks over identical 1.5 min periods at location B, C, and D at the CP on 

August 2. Truck passage at this mine could be individually isolated into equal time 

periods, and on this particular day the wind was mostly directional towards the 

sampling grid on the east berm side of the road. As can be seen from this figure, the 

dust concentration quickly peaked next to the road (location B) as the trucks passed 

and quickly decayed as the dust cloud passed the sampler location. The dust concentrations measured further back from the road (location C - 15.2 m (50 ft), location 

D - 30.5 m (100 ft» were notably lower with a less distinguished peak. Also, truck-totruck dust concentration variation was further reduced at greater distances from the 

road as illustrated by the lower upper-confidence levels measured further from the 

road. Dust concentrations at all three locations converged to near background levels 

within a minute after the truck passed. Thus, the dust generated by the trucks was 

quickly diluted and diffused over the 30.5 m (100 ft) distance from the road. 

Although the dust concentration was notably reduced with distance from the road, 

the relative airborne size makeup of the dust was similar over the 30.5 m (100ft) 

distance from the road. Figures 7 and 8 show the respirable-to-thoracic and 

respirable-to-total dust concentration associations for all sampling locations at the 

LQ and CP, respectively. As can be seen in these figures, there were reasonably 

guod linear relationships between the different size classification concentrations. 

Linear regression model parameters and their 95% confidence levels are shown next 

to the line of best fit with its coefficient of determination (R\ These relationships 

show that, on average, the thoracic dust concentration was 4 and 3.3 times higher 

than the respirable dust cuncentration for the LQ and CP, respectively. The total dust 

concentration was, on average, 10.8 and 8.1 times higher than the respirable 

concentration for the LQ and CP, respectively. All the linear relationships had intercept parameters near zero and explained 88% or more of the data (R2

, which is the 

proportion of variation in y that can be explained by x). Given the model parameters 

confidence levels, the relationships observed at both mines were reasonably similar. 
The airborne dust mass size distributions measured with the impactors confirmed 

that a large portion of the dust mass was composed of particles greater than I0 ~m.

Figure 9 shows the average cumulative dust size distributions with standard 

deviations for the various sampling locations at both mines. The size distributions 

were fairly similar, with more closely aligned distributions measured at the same 

sampling location at each mine site. At least 80% of the dust mass was composed 

of dust particles larger than I0 ~m (aerodynamic diameter) with geometric mean 

mass diameters greater than 20 ~m (50% less or greater than). Thus, these data 

also confirm that most of the airborne dust mass generated by trucks was nonrespirable. 

The bulk road surface material analysis shows similarities in silt size content and 

bulk specific gravity between the mine sites, but also indicates notable differences in 

the silica content. Table I shows the sample analysis of bulk road surface material and 

airborne dust. All the road surface samples were collected at about the mid-afternoon 

of the sampling shifts when the roads were observed to be dry and dusty. They were 

well celow the 2% total moisture content believed necessary to control the fugitive 

road dust [9]. The silt content of the samples was comparable for both mine sites, 

ranging between 18.3 and 27%. The bulk specific gravity was slightly higher, and the 

total moisture content was slightly lower for the LQ road surface as compared to the 

CP road surface. The most significant differences in the road surface material were 

that the CP road surface had notably higher silica content percentages, ranging 

between 15 and 17%, as compared to the LQ road surface, ranging between 2 and 

3.2%. This could be attributed to the different materials used to construct the road 

surface bed. The LQ used limestone material and the CP used coal mine waste rock, 

likely composed of shale and mudstone that was mined with the coal. 

The silica content measured in the airborne dust was not always consistent with 

what was measured in the road surface material. From Table I it can be observed 

that the thoracic dust had slightly higher but relatively consistent quartz content in 

comparison to the road surface material. However, the silica content in the respirable 

dust was quite variable as compared to the quartz content in the thoracic and road 

surface material. Part of this inconsistency can be attributed to the lower respirable 

mass weights analyzed. Respirable dust samples analyzed had about half of the 

weight of the thoracic samples analyzed. with several samples having between 0.2 

and 0.26 mg of mass. Given that the silica masses (masses ranging from 0.02 to 

0.04 mg) measured on all respirable dust samples analyzed were below, to slightly 

above, the level of quantification (0.03 mgl, the accuracy of the determined silica 

content percentages is suspect at the lower sample masses analyzed (bolded numbers 

in table). This is due to the propagation of error of smaller gravimetric measurements 

used in detenllinations of quartz percentage [21]. Since all the thoracic samples 

analyzed had masses greater than 0.4 mg, there is much more certainty in their 

accuracy. 
4. DISCUSSION 

The scope of this study was limited to the examination of wind, distance, and road 

treatment condition on the generation and behavior of fugitive dust by haulage trucks. 

This study showed that reasonably high peak levels of respirable dust were generated 

next to the untreated haul road and these peak levels decreased rapidly to near 

background levels as the dust cloud moved 30.5 m (100 ft) from the road. This study 

also showed that, on average, the thoracic and total dust concentrations measured 

were about 3 to 4 times higher and 8 to II times higher, respectively, than the 

respirable dust concentrations measured. Thus, both peak thoracic and total dust 

concentrations would be expected to be much higher and behave similarly to the 

instantaneous respirable dust levels measured at, and away from, the road. These high 

levels of airborne dust generated provide the potential for high personal dust exposure 

levels near the trucks. 

Since the truck-generated dust appears to dilute and diffuse rapidly away from the 

road, the most susceptible persons for exposure are the truck workers themselves. 

Exposure is not as likely from their own truck, but from dust plumes of opposing truck 

traffic and when following behind trucks in the same direction. Between 4.4 and 9.7% 

of MSHA truck driver dust samples collected across all the mining sectors exceed the 

respirable dust standard from 1996-2000 [5]. Other occupations that can be exposed 

to fugitive truck dust are the operators of shovels and front-end loaders that fill the 

trucks and bulldozer and crusher operators that may be working in the close proximity 

to the dump, processing, and storage facilities. 

Since surface mine facilities are dynamic operations exposed to changing weather 

conditions, day-to-day dust levels can be highly variable. However, several general 

precepts can be followed to assist with maintaining worker exposures below mandated 

standards. It is desirable to use multiple dust control practices to compensate for 

operational anomalies that may make some of the individual dust control practices 

ineffective at times. The first line of control should be a method targeted at reducing dust 

generation at the source, such as road treatment. As illustrated in Figure 5 and other 

fugitive dust studies, this practice is very effective [7-10]. Road treatment also has 

secondary benefits of reducing environmental pollution in the surrounding area. 

Secondly, environmentally controlled operator cabs should be used on the mobile 

mining equipment. Environmental controls not only include heating and airconditioning capabilities, but a good external air filtration system positively pressurizing 

the interior of a well-sealed cab [22, 231. The air filtration system should be capable of 

efficiently removing inhalable dust down into the respirable size range. Many original 

equipment manufacturers (OEMs) offer these systems, while other companies offer 

retrofit systems for existing cabs. Finally, road layout and traffic patterns that can be 

economically incorporated into the mine plan should isolate the dust sources from other 

workers. An example of this would be one-way loop type haulage routes as practiced at 
the CP operation during this study. This layout can eliminate opposing traffic exposure 

to dust with the side benefit of reducing haulage accidents. 

One attribute of both mine dust sampling surveys that could not be assessed as a 

control factor on the airborne dust behavior away from the road was the thigh-high 

grassy meadow. This attribute is only mentioned because of the noticeable coating of 

fugitive dust that was on the grass. This is likely from normal fallout of the larger dust 

particles over the 30.5 m ( I00 ft) distance from the road. Other researchers developing 

computational Lagrangian fluid particle models for particulate matter dispersion in 

localized regions have predicted considerable differences in vertical dispersion of dust 

concentrations generated at 5 m above the ground level due to wind velocity boundary 

layer effects [24]. Ground-level wind velocity boundary profiles are dependent on a 

roughness length or ground surface factor. affecting the vertical component of 

particulate dispersion and horizontal settling distance. Notable vertical particulate 

dispersion effects were modeled over larger horizontal distances 100 m (328 ft) than 

those sampled in this study 30.5 m (100 ft). Additional studies would be needed to 

determine the extent of regional dust control effects from vegetation around ground 

sources of generation. 

5. CONCLUSIONS 

This truck haulage dust study showed that primarily wind, distance, and road 

treatment condition notably affected the dust concentrations measured next to. 15.2 m 

(50 fl), and 30.5 m (100 ft) away from the unpaved haulage road. Airborne dust 

measured along unpaved haul roads at a limestone quarry and coal preparation plant 

showed that high concentrations of fugitive dust can be generated with the concentrations rapidly decreasing to nearly background levels within 30.5 m (100 ft) of 

the road. Total. thoracic, and respirable gravimetric dust measurements showed the 

highest concentrations near the road with a rapid decrease in concentrations out to 

30.5 m (100 ft) of the road. 

Instantaneous respirable dust measurements illustrated that the trucks generate a 

real-time dust cloud that has a peak concentration with a time-related decay rate as the 

dust moves past the sampling locations. The respirable dust concentrations and peak 

levels were notably diminished as the dust cloud was transported, diluted, and 

diffused by the wind over the 30.5 m (100 ft) distance from the road. Individual truck 

concentrations and peak levels measured next to the dry road surface test section were 

quite variable and dependent on wind conditions, particularly wind direction, with 

respect to reaching the sampling location. Instantaneous dust measurements on one 

particular day also demonstrated that road wetting was very effective in suppressing 

the respirable dust generated by the haulage trucks, negating the factors of wind and 

distance on airborne dust concentrations. 
The vast majority of the fugitive airborne dust generated from unpaved and 

untreated haulage roads was non-respirable. At least 80% of the airborne dust 

sampled by impactors was larger than 10 ~tm (aerodynamic diameter size). This was 

also reflected in the thoracic and total concentrations, which were from 3 to 4 times 

higher and 8 to II times higher, respectively, than the respirable dust concentrations 

for this study. 

The quartz content of the road surface material for each mine was found to be 

reflective of the quartz content found in the thoracic dust samples. Quartz content 

inconsistencies for the respirable dust samples are suspect because of lower masses 

analyzed. Other road surface and truck variable factor effects on airborne dust 

generation and behavior could not easily be differentiated from the primary effects of 

wind, distance, and road treatment condition. 

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