Summary of NIOSH research completed 

on dust control methods for surface 

and underground drilling

W.R. Reed, J.M. Listak, S.J. Page and J.A. Organiscak

Mining engineer, mining engineer, research physisist and mining engineer, respectively, National Institute 

for Occupational Safety and Health, Pittsburgh Research Laboratory, (NIOSH-PRL), Pittsburgh, Pennsylvania

Abstract

NIOSH continues to conduct respirable dust control research for surface mine blasthole drilling operations. Research areas have included testing variables (shroud leakage area, drill deck cross-sectional 

area, shroud height, collector-to-bailing airflow ratio, etc.) that have the most impact on respirable dust 

control, development of a dust collector inlet hood, development of a dust collector dump point shroud 

and testing of a small-diameter water-separating sub. This paper summarizes the results of the aforementioned research that has been completed. Additionally, past dust control research for drilling operations 

of both underground and surface mines completed by the U.S. Bureau of Mines (created in 1910 and 

incorporated into NIOSH in 1997) is reviewed.

Introduction

Silicosis is an occupational disease caused by the inhalation 

of respirable crystalline silica particles that are <10 μm in diameter. There is no cure except through its prevention (Porter 

and Kaplan, 2007). Silicosis is classified as one of three types: 

chronic silicosis, which occurs after 10 or more years of exposure of relatively low respirable silica dust concentrations; 

accelerated silicosis, which develops within 5 to 10 years after 

exposure; and acute silicosis, which can occur within a time 

period of 5 years or within just a few weeks after exposure 

to high concentrations of respirable silica dust (Schulte et 

al., 2002). Symptoms for all three categories of silicosis are 

similar, with chronic silicosis being asymptomatic at first, but 

ultimately characterized by dyspnea or shortness of breath with 

exertion progressing to dyspnea at rest. Advanced cases result 

in pulmonary hypertension and respiratory failure. Symptoms 

for accelerated silicosis are similar to chronic silicosis, but 

occur over a shorter time period. Symptoms of acute silicosis 

are similar but occur rapidly and may include weight loss and 

fatigue with respiratory failure usually occurring within 2 

years (Porter and Kaplan, 2007). Additionally, once silicosis 

develops, complications may arise from mycobacterial or 

fungal infections with tuberculosis being the most common 

mycobacterial infection (Schulte et al., 2002). 

Definitive medical information about silicosis has evolved 

slowly throughout history, but the relationship between dust 

and health problems has long been recognized. Hippocrates, 

born in 460 B.C., pointed out the difficult breathing of the metal 

digger due to exposure. In the 16th century, Georgius Agricola, 

who authored the first book on physical geology, was one of 

the first to report on the effects of dust in miners. 

Scientists eventually associated dust exposure with a disease 

called “consumption,” which was characterized by symptoms 

such as slight fever, loss of appetite, cough and shortness of 

breath, ultimately leading to the victim being confined to a bed 

with great weakness, sleeplessness, fever and bloody sputnam 

until death (Harrington and Davenport, 1935). The process of 

contracting this disease was still not clearly understood during 

this time, but it was known to be prevalent in miners, smelters 

and stone masons (Harrington and Davenport, 1935).

In the early 1880s, medical science was revolutionized with 

the development of germ theory and Robert Koch’s discovery of 

the tuberculosis bacillus. With these advancements, consumption was now thought to be caused by the tuberculosis bacteria. 

Ironically, this finding set back the understanding of silicosis, 

leading to the thinking that because the tuberculosis bacteria 

caused consumption, the dust was only the carrier and caused no 

harm (Rosner and Markowitz, 1991). It was not until the early 

20th century that investigations were conducted into understanding silicosis, which is now known to be an occupational illness 

caused by a progressive fibrosis that occurs in the lungs when 

silica particles are ingested by macrophages (NIOSH, 1977).

The first investigation of silicosis in the mining industry 

in the United States occurred in 1914-1915 and examined the 

incidence of pulmonary diseases in the Joplin district of Missouri (Lanza and Higgins, 1915; Harrington and Davenport, 
1935). From this and other observations and 

studies of mining and tunneling operations, 

it was noticed that silicosis became more 

prevalent and caused more worker deaths 

when steam-driven or compressed-air 

percussive drills were introduced into the 

tunnels (Higgins et al., 1917; Cherniack, 

1986; Nelson, 2006). Because early researchers noticed that silicosis was associated with drillers, an occupation linked 

with high exposure to silica dust, the U.S. 

Bureau of Mines (USBM) initiated research 

on drilling dust control (Harrington and 

Lanza, 1921; Sayers, 1925). This research 

initiated with underground drilling operations, progressed to dust control research 

on roof bolting operations and eventually to 

surface mine drilling operations. The goal 

of the research was to determine methods 

to reduce the generation of respirable silica 

dust in the underground mine, roof bolting 

and surface mine drilling operations.

Although it is recognized that dust 

control research for drilling operations has 

been conducted by other public and private 

entities, this paper focuses on research 

conducted by the National Institute for 

Occupational Safety and Health (NIOSH) 

and the U.S. Bureau to Mines (USBM). 

The USBM was incorporated into NIOSH 

under the Centers for Disease Control and 

Prevention, U.S. Department of Health 

and Human Services, in 1997, and its dust 

control research on drilling operations 

continues under NIOSH.

Underground drilling dust control research

After the investigation of pulmonary diseases in the Joplin district of Missouri in 

1915, it was determined that dry drilling 

in unventilated underground mines was the 

most dangerous activity related to silicosis. 

As a response, the USBM began conducting research on dust 

control for drilling processes in underground mining facilities. 

From studies completed by the USBM, it was established that 

drilling vertical holes with hammer type drills produced the 

most dust (Fig. 1), with angle hole producing less.

During the 1920s, the focus was on eliminating dry drilling 

in underground mines and replacing this drilling method with 

wet drilling (Fig. 2). Measurements of dust concentrations 

that were recorded at this time showed a dramatic decrease in 

dust concentrations when wet drilling was used (Harrington, 

1922).

Figure 1 — Angle drilling in an open stope.

Figure 2 — Wet drilling in an open stope with a Leyner Drill.

Wet drilling. Wet drilling uses water in addition to compressed 

air to flush the drill cuttings from the hole. The water is forced, 

using the compressed air, through the drill steel, out the end of 

the drill bit and back through the drill hole forcing the cuttings 

out of the hole. This drilling method was found to be the best 

method of dust control with dust reductions ranging from 86% 

to 97%, depending on the type of drilling involved (Harrington, 

1921; Johnson and Agnew, 1939). This range of dust reduction 

could be lower, 50% to 60%, depending on the angle of the drill 

hole being drilled (Brown and Schrenk, 1938a). The high dust 

reductions from wet drilling were confirmed approximately 

six decades later when studies evaluated the use of water mists 

and foams injected through the drill steel, resulting in reduced 

dust concentrations by 91% to 96%, respectively (Page 1982a 

,1982b). During the early part of the 20th century, while it was 

conceded that wet drilling equipment was heavier and more 

costly to purchase and maintain, there were other advantages 

such as less drill steel breakage and greater penetration rate with 

wet drilling than with dry drilling. In fact, an example was given 

where a large copper mining company showed that the penetration rate with wet drilling was nearly twice the penetration rate 

of dry drilling (Harrington, 1921). However, it was also noted 

that there was resistance to wet drilling by the miners because 

of the fundamental working conditions it required and the large 

amounts of water used. They claimed that they would rather 

“swallow” the dust and take their chances of obtaining miner’s 

consumption rather than become “crippled with rheumatism,” as 

they would say, from the water of the drilling operations. Even 

when all drills were replaced with wet stopers, the miners would 

attempt to drill with them dry, with poor results. However, after 

the use of water with the wet stopers was compelled, eventually 

the men would become advocates of their use.
To help overcome this psychological resistance to change 

as mines were converting to wet drilling, the USBM continued 

research on the wet drilling dust control method. In 1938, a 

study was conducted drilling horizontal holes with wet drilling 

to determine penetration rate of drill bits. The results showed 

that the depths of a series of holes became progressively shorter 

due to the dulling of the drill bits (i.e., hole #1 was the deepest, with hole #3 being the shortest). This study also provided 

proof that the first 0.30 m (1 ft) or 0.60 m (2 ft) of drill hole 

was the dustiest when wet drilling (Littlefield and Schrenk, 

1938). After the first 0.30 to 0.60-m (1 to 2-ft) were completed, 

the dust concentrations dropped rapidly and maintained a 

constant level. This study also demonstrated that collaring 

the hole was not responsible for the high dust concentrations, 

because the holes were precollared prior to testing (Littlefield 

and Schrenk, 1938).

The relationship of water flow to dust concentrations was 

tested in both stoper and drifter drills. For stoper drills, as the 

water flow increased to 4.9 L/min (1.3 gpm), it was found 

that the dust concentrations decreased rapidly. Above 4.9 L/

min (1.3 gpm) the dust concentrations decreased at a slower 

rate. This phenomenon was also seen in drifter drills, but at a 

water flow rate of 3.8 L/min (1.0 gpm). Therefore, it was recommended that the minimum water flow should be 4.9 L/min 

(1.3 gpm) for stoper drills and 3.8 L/min (1.0 gpm) for drifter 

drills (Brown and Schrenk, 1938b). Eventually it was shown 

that different types of drill bits generated differing amounts of 

respirable dust when drilling dry. For example, the polycrystalline diamond compact bits generated less dust than the tungsten 

carbide bits. When wet drilling was tested, the differences in 

respirable dust generation and penetration rate were shown to 

be minor (Sundae et al., 1995). During this testing, it was also 

shown that large amounts of water are not required to produce 

good dust control and good penetration rate. A water flow rate 

of 0.41 L/min (0.11 gpm) was sufficient for dust control and 

good penetration rate (Sundae et al., 1995).

The use of “wetting” agents or additives to the water used 

in drilling was also evaluated. Results showed that wetting 

agent solutions applied at varying flow rates provided better 

dust control, reducing dust concentrations from wet drilling 

by an average reduction of 53.5% for each cubic inch of rock 

drilled (Johnson, 1943). However, the dust control provided 

by wet drilling was so good that the reduction from the use 

of wetting agent solutions was not significant in normal drilling operations. The advantage of wetting agents was in the 

improvement of penetration rate. When wetting agents were 

used, the average drilling speed or penetration rate increased 

slightly (+4.5%). However, this was shown to be highly variable with the penetration rate varying between -24.9% and 

+57.5% (Johnson, 1943). 

Dry drilling with external sprays. Although previous testing 

showed that the use of external water sprays when dry drilling 

only produced dust reductions of 25% compared to dry drilling 

alone (Harrington, 1921), a new external water spray device 

was tested in the late 1930s. This device was in the shape 

of a ring that contained spray holes on the inside diameter 

for dust control on dry drilling in quarries. This device was 

slipped over the drill steel and sprayed water on the drill steel 

outside of the hole in an attempt to reduce dust concentrations. 

Although it was an improvement over external water sprays, 

results showed that this device could not be used to replace 

wet drilling while maintaining proper dust control during 

drilling operations, because it produced dust reductions that 

were variable, ranging from 75% to 88% dust reduction over 

dry drilling (Johnson and Agnew, 1939). It was stated that the 

water spray device could be used to assist in dust control during 

wet drilling and that it would aid in reducing dust during drill 

collaring procedures. Much later, a rubber shrouded external 

spray system, depicted in Fig. 3, was shown to improve dust 

reduction to 53% (Page, 1982b) compared to 25% (Johnson 

and Agnew, 1939) from earlier external spray studies. It was 

determined that the earlier external water spray system was 

not as effective because it allowed the dust to be generated 

and entrained prior to wetting the material. Therefore, there 

was little time for the water to mix with the dust to reduce 

its concentration.

Figure 3 — External boom mounted water spray.

Roof bolting dust control research for underground coal mines

A significant amount of work has been completed on roof 

bolting dust control (Fig. 4). In the early 1950s, a survey was 

conducted of underground coal mines located in three states. 

An evaluation of these mines showed that much of the strata 

above the coal contained 7% to 88% free silica, which was 

highly variable depending upon the type of strata (Westfield 

et al., 1951). At this time, it was reported that approximately 

71% of the mines performed roof-bolting operations without 

any dust control and that dust protection relied on the use of 

respirators (Westfield et al., 1951). Meanwhile, Owings and 

Johnson (1953) reported that drilling without dust control for 

even short periods of times (7 minutes) presented a health 

hazard to the drillers and others working in the surrounding 

area. Their study showed that drillers were exposed to silica 

dust for highly variable time periods ranging from a short 

time period of 7 minutes to a longer period of 6 hours and 46 

minutes. This time period of exposure was dependent on the 

rock being drilled.

Average dust concentrations were highly variable, depending 

on the drilling operation, and ranged from 12 to 4,531 million 

particles per cubic foot of air (Owings and Johnson, 1953). In 

1935, it was stated that the U.S. Public Health Service declared 

that there was a danger in any atmosphere containing more than 

5 million particles per cubic foot of fine silica particles (<10 

μm) (Harrington and Davenport, 1935b). The USBM made the 
following recommendations for the amount of dust allowable 

in mine atmospheres (Owings and Johnson, 1953): 

“In bituminous-coal and lignite mines the average 

full-shift concentration of atmospheric dust to which a 

workman may be exposed should not exceed 20 million 

particles per cubic foot of air, and a maximum concentration for any single operation should not exceed 40 

million particles of dust per cubic foot of air. When the 

dust contains silica, no more than 5 million particles of 

silica dust per cubic foot of air should be present in the 

above limiting concentrations. The dust count may be 

multiplied by the percentage of silica concentration, and 

if the result is less than 5 million the dust concentration 

will be considered safe. The above limiting concentrations are based on impinger samples in which light-field 

counts are made under a microscope.”

In 1952, the American Conference of Industrial Hygienists 

adopted the threshold limits shown in Table 1 for silica dust 

during a working shift (Owings and Johnson, 1953)

It was not until 1969 that an official legally recognized 

dust standard was adopted in the United States; a permissible 

shift exposure limit of 2.0 mg/m3 of airborne respirable dust 

for coal mine workers — if more than 5% quartz mass is determined to be in the coal mine worker dust sample, then the 

applicable respirable dust standard is reduced to the quotient 

of 10 divided by the percentage of quartz in the dust (Parobeck 

and Tomb, 2000).

Table 1 — Threshold limits for mineral dust.

 Million particles of dust 

 Silica content per cubic foot of air

High (above 50% free SiO2) 5

 Medium (5% to 50% free SiO2) 20

 Low (below 5% free SiO2) 50

 Total Dust (below 5% free SiO2) 50

Wet drilling. Conclusions from testing were that all powered 

drilling produced excessive amounts of dust, best controlled 

at its source through dust collection or wet drilling, similar to 

the standard practice in metal mines using pneumatic percussion drills. It was also advised to avoid dry collaring holes 

— drilling the first 50 mm (2 in.) of hole with the water valve 

off — as this produces high dust concentrations. Additionally, proper ventilation was recommended in that wet drilling, 

while it reduces dust concentrations significantly, it does not 

completely eliminate the generation of dust. The practice of 

using respirators and allowing the dust to escape the drilling 

operation was not recommended, because workmen other than 

the drillers could be exposed to the dust as it was transported 

via the ventilation system. Additionally, it was recognized 

that prolonged use of a respirator would be uncomfortable to 

workers (Owings and Johnson, 1953). 

Figure 4 — Permissible roof-bolting drill capable of drilling 

vertical or angle holes.

Dust collection systems. When problems occurred with wet 

drilling in underground mines due to roof rock swelling when 

exposed to the water, resulting in roof falls and comfort issues 

for the operator such as the water running down from the hole 

onto the driller, the use of dry drilling with dust collectors was 

preferred. Dust collectors use some type of an exhaust ventilation system near the source of the dust. This can be a successful method of dust control for drilling, but many operational 

problems have been encountered that have undermined full 

acceptance of this dust control method. The USBM started a 

program in 1950 to evaluate dust-collection systems for roof 

drilling in underground coal mines. A typical dust collection 

system is shown in Fig. 5.

To properly design a dust-collection system it must:

 • be capable of handling both fine and large material, as 

drilling in hard roof produces fine material and drilling 

in soft roof produces coarser material;

 • take full advantage of gravity to move the drilling cuttings from the hole; and

 • have a tight seal where the drill steel passes through the 

hood of the collector (this was found to be more important 

than the seal between the hood and the roof rock).

Also, for a dust collection system to be approved, it could 

not allow the dust concentration to be more than 10 million 

particles of dust per cubic foot of air (Owings, 1956). The 

only drawback to using dust collectors was that they had to 

be properly maintained for them to work properly. 

Additional research focused on the effect of the placement 

of the roof bolter in comparison with the entire section, on 

the proper cleaning of the filter boxes, and on the creation of 

an air canopy to provide fresh air to the bolter operator. One 

study showed that the roof bolter operating downwind of the 

continuous miner could be exposed to high concentrations of 

respirable silica dust (up to 204 μm/m3 in the bolter intake), 

especially if the miner is cutting rock (Goodman and Organiscak, 2003). On the other hand, it was shown that when the roof 

bolter operates upwind of a continuous miner using poor dust 

control practices, then the continuous miner operator can be 

exposed to concentrations up to 103 μg/m3. Proper cleaning 

of the filter boxes was also deemed to be necessary to reduce 

respirable-dust generation from the roof bolter. In fact, dust 

concentrations ranging from 103 to 327 μm/m3 were observed 

from a roof bolter when the filter boxes were not properly 

maintained (Goodman and Organiscak, 2003). 

Air canopy system. The air canopy is a device located above 

the roof bolter operator’s position that directs filtered air over the 
operator. Testing of the device confirmed that high air velocities 

were provided at a center location of the air canopy. These high 

air velocities also decreased rapidly as the distance away from 

the canopy was increased, which would result in lower protection. When using the canopy, respirable dust reductions of up 

to 56% to 62% were demonstrated. These reductions reduced 

rapidly when an interference air velocity was increased (i.e., 

airflow velocities of the ventilating air). When the ventilating 

air velocity increased then the respirable dust reductions of the 

canopy ranged from approximately 25% to 28% (Goodman 

and Organiscak, 2001). This canopy showed potential as an 

additional engineering control that could provide protection 

against respirable dust in areas of low-velocity ventilation air. 

Research on an improved air canopy is continuing.

Figure 5 — Testing a Browning dust collector.

Surface drilling dust control research

Drilling boreholes is an ancient activity: the Egyptians are 

thought to have used corundum dust or pebbles to drill holes in 

rock, while the Chinese are mentioned as using coupled bamboo 

rods for drilling deep holes for water by lifting, dropping, and 

rotating the rods (McGregor, 1967). Mechanized drilling was 

introduced in the 1800s when the first steam-driven rotary rock 

drill was built. In the late 1800s, compressed air was used for 

operating rock drills in tunnels with the pneumatic rock drill 

being produced by 1900. For surface operations, churn drilling — where the drill bit is picked up and dropped numerous 

times through a cable or drill pipe to drill the hole — was the 

most common drilling method continuing through mid-1950 

(Fig. 6). The first roller bit was used in America around 1900. 

In 1910, Hughes improved rotary drilling by perfecting the 

tricone bit, although tungsten carbide was not in pervasive 

use until 1940 (McGregor, 1967). Mechanical rock drilling 

continued to evolve throughout the 20th century, from churn 

drilling to rotary and percussion drilling, to produce the diesel 

and electrically powered drilling rigs (both rotary and percussion) in use today.

Figure 6 — A Bucyrus-Erie churn drill.

The most common drilling methods in use in the mining 

industry today are percussion, rotary and down-the-hole hammer 

drilling. Percussion drilling is appropriate for small diameter 

holes (<100 mm (4 in.)) and has a limited depth of penetration 

into a rock formation. This type of drilling is also not suited 

for soft sticky material as the bit can penetrate too deeply with 

each impact that can impair rotation of the drill (McGregor, 

1967). Rotary drilling is applicable for large-diameter drilling at considerable depths; however, rotary drilling demands 

large amounts of down pressure, requiring large heavy drills to 

maintain penetration rates (Lyons, 2001). Recently, down-thehole hammer drilling has become more prevalent than rotary 

drilling, as it requires less down pressure to maintain similar 

penetration rates. However, this drilling method has the same 

disadvantage as percussion drilling when drilling in soft sticky 

materials (McGregor, 1967; Lyons, 2001).

Curiously, the USBM did not conduct surface mine dust 

control research until mid-1980, when MSHA identified the 

highwall driller and driller’s helper occupation as those with 

the highest exposure to silica dust. Prior to 1960, churn drilling was a common surface drilling practice, but it had slow 

penetration and therefore did not generate the large volumes 

of dust seen in today’s rotary or percussion drills. However, 

many of the prior research findings established for dust control 

in underground mining can be applied to 

surface mining and thus they form the basis 

for surface drilling research. 

Dust sources and transport.The USBM’s 

first studies on surface drilling focused on 

determining the locations of dust generation 

on a blasthole drill rig. From dust concentration measurements made on the drill, 

it was determined that up to 90% of the 

respirable dust was generated from three 

locations (Fig. 7): the dust collector dump 

(38%), leakage through the drill shroud 

(28%) and through the table bushing (24%) 

(Maksimovic and Page, 1985). The other 

10% of respirable dust emanated from other 

nearby mining operations. Instantaneous 

respirable dust concentrations showed 

that peak concentrations could reach 68 

mg/m3 for the dust collector dump and 98 
mg/m3 for the drill shroud and table bushing (Maksimovic 

and Page, 1985).

Figure 7 — Blasthole drill showing sources of dust emissions.

Further testing was completed to determine the range of 

transport of respirable dust from surface drilling operations. 

Dust sampling systems were set up around and away from the 

drill at varying distances. In addition, gas samplers were used 

at these locations to isolate dust contamination from other 

nearby sources. Sulfur hexafluoride (SF6) gas was released 

at the drill during drilling, and the sampling stations sampled 

for both the SF6 gas and respirable dust. Results showed that 

within 76 m (250 ft) of the drill, the combination of dust and 

gas concentrations transported to downwind personnel was 

insignificant. Additionally, the amount of respirable dust 

concentrations generated from drilling decreased rapidly with 

distance. However, the vertical positioning of the drill may 

influence the downwind exposure to personnel in the surrounding area (Page and Maksimovic, 1987).

Wet drilling.As with underground drilling operations, surface 

mine blasthole drilling using wet drilling techniques provided 

the best dust control. Wet drilling provided dust control efficiencies of up to 97% at a water flow rate of 4.5 L/min (1.2 

gpm). As seen in Fig. 8, the dust control efficiencies greatly 

increased from 0.8 L/min (0.2 gpm) to 2.3 L/min (0.6 gpm), 

then leveled off above this flow rate. However, for the drill 

tested, once the flow rate approached 3.8 L/min (1.0 gpm), 

operational problems were encountered such as the drill bit 

plugging and the drill steel rotation binding (Page, 1987). 

Another disadvantage of wet drilling is that it degrades the 

tri-cone roller drill bits and shortens their lives by 50% or more. 

Therefore, the USBM tested a water separator sub for dust 

control efficiency and its effect on drill bit life (Fig. 9). A water 

separator sub uses inertia to remove the injected water from the 

bailing air. This removed water is then ejected out through weep 

holes into the annulus above the drill bit. Testing demonstrated 

that dust control efficiencies of up to 98% could be obtained 

using the water separator sub while dust control efficiencies of 

wet drilling without the water separator sub were 96%. Most 

importantly, the use of the water separator sub increased bit 

life. Data gathered by the USBM from a mine where drilling 

occurred in monzonite, sandstone, limestone and iron ore over 

a 14-year period showed that drill bit life averaged 590 m/bit 

(1,938 ft/bit) with wet drilling without water separation. With 

water separation, the drill bit life increased to an average of 

approximately 2,743 m/bit (9,000 ft/bit) (Page, 1988).

Further work on water separator subs did not continue until 

recently when the issue reemerged to examine the use of water 

separator subs in small diameter drill holes of 171 mm (63⁄4 

in.). Testing full-production drilling with this small diameter 

water separator sub could not be accomplished at the test site. 

Therefore, an analysis of the impact this water separator sub 

would have on drill bit life was not possible. Nevertheless, 

test results and visual observations showed that dust reductions similar to those attained with previous water separator 

subs were achievable. However, operational problems were 

encountered during the testing of the sub, which included 

regulation of water flow and the condition of the overburden. 

It was difficult to maintain constant water flow because the 

pressurization of the water tank changed as the water level in the 

tank changed, requiring constant adjustment of the water flow 

to the sub. The ground conditions at the test site included highly 

weathered and fractured material. When drilling occurred, 

the high-pressure water ejecting from the weep holes caused 

deterioration and spalling of the wall material of the drill hole, 

which led to hole cave-in. However, in a recent study, it was 

determined that these problems could be overcome, in which 

case the small diameter water separator sub showed potential 

to be very effective for dust control (Listak and Reed, 2007).

Figure 8 — Relationship of waterflow rate to dust control 

efficiency for surface mine drilling .

Dry Drilling. Dry dust collection systems are used when 

drilling dry. The collection systems tested work well and can 

be up to 99% efficient, but maintaining a proper seal between 

the ground and the bottom of the shroud is paramount, and this 

can be difficult due to uneven ground surfaces. Testing demonstrated that dust control efficiencies for the dust collection 

system became progressively worse (from 99% to 31%) as the 

gap between the bottom of the shroud and the ground surface 

increased (from 0 to 690 mm (27-in.)). Therefore, guidelines 

for proper shroud design were developed as follows: that its 

internal volume should be 1.8 times the volume of the hole, 

that the length and width of the shroud should be 2.5 times 

the shroud height, and that the dust collection system should 

maintain a negative pressure of 0.5 mbar (0.2 in. H2O) underneath the shroud (Page, 1987).

It was also shown that keeping the drill deck shroud in 
good condition, minimizing any leakage, was beneficial for 

dust control. By minimizing the leakage, the dust collector 

was able to properly perform its job of removing dust from 

underneath the shroud. Additionally, increasing the airflow of 

the dust collector improved dust control. Airflows of the dust 

collector that approached eight times the amount of airflow of 

the bailing air (air used to flush cuttings from the drill hole) 

significantly reduced dust leakage from the drill deck shroud 

(Organiscak and Page, 1995). However, common collector to 

bailing airflow ratios encountered in the field can be up to 3:1 

with 2:1 generally being the norm when the filters are loaded 

(Page and Organiscak, 2004). 

Figure 9 — Water separator sub with rotary bit.

To determine optimum collector airflow to bailing airflow 

ratios, investigations were performed in an experimental laboratory of a simulated drill deck model (Fig. 10). This simulated 

drill deck was modeled after those decks normally found on 

medium-sized rock drills that drill holes ranging from 127 to 

203 mm (5 to 8 in.) in diameter. It was located centrally inside 

a larger chamber used for dust containment. The simulated 

drill deck had an adjustable shroud that allowed the leakage 

between the bottom of the shroud and the ground to be varied. 

Tests were conducted by varying collector airflows and shroud 

leakages while maintaining a constant bailing airflow. Results 

showed that the most important factors for optimal dust reduction were to simultaneously minimize shroud leakage and 

maintain high collector airflows (>3:1) in relation to bailing 

airflows (Page and Organiscak, 2004).

Figure 10 — Drill deck testing facility at NIOSH showing 

simulated drill deck inside dust chamber.

To reduce the emissions of dust from the table bushing in 

the drill deck, a device called the air-ring seal was developed. 

This device is a donut-shaped manifold with closely spaced 

holes, which produce high-velocity jets of air, on the inside 

perimeter of the donut. It has a large inside diameter to accommodate the passing of the drill bit, steel, and table bushing 

through its center. The air-ring seal is housed underneath the 

drill deck at the location of the table bushing. Air pressure is 

supplied to the air-ring seal from the existing air compressor 

system, which produces the high-velocity air jets that impede 

the transport of dust through the table bushing. The air-ring 

seal was shown to reduce dust by 50% to 60%. It also had the 

advantage of preventing material from traveling through the 

table bushing, therefore allowing the drill deck to be kept clean 

of drill cuttings (Page, 1991).

Moving the inlet closer to the drill steel was also studied. 

The problem incurred with moving the inlet is that the larger 

drill cutting particles could enter the dust collection system, 

causing obstruction problems. Laboratory tests were conducted 

using a rubber deflection seal located below the new inlet location and surrounding the drill stem. This was shown to be 

successful in preventing large particles from entering the collection system (Organiscak and Page, 2005). However, drilling 

oftentimes requires high ground clearance underneath the drill 

shroud, and this inlet design protruded significantly below the 

drill deck. Therefore, a low-profile inlet hood was tested. This 

design was tested at different collector airflows and different 

shroud leakage areas. Results showed that collector airflows 

and shroud leakage areas had the predominant impact on dust 

generation. However, the newly designed inlet hood reduced 

dust generation by 63% to 91% for the scenarios with the 

higher collector airflows and also the higher shroud leakage 

areas, showing dramatic improvement over the original inlet 

location (Organiscak and Page, 2005).

The promising results above led to field evaluation of the 

new inlet hood design. However, because the drills tested with 

the new design had shrouds that were properly designed and 

maintained, no noticeable differences in dust concentrations 

were noted from the original design to the new inlet hood 

design. Therefore, its effectiveness in the field could not be 

evaluated. There was also an unforeseen problem with the 

new design — it eventually became obstructed from the drill 

cuttings entering the inlet hood. This problem could be easily 

rectified by designing the hood to empty the cuttings when the 

drill mast is lowered. 

Dust collector dust control

A method of dust control for the dust collector dump that was 

tested early, once surface mine drilling was recognized as a 

silica hazard, was using a pelletizer that was attached to the 

drill. This apparatus used water at a rate of 0.4 L/min (0.1 gpm) 

to agglomerate the fine-sized dump material into pellets that 

ranged from 1 to 10 mm in diameter. This reduced dust levels 

by 65% to 73% at the collector dump. However, there were 

several problems encountered from having to meter the correct 

amount of water to the large size of the system, degrading the 

mobility of the drill (Bailey and Page, 1987).

Additional controls were evaluated by testing their performance on truck-mounted drill rigs. One control was to inject 

water into the exhaust of the dust collector. The type tested 
was a Rotoclone collection system. Modifying the exhaust to 

a level or downward position, attaching a 6-m (20-ft) length 

of reinforced flex tubing to relocate the exhaust port to the rear 

of the drill and injecting water at a rate of 0.8 L/min (0.2 gpm) 

resulted in a 92% reduction of respirable dust (Organiscak and 

Page, 1995). A disadvantage of this system is the need to supply 

water for injection. Another disadvantage is the bulkiness of 

the large amount of flex tubing required to relocate the exhaust 

port. Besides injecting the water into the exhaust port of the dust 

collector, the movement of the exhaust port itself was shown to 

be an effective dust control for the drill operator. The vertical 

exhaust port was extended vertically by adding a 2.4-m (8-ft) 

section of pipe. This did not reduce the dust concentrations 

but did allow the dust to be transported and dispersed away 

from the operators. Reductions in dust concentrations by 62% 

were seen at a 30.5-m (100-ft) distance away from the drilling 

operation (Organiscak and Page, 1995).

Another simplistic dust control was to shroud the dust collector discharge from the discharge opening to the ground (Fig. 11). 

Using a simple device as a shroud resulted in dust reductions of 

80% from this source (Organiscak and Page, 1995). This shroud 

is easy to install. Basically, a piece of brattice cloth is attached 

over the existing rubber boot to the dust collector dump point 

using a large hose clamp. The length of brattice cloth (or similar 

material) should be sufficient to allow it to extend from the dust 

collector dump point to the ground. It should be cut so that it 

is only long enough to just touch the ground when the drill is 

lowered. When wrapping the cloth around the dust collector 

dump, the overlap should be placed so that it is on the outside 

of the dust collector dump (it should be visible as the installer 

looks directly at the dust collector dump). This overlap allows 

the cloth to expand as fine material is dumped to the ground, 

while containing the entrained respirable fraction within its 

confines. Placement of the overlap on the outside also keeps the 

fine material off the drill tracks, which otherwise could cause 

re-entrainment of the respirable size fraction of the material 

when the drill starts in motion.

This dust collector dump shroud is very effective in reducing 

the respirable dust. Respirable dust concentrations measured 

after installation of the dust collector shroud ranged from 0.16 

to 0.24 mg/m3, demonstrating a reduction of respirable dust 

of 63% to 88%. This reduction is highly dependent on wind 

direction and wind speed (Reed et al., 2004). Advantages of 

this method of respirable dust reduction are that the material is 

inexpensive and requires almost no maintenance. If the shroud 

becomes damaged, it can easily be replaced in 10 to 15 minutes, 

requiring little, if any, downtime for the drill.

Additional dust control measures. Further investigations 

revealed that the operator could reduce his exposure to dust 

simply by being positioned in such a way as to avoid the dust 

clouds. By standing away from the drill during its operation 

and only approaching it for operational purposes, such as maintaining drilling operations, changing steel, etc., the operator 

can significantly reduce the exposure (Organiscak and Page, 

1995; Zimmer, 1997).

A study on the drill operating parameters was initiated to 

evaluate the drill bit rotation in relation to silica generation. 

The premise was that high-speed rotation of the drill bit may 

produce more silica in the dust emitted from the drill hole 

due to the regrinding of material in the hole. Results from this 

study showed that at 100 rpm (normal operating rotation), the 

average percent silica of all the drill holes was approximately 

22.1%. When the rotation was slowed to 80 rpm, the average 

percent silica dropped to approximately 19.2%. This showed 

a slight reduction of silica generation when slowing the drill 

bit rotation (Listak, 2003). Additional findings were that the 

amount of silica in the airborne samples was generally less than 

half the silica amounts in the bulk material from the drill hole, 

demonstrating that not all of the silica in the rock is liberated 

as airborne respirable dust (Listak, 2003).

Figure 11 — Dust collector dump point shroud.

Conclusion

USBM research for dust control in drilling operations was 

initiated early after the creation of the USBM in 1910. This 

research was first conducted on underground drilling operations 

as these seemed to be associated with most cases of silicosis in 

underground drillers. Findings were that wet drilling is the best 

control method to reduce respirable silica dust. Other studies 

showed that the most dust was generated in the first 0.30 to 

0.60 m (1 to 2 ft) of a drill hole, that water flow rates did not 

have to be high to successfully reduce dust generation and that 

external water sprays did not perform as well as wet drilling.

Later, studies of coal mine roof bolting operations were 

conducted that evaluated the silica content of the surrounding strata, showing that it could vary from 7% to 88%. Again, 

wet drilling was shown to be the best dust control measure, as 

dry drilling for even short time periods could expose workers 

to high levels of respirable silica dust. Additional research 

presented other methods, such as the use of dust collectors 

and their proper maintenance, the optimal placement of the 

operators with respect to the dust-generating sources and an 

air canopy to provide filtered air to the roof bolter operator, 

which could be used to provide further protection to workers 

against respirable silica dust.

Surface mine blasthole drill dust control research was initiated later in mid-1980. Prior to this time, the surface blasthole 

drill did not represent a concern for high levels of respirable 

silica dust. As noted above, wet drilling provided the best 

reduction of respirable silica dust, up to 97% reduction, but it 

reduced the life of the rotary bits. The first step in the research 

was to determine that the dust emissions were located at three 

sources on the drill: the deck shroud (28%), the table bushing (24%) and the dust collector dumping operation (38%). 
Follow-up research focused on reducing the respirable dust 

concentrations at these locations. The important initiative in 

drill shroud design was the elimination of any shroud leakage 

by preventing gaps between the ground surface and the bottom 

of the shroud and at the corners of the drill deck. Additionally, by keeping the collector airflow at three to four times the 

bailing airflow, the amount of respirable dust generated at this 

location was significantly reduced. Other projects to reduce 

dust at the shroud location examined the use of a water separator sub and moving the collector inlet closer to the drill steel. 

The water separator sub showed potential, but problems were 

encountered with water control and loose material issues that 

were later overcome. The collector inlet relocation was also 

successful but required redesign to prevent large particles from 

collecting and obstructing airflow in the inlet area.

Research focusing on the elimination of respirable dust from 

the dust collector included the use of a pelletizer to agglomerate 

the collector fine material, injecting water at the dust collector exhaust, and the use of a dust collector dump shroud. The 

pelletizer was successful in reducing respirable dust by 65% 

to 73% but had the disadvantages of being a large, bulky and 

high-maintenance addition to the drill. Injecting water at the 

dust collector exhaust was also successful, but the required use 

of water introduced drawbacks, such as the need to refill and 

freezing issues in the winter. The dust collector dump point 

shroud was successful in reducing dust by 63% to 88% and 

was simple to install, requiring almost no maintenance.

Dust control research for drilling operations continues at 

NIOSH, looking for new and improved methods to reduce 

respirable silica dust to operators and surrounding personnel. 

Some of the future dust control research projects are evaluating air nozzle-assisted dust capture underneath the drill shroud 

and further dust control techniques for the dust collector dump 

material. Results from these projects should produce additional 

methodologies to further control dust from drilling operations, 

thereby, providing additional protections to the drill operators 

and surrounding personnel from respirable silica dust.

References

Bailey, P.J., and Page, S.J., 1987, “Agglomeration of Collected Drill Dust,” U.S. 

Bureau of Mines Contract No. SO368000 (April).

Brown, C.E., and Schrenk, H.H., 1938a, “Effect of Angle of Drilling on Dust Dissemination.” U.S. Bureau of Mines Report of Investigation 3381 (February).

Brown, C.E., and Schrenk, H.H., 1938b, “Relation of Dust Dissemination to 

Water Flow Through Rock Drills,” U.S. Bureau of Mines Report of Investigation 3393 (April).

Goodman, G.V.R., and Organiscak, J.A., 2001, “Laboratory evaluation of a canopy 

air curtain for controlling occupational exposures of roof bolters,” Proceedings of the 7th International Mine Ventilation Congress, June 17-22, Cracow, 

Poland. Wasilewski, S., ed., pp. 299-305.

Goodman, G.V.R., and Organiscak, J.A., 2003, “Assessment of respirable quartz 

dust exposure at roof bolters in underground coal mining,” Journal of the 

Mine Ventilation Society of South Africa, April/June, pp. 50-54.

Johnson, J.A., 1943, “Use of Wetting Agents in Reducing Dust Produced by 

Wet Drilling in Basalt,” U.S. Bureau of Mines Report of Investigation 3678 

(January).

Johnson, J.A., and Agnew, W.G., 1939, “Dust produced by drilling when water 

is sprayed on the outside of the drill steel,” U.S. Bureau of Mines Report of 

Investigation 3478 (October).

Harrington, D., 1921, “Dust Reduction by Wet Stopers,” U.S. Bureau of Mines 

Report of Investigation 2291 (November).

Harrington, D., 1922, “Drilling and the Dustiness of Metal-Mine Air.” U.S. Bureau 

of Mines Report of Investigation 2339 (March).

Harrington, D., and Davenport, S.J., 1935a, “Review of Literature on Effects of 

Breathing Dusts with Special Reference to Silicosis.” U.S. Bureau of Mines 

Information Circular 6835 (March).

Harrington, D., and Davenport, S.J., 1935b, “Review of Literature on Effects of 

Breathing Dusts with Special Reference to Silicosis.” U.S. Bureau of Mines 

Information Circular 6857 (October).

Harrington, D., and Lanza, A.J., 1921, “Miners’ Consumption in the Mines of 

Butte, Montana,” U.S. Bureau of Mines Technical Paper 260.

Higgins, E., Lanza, A.J., Laney, F.B., and Rice, G.S., 1917, “Siliceous Dust in 

Relation to Pulmonary Disease Among Miners in the Joplin District, Missouri,” U.S. Bureau of Mines Bulletin 132.

Lanza, A.J., and Higgins, E., 1915, “Pulmonary Disease Among Miners in the 

Joplin District, Missouri,” U.S Bureau of Mines Technical Paper 105.

Listak, J.M., 2003, “Method to determine the effects of rotary drilling parameters and overburden rock on silica-dust generation,” Preprint No. 03-136, 

presented at the SME Annual Meeting, Feb. 24-26, 2003, Cincinnati, Ohio, 

pp. 102-106.

Listak, J.M., and Reed, W.R., 2007, “Water separator shows potential for reducing respirable dust generated on small-diameter rotary blasthole drills,” 

International Journal of Mining, Reclamation, and Environment, Vol. 21, No. 

3, pp. 160-172 (September).

Littlefield, J.B., and Schrenk, H.H., 1938, “Relation of Dust Concentration to 

Depth of Hole During Wet Drilling,” U.S. Bureau of Mines Report of Investigation 3369 (January).

Lyons, W.C., Guo, B., and Seidel, F.A., 2001, Air and Gas Drilling Manual, 2nd

Edition, McGraw-Hill.

Maksimovic, S.D., and Page, S.J., 1985, “Quartz Dust Sources During Overburden Drilling at Surface Coal Mines.” U.S. Bureau of Mines Information 

Circular 9056 (January).

McGregor, K., 1967, The Drilling of Rock, London: CR Books Ltd. (A Maclaren 

Company).

Nelson, S.R., 2006, Steel Drivin’ Man – John Henry, The Untold Story of an 

American Legend, Oxford University Press.

NIOSH, 1977, “Occupational diseases: a guide to their recognition (Revised),” 

DHEW (NIOSH) Publication No. 77-181, U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National 

Institute for Occupational Safety and Health.

Organiscak, J.A., and Page, S.J., 1995, “Assessment of Airborne Dust Generated from Small Truck-Mounted Rock Drills,” U.S. Bureau of Mines Report 

of Investigations 9616.

Organiscak, J.A., and Page, S.J., 2005, “Development of a dust collector inlet 

hood for enhanced surface mine drill dust capture,” International Journal of 

Surface Mining, Reclamation, and Environment, Vol. 19, No. 1, pp. 12-28.

Owings, C.W., 1956, “Dust Control in Mining, Tunneling, and Quarrying in the 

United States,” U.S. Bureau of Mines Information Circular 7760 (October).

Owings, C.W., and Johnson, L., 1953, “A Study to Determine Potential Dust 

Exposure in Connection with Intermittent Rock Drilling in Coal Mines.” U.S. 

Bureau of Mines Report of Investigation 5004 (October).

Page, S.J., 1982a, “Evaluation of the Use of Foam for Dust Control on Face Drills 

and Crushers,” U.S. Bureau of Mines Report of Investigation 8595.

Page, S.J., 1982b, “An Evaluation of Three Wet Dust Control Techniques for 

Face Drills,” U.S. Bureau of Mines Report of Investigation 8596.

Page, S.J., 1987, “Optimizing Dust Control on Surface Coal Mine Drills,” U.S. 

Bureau of Mines Technology News, No. 286 (September).

Page, S.J., 1988, “Impact of Drill Stem Water Separation on Dust Control for 

Surface Coal Mines.” U.S. Bureau of Mines Technology News, No. 308 

(August).

Page, S.J., 1991, “Respirable dust control on overburden drills at surface mines,” 

in Presentation/Proceedings of the 1991 American Mining Congress Coal Convention, Surface Mining II Session, Pittsburgh, Pennsylvania, pp. 523-539.

Page, S.J., and Maksimovic, S.D., 1987, “transport of respirable dust from 

overburden drilling at surface coal mines,” Proceedings of the 3rd Mine 

Ventilation Symposium, pp. 625-639.

Page, S.J., and Organiscak, J.A., 2004, “Semi-empirical model for predicting 

surface coal mine drill respirable dust emissions,” International Journal of 

Surface Mining, Reclamation, and Environment, Vol. 18, No. 1, pp. 42-59.

Parobeck, P.S, and Tomb, T.F., 2005, “MSHA’s programs to quantify the crystalline silica content of respirable mine dust samples,” Preprint No. 00-159, 

presented at the 2000 SME annual Meeting and Exhibit, February 28-March1, 

Salt Lake City, Utah, 5 pp.

Porter, R.S., and Kaplan, J.L., eds., 2007, The Merck Manual of Diagnosis and 

Therapy, Online Edition, Access at www.merk.com/mmpe/index.html, Merck 

Research Laboratories.

Reed, W.R., Organiscak, J.A., and Page, S., 2004, “New approach controls 

dust at the dust collector dump point, NIOSH finds a simple, cost-effective 

solution for reducing dust for blasthole drills,” Coal Age, Vol. 109, No. 6, 

pp. 20-22 (June).

Rosner, D., and Markowitz, G., 1991, Deadly Dust, Silicosis and the Politics of 

Occupational Disease in 20th Century America, Princeton University Press.

Sayers, R.R., 1925, “Silicosis Among Miners,” U.S. Bureau of Mines Technical 

Paper 372.

Schulte, P.A., Rice, F.L., Key-Schwartz, R.J., Bartley, D.L., Baron, P.A., Schlecht, 

P.C., Gressel, M.G., and Echt, A.S., 2002, NIOSH Hazard Review: Health Effects of Occupational Exposure to Respirable Crystalline Silica, DHHS (NIOSH) 

Publication No. 2002-129, www.cdc.gov/niosh/02-129A.html, Department 

of Health and Human Services, Centers for Disease Control and Prevention, 

National Institute for Occupational Safety and Health (April).

Sundae, L.S., Summers, D.A., Wright, D., and Cantrell, B.K., 1995, “The Reduction of Airborne Dust Generated by Roof Bolt Drill Bits Through the use of 

Water,” U.S. Bureau of Mines Report of Investigation 9594.

Unger, H.F., and Fumanti, R.R., 1972, “Percussive Drilling with Independent 

Rotation,” U.S. Bureau of Mines Report of Investigation 7692.

Westfield, J, Anderson, F.G., Owings, C.W., Harmon, J.P., and Johnson, L., 

1951, “Roof Bolting and Dust Control,” U.S. Bureau of Mines Information 

Circular 7615 (August).

Zimmer, 1997, “Comparative evaluation of dust control technologies on percussion rock-drilling rigs. Case studies,” Applied Occupation and Environmental 

Hygiene, Tharr, D., ed.,Vol. 12, No. 12, pp. 782-788.