Water separator shows potential for reducing 

respirable dust generated on small-diameter rotary 

blasthole drills 

J. M. LISTAK and W. R. REED 

Pittsburgh Research Laboratory, Department of Health and Human Services, 


Centers for Disease Control and Prevention, National Institute for Occupational 


Safety and Health, PO Box 18070, Pittsburgh, PA 15236, USA 


Drilling with water has the potential to significantly reduce the respirable dust 

concentrations generated from small-diameter rotary drills when drilling 

blastholes on surface mining operations. However, water adverseky affects tricone drill bits commonly used in surface drilling operations, causing excessive 

wear and premature replacement. Consequently, dry drilling with a dust 

collector system has the most widespread use in the industry. Tests have been 

conducted by the National Institute of Occupational Safety and Health 

(NOSH), Pittsburgh Research Laboratory (PRL) on a newly designed device 

for smaller diameter drills that separates the water from the bailing air before it 

reaches the bit and thus provides the cost benefit of dry drilling while providing 

the benefit of wet drilling for dust suppression. The water that is delivered to the 

hole with the bailing air is separated from the air by a proprietary mechanical 

device that is encased in a drill sub (short section of drill rod/pipe) located 

immediately behind the cutting bit. A cascade cyclone and a real-time dust 

monitor were used to sample dust emissions from the holes. Dust concentrations 

and silica content were measured when drilling dry versus drilling wet. The tests 

show that drilling with this water separating sub can reduce both measured dust 

emissions from the boreholes and visible dust around the drill rig. 

Keywords: Surface drilling; Respirable dust; Wet drilling; Water separator 

1. Introduction 

Dust generated from the drilling of blastholes by rotary drills at surface mining operations may 

contain harmful amounts of respirable silica dust. Overexposure to respirable (<10 pm in 

aerodynamic diameter) silica dust can lead to workers developing silicosis, a debilitating and 

potentially fatal disease that causes scar tissue in the lungs and reduces lung capacity. 
Additionally, the Internationd Agency for Research on Cancer (URC) classified silica as a 

carcinogen (IARC 1987, 1997). The regulatory standard for cod mine dust exposure in 

underground and surfacemints is 2.0 mg/rn3'whtnthe silica content in a dust sample is 5% or less. 

When the silica content is greater than 5% in the sample, the standard is reduccd by dividing the 

number 10 by the percentage of silica in the sample. 

Between the years 1985 and 1992, the Mine Safety and Health Administration (MSHA) 

collected and analystd respirable dust samplesfor silica content on all surface mine occupations. 

The results show that, of all surface mine occupations sampled, the drill operator and drill heIptr 

had the highest permntage of samples containing greater than 5% silica, 81% and 88% 

respectively (Tomb et d. 1995). This is further supported by the National Institute for 

Occupational Safety and Health (NIOSH), which confirmed that mining machine operators 

accounted for the highest incidence of silicosis-related deaths from 1990 to 1999 (MOSH 2003). 

More recentIy, drill operator sampla collected by MSHA between the years 2000to 2004showed 

that 14% exceed the permissible exposure limit. Because of the threats they pose to employees' 

heal& these occupations have been the focus of dust mitigation research. 

Most blasthole rotary drilI rigs use dust collectors to capture dust emissions,During drilling, 

dry cornpremed air (bailing air) travels to the bit'throughthe drill pipe. The bailing air, which exits 

from the nozzles at the bit, keeps the bit cool, flushes the cuttings from around the bit, and forces 

the cuttings up the hole, expelling them at the surface. Larp amounts of dust can be produced 

during the drilling process and dust collectors, operating under optimum conditions, BX used to 

maintain dust concentrations to a safe level. 

The dust collectors are vacuum systems that are mounted on the drills and consist of a fan, 

filters, a collectot tube and a shrouded did1 deck over the hole. These systems draw dust 

emissions from beneath the shrouded drill deck as they exit the hole. Figure 1 shows rht layout 

of a typical dust collector mounted on a surface blastholc drill. The drill deck and shroud, which 

encIose the drill hole, are connected to the dust collector unit by a collector tube. The fan in the 

wllectar unit creates negative pressure within the shrouded deck area to remwe the dust from 

3.-
 ??., q 3 

Figure I. Dust collecror on a surface mine blasthole drill, 
underneath the deck into the collector as the dust is being Bushed from the hale. Onet inside the 

dust coll~ctor,the dust-ladm air passes through filter media for dust removal, and the filtered 

air is then expelled into the atmosphere. To prevent the filters from cloggmg, the filters are 

periodically clemed by back-flushing with compmsed air. The dust that is dmed from the 

filters falls into the collector dump and exits the collactor unit by mas of a chute onto the 

ground. 


Whtn new and maintained, dry dust collectors can effectively achieve greater than 95% 

respirable dust removal under optimum operating conditions. However, as operating pararnetws 

changeand dust colhction syatems degrade,the effectiveness of these colIactors has bten shown to 

fall below 42% in dust removal eBciency (Zhmer and Lutck 1986). Dust escaping the dry 

collector unit can be traced to several sources (Organiscak and Page 2005). Damaged or nonfunctional filters will result in dust-laden air reaching thc fan. CoIlcctor system enclosurt 

components,whose primary purpose is to wpture and contain the dust, can cause dust leakage 

when the components arc damaged or worn, Dust leakages also can oacur from the shroud md 

the drill table bushing, resulting in over half of the dry dust emisaiom from the collection system 

. (Mahhovic and Page 1985). In figure 1, the dust shroud is not making a good seal with the 

ground and dust can be seen escaping from the shroud area. 

Mous studiai have shown the effectiveness of controlling dust from surface mine blastholes 

by drilling with water. A cohort mortality study ofsand workws in North.America (Rando st al. 

2001) showed that a change from dry drilling to wet drilling was one of the common process 

changes that reduced historical exposure to silica in the sand industry. A study by the US Bureau 

of Mines (1988) showed the potential bmeh of wet suppression drilling on large-diameter 

blasthole rotary drilIs at surface coal minea, It was reported that the wattr injection method of 

dust control showed substantid reduction in the amouit of respirable dust emanating from the 

holes,with rtspirable dust control efficiencies ranging from 94 to 99%. 

Despite its proven effectiveness, there are disadvantages to wet drilling with tri-cone bits. In 

northern regions where temperahum fall below freezing, drilling with water could be a problem 

during winter months, However, additives that prevent the fredng of water in tank arc 

available. Although not tested in this study, ethyltnc glycol and propylene glycol are both used 

in antifrem solutions. According to the Agency for Toxic Substances and m e Regisby 

(ATSDR),the Food and Drug Administration (FDA) has classified propylcne glycol as WI 

additive that is 'generally recognized as safe' for usein food (ATSDR 1997). The Department of 

Health and Human Services, IARC and the Environmental Protection Agency @PA) have nut 

classified ethylme glycol or propylenc glycol for carcinogenicity (ASDR 1996),Wet drilling also 

causa premature rotary drill bit degradation and failure as a result of the corrosive process of 

hydrogen embrittlcmcnt (an'event that occurs with the ingress of hydrogen into a component). 

This process reduces the ductility and load-baring capacity, and causes cracking and 

catastrophic failure at stresses below the normal yield stme of he affected material. To 

overcome the prqture bit failure caused by wet drilling, a mechanical device to separate the 

water from the air was tested and shown to be effective in keeping injected water from reaching 

the bit page at al. 1988). The device, a drill sub lo~,teddirectly behind the bit, usw the high 

ineha of the water to separate it from the air. Thc air passes through the water separator sub to 

the bit while the water accumulates and is ejected out weep holes into the annulus of the drill 

hole above the bit. As the water travels up the hole to the surface, it mixes with the cuttings and 

reduoes dust emisdons at the mouth of the hole. This means of water separation works well for 

larger (25.4 cm (10 m.)) diameter hob. However, due to the space reqlufwnents nemsary for 

the internal components of the device, its me on smaller diameter blasthola drills is not 

possible. 
Rectntly, a new design of water separating sub was devcloped in Australia, The technology of 

this sub's components differed from the previous designs, enabling water separation in a smaller 

(16.8 cm (6 518 in.)) diameter unit. Many smaller surface mining operations drill with smdler 

rotary drill rigs and could possibly bendit by using this device in their drilling operations. This 

unit was tested and evaluated far its ability to rduce dust emissions during production drilling at 

a surfacc coal mine. This paper addresses the new design for smaller diameter blasthole drills. 

2. Equipment 

21Drill mdrjEcations 

A model DM 50 E IngtrsolI Rand rotary drill, origidly equipped with a dry dust collector 

system for dust control, was modified to enable water injection into the bailing air. The 

mod5cations allowed the injection of a controlled and measurable quantity of water into the 

bailing air on thedrill, The water is introduced into the airstream at the drill masthead. The water 

mixes with the air as it travels down the drill string toward the bit. The mixture encounters the 

water separator unit before it reaches the bit and separation takcs place. The watw is expelled 

above the bit while air travels to the bit and flushes out the rock cuttings. As the air and cuttipgs 

move up the drill hole annuIus, the water expelled from the water separator unit mixes with the 

cuttings and agglomerates dust particIes while being carried to the surface. Upon reaching the 

surface, the dust particles have been subjected to enough moisture to prevent them from becoming 

kborne upon emng the hole. 

A 757 1 (200 gal.) high-pressure water tank was instalIed on the drill carriage to provide the , 

water.to the barling air (figure 2). The water suppIy for the tank was drawn from an, on-site pond 

by a tank truck and theg pumped into the wattr tank on the drill. An airline from the drill's air 

compressor to the tank enabled pressurization within the tank to force the watw to the drill stem. 

A hgh-pressure 19 mm (314 in.) water line was connected from the tank to an airline that 

connected to the rotary drive at the top of the drill stem. This he supplied the water from the 

tank, through the rotmy drive, to the drill string. To maintain control and monitoring of 

the amount of watw, controls consisting of a valve and fiowmeter were installed inside the 

operator's cab. 

-

Figure 2. Water tank location on dnIl rig. 
2.2 PAMPA stabiKizing sub 

The device tested was supplied by DTH Supplies (DTHSupplies Pty Lid, 45 Spinnaker Ridge 

Way, Belmont, NSW 2280, Austraha). This device, called the Dust Arresting Multi-Purpose 

Adapter, or DAMPA', is a proprietary-designed, self-contained mechanical sub that uses 

&ntrifugal force to separate water from air. The DAMPA is a multi-chambered 'device that 

separates the air and water suppliedto the drill stem before it enters the drill bit. The drill's cutting 

bit L screwed into the sub so that the separation takes place just before the bit, thus preventing 

water from reaching the bit. After separation, the water is ejected from three ports located 120' 

around the circumfermce of the sub.The smalldiameter unit is 12-7 cm (5 in.) in diameter by 

55.9 cm (22 in.) long, and is rated at 0.28 m3/s (600 dm).According to the manufacturer's 

spdcations, only 4%of the bdIing air is lost fromthe ports and 97% of the water is removed 

from the air. The amount of water required to suppress dust varies because of hole size, 

penetration rate, overburden rack and air volume. The manufacturer suggests setting water Aow 

to a rate necessary to eliminate visible dust from the borehole, For this mining operation, 3.0 11 

min (0.8 gpm) of water was adequatefor dust supprtssion.Figure 3 shows a schematic Mustratian 

of the DAMPA unit and its location on the drill stem. 

Water 

!&I 

Pcou 

"A" w4mrm k 

'8"'mi 

'C*M-A 

'D' -an 

'E" wlcurmyna 

T"0wa-MFigure 3.Schematic of DAMPA unit (left). DAMPA installed on drill (right), 

*T?I~arrideincludes a word that is orirs arsairred to be a proprietary ram or trade mark. IIS inclusion docs not imply it bas 

quid POI legal purpoam a non-proprietary or genwal aipnlPnance. nor i6 any otherjudscment implied concerning its legal 

Itatus. Unt of this instrumtnt do~snot imply wdorameni by NIOSH. 
3. Sampling methods 

3.1 DAMPA sub trials 

Field testing of the DAMPA sub was conducted at a and1 surface cod mine located in 

northern West Virginia. During these trials themDAMPAsub was tested to evaluate its 

effectiveness for reducing respirable silica dust. Two sampling methods were used to rnmsure 

respirable dust emissions while using the DAMPA sub. One method, which has ban described 

previously by Listak (2003), used a cascade cyclone (Model 283-2, Grasebe-Andersen,Smyma, 

GA)that sampled respirable dust inside the dust collector tube, This samplc was weighed and 

then sent to a laboratory to determine the silica content of the airborne dust sample. The other 

method uses an ME personal data ram @DR) (Model pDR 1200, Thmo Elecron Corp., 

Smyma,GA) placed adjacent to the drill deck to record respirable dust cone~ntrationsoutside 

the drill shroud.Figure 4 shows the locations of both systems. Thc sampling location of the 

cascade cyclone is sham to the kft of tbe drill deck next to the dust collector tube, The pDR 

sampler,used to record respirable dust concentrations outside the driIl shroud, was located in 

front of the drill deck for taeh test. Field testing was completed over four days of testing at the 

mine site. 

All the holes drilled and used for data analysis utilized three drill steels of 7,6m (25 ft) length. 

The third drill steel was only partially drilled as drilIing stopped when cod was encountered. The 

DAMPA was installed and used during both dry and wet drilling.During the drilling optrations s 

time study was performed, recording tbe start and stop times of the hole drilling, dong with the 

times required for adding additional drill steels. 

* 

Figure 4. hation of dust sampling instruments. 
3,2Cascade cyclone 

A component of the drill's dust coIIector system that draws a consistent amount of airborne dust 

from the hole is the collector tube,Assuming the coIlector system is working as designed, sampling 

from within the collcctor tube would enable a more consistent and better representative dust 

sample. Due to the large amounts of dust emitted during drillmg, the cascade cyclone was selected 

as a means of sampling because it has a high particulate coIIection capacity (up to 10 g per stage), 

which permits longer sampling times. It codd therefore be used for sampling in the collector tube 

for the entire length of the drill hole. 

The sampler consists of two cyclones with particulate collcctor cups and a backup Alter for three 

size classifrcatians.The cyclone measures the aerodynamic particle size instead of its physical size. 

The aerodynamic size or diameter is a measure of the inertial behaviour of the particle moving in 

air and is defined as the diameter of a unit density (1 dm') sphere that settles with the same 

velocity as the particle (Lodge and Chan 1986). Therefore, the aerodynamic dmneter gives 

information not only of the size but also of the density of a particle and indicateshow the particle 

will behave in an environment. When sampling at a flow rate of 28.3 l/min, the cascade cyclone 

sampler is designed to classify dust at aerodynamic diameters of 7.5, 2.7and 0,57 ps.The final 

stage (at 037 km)contains a 63 mm PVCfilter. Filters were pre- and post-weighed on a MettlerToledo microbalance (precision 5 pg) (Model UMT2, Mettler-Toledo, Columbus, 0E.I)in a 

climate-controlled room after desiccation md equilibration. 

In order for the cascade cydone to collcct respirable dust samples from insidethe dust collector 

tube during drilIing operations,a port was created in the dust collector tub to allow the nozzle 

inlet of the cycIone to bc inserted into the tube. Velocity measurements were talcen inside the 

collector tube to match the sampling velocity of the nozzle to the velocity ofair in the tube so that 

samples could be taken,isokineticalIy (Willeke and Baron 1993). Thc sampler has a range of 

interchangeable nozzles of varying diameters to allow for isokinttic sampling at velocities ranging 

from 8.0- 50.3 rn/s (1570- 9910 fpm). An initial velocity of 9.9 m/s (1950 fpm) was measured, 

which is a low speed for dust collection efficiency. After opening the collector and cleaning the 

flters, the velocity increased to 282 m/s (5550 fpm). 

The cyclone was set up adjacent to the dust callector tube and connected to a vacuum pump 

operating at a 28.3 l/min flow rate. The samples from the dust coflector tube were collected from 

the two sampling cups, with cut points of 7.5 +d 2.7 pm, and on the fdter mounted in the cyclone. 

After every hole, the cups were emptied and the filter was removed and stored to later determine 

dust concentration and silica content. After each hole, the cyclone setup was removed to dow the 

drill to tram to the next hole and then reassembled for sampling the next hole. 

3.3 Personal data ram (pDR} 

The pDR is a real-time monitoring instnunent for measuring mass concentrations of dust, mist, 

smoke and fumes, It was used in this study to measure the respirable fraction of airborne dust 

during rotary drilling. The pDR is a light-scattering nephelometer. The intensity of the light 

scattered over s forward angle of 50-90' by airborne particles passing through the sensing 

chamber of the device is linearly proportional to their concentration. Particle measurement is a 

function of the light reflected into the detector from the particles. This optical configuration 

produces optimal response to psrticlts in the size range of 0.1-10 pm. Thesc instantaneous 

sampling instruments provide relative differences in dust levels. The unit has a concentration. 

measurement range of 0,001-400 mg/m3. Time-stamped dust leveIs are stored at specified 

intervals in thc unit for subslqucnt download to a computer, For calibration purposes, a 
gravimetric sampler is used with the pDR during each dust sampling survey, and then the pDR 

is cdibrated against the gravimetric measurement to arrive at dust concentrations for the unit. 

The authors feel this is a more accurate way to sample with the pDR because it takes into 

consideration that the dust cloud may not be consistent from test to test or from survey to survey. 

Zeroing of the pDR units was performed aner every test according to the manufacturer's 

spec8cation using the zeroing bag, 

Using the pDR,real-time dust measurements were taken outside the shroud area in front ofthe 

drill every 5 s while dry drilfing was performed on four different holes to determine the amount of 

dust escaping the collecior system.The DAMPA was installed and measurements were taken on 

four holes while drilling with water. 

Surf- mine operations often face opposition from nearby communities for mating large 

amounts of dust that propagate into residentid areas.Most of this dust is createdfrom haul roads 

and drilling operations, and health concerns about the dust often arise. Obstrvations were thus 

made to determine thevisible differencein dust in the area around the drill when drilling with each 

method. The differenas in visible dust were documented through photographic pictures taken 

during testing. 

4.1 Cwcads cyclone 

The sampling plan ded for drilling and sampLing ten holcs using the dry collector and ten boles 

using the DAMPA. A total of 18 holes were monitorad for dust levels and visible dust dwing four 

days of testing. Various operational problems arose duriq tssting that prevented the colIection of 

complete data for a11 of the plannd test holes wbile using the DAMPA. These operationaI 

problems caused incondisttnt sn-mpling results because of the downtime during the drilling snd 

abandonment of holcs during the wet drilling process. Howtvtr, dust reductions were seen on 

every hole dnlled while drill~ngwith water. Although problem arose that did not allow complete 

sampling of the entire set of wet-drilled holes, data were collected for four complete holes while 

wet drilling with the DAMPA installed. Undw the assumption that thesc four holes are 

representative of all wetdnled holes, for comparative purposes, these four wet-drilled holes were 

compared to four holes that were smplcd while using only the dry coIlcctor. The four dry holes 

chosen for comparisonwere shih in depth and proximity to the four complete holes drilled with 

the DAMPA, tach using three drill steels and located on the same drill bench. Other dry holes 

were not used because they were not located near the holes that were drilled using the DAMPA. 

Samples taken from the cyclone (collector tube) were amlysed for dust mass and percent silica 

on the final Alter, Drilling time is the actual time thc bit was drilling and does not include the time 

to change drill see1 or remove the drill steel and tram to the next hole. Table 1 shows the data 

collected from thc eight holes, 

The most dramaticdifference between the two drillingmethods was the concentration measured 

in the collector tube by the cycione. An average reduction from 490.8-24.2 mg/xn3 was realized 

when using the wet drilling method (figure 5). 

The advance rate (penetration rate) for each method was also recorded during dry and wet 

drilling--0.64 rnlmin (2.I fwn) and 0.59 Wmin (1.9filmin), resptively. Advance rate vaned 

little, as did the amount of silica in the cyclone sampks, A bulk sample af the drill hole cuttings ' 
Table 1. Dust levels and silica amounts measured with the cascade cyclone. 

Hole Dtpth m (ft) DriIling time minutes Dwt concentration mg/m3 Silica % 

Dry 

1 I 8.9 (62) 29 313.3 - 30.3 

2 21.6 (71) 33 203.7 3 1.6 

3 20.4 (67) 33 711.2 25:O 

4 21.3(70) 32 734.8 25.4 

Avg 20.6 (67.5) 32 - 490.8 28.1 

Wet 

1 18.3 (60) 25 24.6 44.8 

2 17.4 (57) 21 23.7 22.4 

3 16.5 (54) 34 27.8 21.8 

4 16.8 (55) 39 20.7 16.8 

Ava 17.3 (56.5) 30 24.2 26.5 . 

Wet vs Dry Drilling 

Figure 5. Dust concentration in colIector tube when drilling dry versw .wet. 

was also collected and analysed for silica content to compare the amount of silica collected on 

the filter in the cyclone samples to the silica amount from the cuttings. The silica content in the 

cuttings taken from samples of four holes (one dry and three wet) was 59.3%, as opposed to an 

average of 27.3% from cyclone filter samples taken from the same holes. This result shows that 

' 	

the overall silica content of thc rock being drilled is more than twice the silica content of the 

fine-sized (>2.7 pn)airborne samples collected from the collector tube. This result wggesb that 

silica content ofthe rock cannot be used as a measure of the silica content in the respirable 

sample. This finding concurs with an underground study of host rock silica content (Ramani 

at al. 1987). 

4.2 Visual obser~arions 

From a visual perspective, thc area surrounding the ddl was much cleaner using the wet drilling 

method, Figure 6 shows drilling with both methods on the same bench and under the same 

conditions. Both pictures were taken when the drill was fully operational and drilling was 

undenvay. T3tse pictures art typica1,forall holw dqcd over the muse of the survey. 
4.3 Personal data rams 

To measure the dust escaping the dust collection system, instantaneousrespirable dust concentrations outside the drill shroud wcrc coIlected in addition to the dust within thc system.Area sampling 

of dust with these instruments outdoorscanbe di5tult because the dust concentrationsvary greatly 

depending on wind conditions (i,e,direction and speed). The pDRs wtrc used in this study to give 

the relative differencesin dust at thedrill deck durlngeachmethod ofdrilling.The pDR used inthis 

study was positioned in front of the drill deck for each ofthe tests, as shown in figure 4. 

The instantaneous data from the pDR are plotted in figure 7, which shows the average 

instantaneousrespirable dust concentrationsin mg/m3 for each hole drilled for both wet and dry 

drilling. These concentrations consist of the averages of all concentrations measured by the pDR 

for the total hole length (top to bottom for tach hole). Figure 7 shows that the respirable dust 

Figure 6,Dust liberated during dry drilling (left) and wet drilling (right). 

0 

1 2 3 4 

Drill Hole 

Figure 7. Comparison of dust concentratio~sin dry drilling versus wet drilling, 
concentrations ranged from 1.042-32.297 mg/ms for dry drilling, while the concentrationsranged 

from 0.217- 8,502 rng/m3 for wet drilling with the DAMPA sub, indicating that wet drilling 

effectively reduced respirable dust concentrations. It should be noted that the higher respirable 

dust concentration of 8.502 mdm3 from drill hole 4 of the wet drilling was due to the large 

shroud-to-ground gap of approximately 30.5-61 cm (12-24 in.). This occurred because of the 

ground surface sloping downhill away from the drill. Other shroud-to-ground pps for the othcr 

drift holes were not as significant, only varymg from 25.4-50.8 mm (1-2 in.). Ideally, the shroud 

should fit tightly to thc ground but because of ground undulations or grade changes, complete 

contact with the ground is rare. The other variations iq respirable dust concentrations might have 

been due to changing wind directions and wind speeds (throughout most of the day the wind was 

calm, with slight breezes occurring often and sometimesshifting directions). 

As the results described in this paper indicate, wet drilling reduces the amount of dust generated 

during drilling operations. The purpose of the DAMFA is to perform wet drilling while allowing 

the drill bit to work under conditions that are dose to dry drilling, thus endling longer bit Me. 

However, th~sstudy was not able to determineif there are any benefits to the drill bit life as a result 

of using the DAMPA. This was due to various problems encountered at the mine site, both 

operational and logistical. 

Many of the problem encountered when using theDAMPA were due to the regulation of water 

Aow. Sptcifically, constantwattr flow to the device was not maintained bust of the method of 

pressurization of the water tank. Water flow from the tank varied as water levels in the tank 

chmged during usage. A flowmeter and valve mounted in the cab did not provide enough control 

to properly regulate the pow to the unit. This problem could be solved by using a constant flow 

pump on the outaow of the tank, 

, The condition of the overburdm at this site also had a detrimental dect on drilling 

performance.Thc overburden being drilled was highly weatbered and fractured.Whtn flows were 

too high the high-pressure water ejecting from the weep holes of the DAMPA caused hole-walI 

deterioration and spalIing above the bit. This circumstancecaused the boles to cave in, requiring 

re-ddling without water and, in some cases, abandoning the entire bole. This d~dnot seem to 

occur when dry drilling with the DAMPA. 

There was a significant amount of troubleshaoting required to resolve these two conditions, 

which limited the amount of data obtained during the study. Additionally, the mine site was a very 

md operation where drilling did not occur on a consistentbasis. However, being smalldid a110.w 

the flexibility for successful troubleshooting to occur without interfering with other mine 

operations. Moreover, this mine rcIied upon a drilling contractor to perform the majority of its 

drilling needs. Therefore, while this site provided significant rcsourcea and produobd good quality 

dust measurement data, it was not ideal for determining long-term bit performance with the 

DAMPA. 

For the testing completed at this mine site, here is no indication that the DAMPA had 

any impact upon the silica content of the dust in the cyclone samples, although ths was an 

expected result. The silica content would vary significantly bastd upon the surroundinggeology, 

rather than whether or not water was wed in the drilling operation. Also, the amount of h e 

spent drilling (advance rate) to complete the drill holes was not significantly different with or 

without water when using the DAMPA. However, with the limited amount of data (eight 

dtill holes total), it is not possible to determine any impact upon the drilling rate with or without 

water. 
Surfatx mine blasthole drilling generates large amounts ofrespirable airborne dust. When drilling 

through overburden, there is a high potential for this dust to contain silica, which can cause 

silicosis in employees in the vicinity of the drilling operation. While dust colIactors we gmcrally 

used to reduce airborne respirable dust surrounding the drill, water is mother method that has 

been shown to be efTective at reducing dust levels. 

Tht evduation of the respirable dust 1eveIs of a rotary drill white driIling overburden 

blastholes with the DAMPA dry versus drilling with water showed that dust levels surrounding the drill could range anywhere fmm 1,042-52.297 mg/m3 when drilling dry versus 

0.217- 8.502 mg/ms when drilling wet. Dust measured in the drill's collector tube by the 

cyclone showed that dust levels were on average approximaely 20 times higher when drilling 

dry (490.8 mg/m3) versus drilling with water (24.2mg/m3). This shows that wet drilling with 

the DAMPA can roduce airborne rcspirkble dust levels generated during drilling operations, 

An added b&t of drilling with water is that the cuttings that are expelled and accumulate 

around'the holts arc wetted and heavy and are thus less likely to be entrained into the 

air during windy conditions. This benefit could possibly reduce thc reapirabIe dust Ievtls 

for the blasting preparation that occurs around the drilI pattern once d&ng has been 

completed. 

Silica amounts in the respirable dust samples ranged from 25.0-31.6% for dry drilling and 

16.8 -44.8% for wet mng. Thc silica content averages did not vary'significantly. It is expected 

that any variationsin silica contents were caused by the varying geology of the drill holes. Drilling 

times did not vary signihtly during testing whether dry drilling (32 minute average) or wet 

drilling (30minute average) with the DAMPA. The amount of data collded during this study, 

due to operational and lggistical probIemn, was not sufficient to determine the long-term effects of 

the DAMPA on ddl bit performance. 

In conclusion,wet drilling with the DAMPA sub did reducerespirabledust levels during drilling 

operations. Problems were encountered using the DMA, but thew were deemed to be 

correctable. Continued work and refinement of the proces n& to be completed in order to 

determine any effects on long-term drill bit ptrformmce wha wing the DAMPA to drill 

blastholes at surfam mining oprations. 

Acknowledgements 

We acknowledge David Hama of DTH Suppfics for his contributions to this study and for 

supplying the DAMPA unit for evaluation. 

ATSDR,Toxu~lo#dRq% forEthyltnt Gbcoland Pmpylma Qfycol. Agency for Toxic SubatanceaahDisease Registry, 

Atlanta, QA, 1997. 

ATSDR, TOXFAQ~~ Ebr Ethylem GIycaI md Propylene Giyoi.Agency for Toxic Substanas and Disease Rcgisuy, 

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