st no maintenance, is small and inexpen-
sive, and it will help operators maintain compliance to the dust
standard. The thought process was that a reduction of res-
pirable dust at any of the multiple sources on the drill, in this
case the dust collector dump point, should reduce the total res-
pirable dust generated by the drill.
The U.S. Mine Safety & Health Administration (MSHA) has a
coal respirable dust standard of 2 milligrams per cubic meter
(mg/m
3
) for an 8-hour shift. MSHA and mine operators period-
ically collect personal dust samples to determine compliance
with this dust standard.
Drill operators have one of the highest exposure levels to res-
pirable dust. This has been proven through many reviews of the
MSHA dust sampling database. Prior to 1987, the highwall driller
at surface coal mines had the most severe exposure to respirable
silica dust, a trend that continues today based on MSHA's res-
pirable dust sampling database.
A review of the MSHA database for the years 1985 through 1992
shows that 81% of the respirable silica dust samples taken exceed-
ed the permissible exposure limit for the highwall drill operator at
surface coal mines. A more recent review of the MSHA database,
for the years 1996 through 2000, shows that only 31% of the res-
pirable silica dust samples taken exceeded the respirable silica
dust limit for the highwall driller at surface coal mines. This sug-
gests a substantial improvement in preventing the exposure of
silica dust to the highwall drill operator. The drill operator, how-
ever, still tops the list of job occupations that have the highest
exposure to respirable silica dust.
Respirable dust has been shown to be harmful to human health,
especially when silica is present in the dust. It causes a disease
known as silicosis, which can occur in three levels: chronic silicosis,
which occurs after 10 years of exposure; accelerated silicosis, which
occurs between 5 and 10 years of exposure; and acute silicosis,
which can occur within a few weeks to five years of very high expo-
sure to silica dust. Respirable dust consists of the dust particle size
fraction whose median diameter is 4 micrometers (µm).
The drilling machine generates high concentrations of respirable
dust from several sources: drill table shroud leakage, dust leakage
through the table bushing, dust discharge from the dust collector
exhaust due to impaired filters, and dust entrained from the dust
collector fines dumped onto the bench. The National Institute for
Occupational Safety and Health's (NIOSH) Pittsburgh Research
Lab (PRL) has been studying different methods to reduce res-
pirable dust from these sources. During its testing, the institute
identified a simple solution that reduces the amount of respirable
dust generated at the collector dump point.
New Approach Controls Dust
at the Collector Dump Point
NIOSH Finds a Simple, Cost-Effective Solution for Reducing Dust for Blasthole Dills
Dust (including the respirable size fraction) becomes entrained in the atmosphere
from the dumping of fine material from the drill dust collector.
Schematic diagram of dust collector. Large arrows represent airflow.
By Wm. Randolph Randy Reed, John A. Organiscak, and Steven J. Page
CA_pg20-22.qxd 6/10/05 10:35 AM Page 20 THE PROBLEM: DUST COLLECTOR FINES DUMP
The drill's dust collector dumps fine material onto the bench and
generates respirable dust. The device collects dry dust from the
space below the drill table that is enclosed by the shroud. This area
contains respirable dust from the fine material removed from the
drill hole by the bailing air. This respirable dust frequently contains
high silica content.
A high-speed fan is used to pull dust-laden air from underneath
the drill table into the collector. This air is then routed through
filters to remove the dust particles and clean air is discharged
through the fan. The removed dust particles are captured on the
filters. The collector then uses a high-pressure pulse jet of air to
backflush the filters, removing the material off the filters at regu-
lar intervals. The backflushing occurs several times per minute.
The backflushed material drops from the bottom of the collector
onto the ground beside the drill machine.
The dust collector dump point rests anywhere from 24 to 36 inch-
es above the bench. Dumping the fine material from this height
causes entrainment of the respirable size fraction of this material
into the air. Recently, the average respirable dust concentration
measured at the dump location at a surface coal mine in
Kentucky varied from approximately 0.53 to 1.34 mg/m
3
, in time
periods ranging from 2.9 to 5 hours. These concentrations are an
average of three dust measurements taken with one personal-
data-ram gravimetric and two gravimetric filters all using 10-mm
Dorr-Oliver cyclones.
The measurements were taken within a distance of 2 to 3 ft
from the dust collector dump point. The prevailing wind
directions were used to determine the placement of the sam-
pling equipment with the samplers being placed downwind of
the dump point. Once the location was set with respect to the
drill, it was kept constant throughout the day of testing.
However, the sampling location did move with the drill to
maintain the 2 to 3 ft distance from the dump point.
THE SOLUTION: BRATTICE INSTALLATION
To reduce the respirable dust concentrations at the collector dump
point, a piece of brattice cloth was attached to the dust collector dump
point using a large hose clamp. This dust shroud is installed over the
existing rubber boot attached to the dust collector dump point.
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 out-
side 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 con-
taining the entrained respirable fraction within its confines.
Location of sampling equipment with respect to dust collector dump point.
Comparison of dust concentrations of uncontrolled dust collector dump to shrouded dust collector dump.
CA_pg20-22.qxd 6/10/05 10:35 AM Page 21 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 simple procedure of creating a dust collector dump shroud is
very effective in reducing the respirable dust. Respirable dust con-
centrations measured after installation of the dust collector
shroud ranged from 0.16 to 0.24 mg/m
3
. It can be seen that the
reduction of respirable dust generated by the dust collector dump
point can be reduced by between 63% and 88%. This reduction is
highly dependent upon wind direction and wind speed.
Advantages to 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 10-15
minutes requiring little, if any, downtime for the drill.
Author Information: Reed is a mining engineer for NIOSH-PRL
and can be reached at 412-386-5205 (or E-mail: Rreed@cdc.gov),
located near Pittsburgh. Organiscak is also a mining engineer for
NIOSH and Page is a research physicist for NIOSH-PRL.
References:
Croom, M.L.; Filter Dust Collectors, Design and Application. (New
York: McGraw-Hill, Inc., 1995).
Hale, J.; NIOSH's Division of Respiratory Disease Studies informa-
tional analysis of MSHA's dust sampling database, (2002).
Hinds, William C.; Aerosol Technology, Properties, Behavior, and
Measurement of Airborne Particles, 2nd Edition. (New York: John
Wiley & Sons, 1999).
International Standards Organization (ISO); Air Quality-Particle Size
Fraction Definitions for Health-Related Sampling. Draft Int. Standards
ISO Technical Report, ISO/TR 7708-1983 (E), (Geneva: ISO, 1993).
Lippmann, Morton; "Chapter 5 Size-Selective Health Hazard
Sampling." Air Sampling Instruments for Evaluation of
Atmospheric Contaminants, 8th Edition. American Conference of
Governmental Industrial Hygienists, ed. Cohen, Beverly S., and
Hering, Susanne V., (Cinncinati, Ohio: ACGIH, 1995) 81-119.
Maksimovic, S.D., and Page, S.J.; "Quartz Dust Sources During
Overburden Drilling at Surface Coal Mines." United States Bureau of
Mines Information Circular. 9056. (U. S. Department of Interior, 1985).
Metroplex Products, Inc.; M.P.I. Cutting Management Systems,
Blasthole Drilling, MPI-335 Application, Operation, and
Maintenance Manual for "Cutting Removal Systems," "Dust
Collector Systems". (St. Louis, MO: Metroplex Products, Inc., 1981).
Page, Steven J., and Maksimovic, Slavoljub D. "Transport of Respirable
Dust from Overburden Drilling at Surface Coal Mines." Proceedings of
the 3rd Mine Ventilation Symposium. Mutmansky, Jan M. ed.
(Littleton, CO: Society of Mining Engineers, Inc., October 1987) 625-629.
Soderholm, S.C.; "Proposed International Conventions for Particle
Size-Selective Sampling." Annals of Occupational Hygiene. Vol. 33,
No. 3., (1989) 301-320.
Tomb, T.F.; Gero, A.J.; and Kogut, J.; "Analysis of Quartz Exposure
Data Obtained from Underground and Surface Coal Mining
Operations." Applied Occupational Environmental Hygiene. Vol.
10, No. 1