2
and then supplies clean air beneath the canopy where a
miner is working.
The use of the canopy air curtain to reduce exposures
to diesel particulate matter was first discussed by Noll et al.
(2020). In this study the diesel canopy air curtain (DCAC)
reduced the DPM concentrations under the canopy by
up to 90%. For this research the DCAC was designed to
attach to the basket cover of an ammonium nitrate fuel oil
(ANFO) loader (Figure 2) and provide clean air blowing
over the miners as they work in the basket. The initial tests
used clean air drawn from the mine’s intake and did not
try to filter the DPM from the air. Filtering DPM has extra
challenges when compared to filtering mine dust particles.
The particles of DPM are smaller (submicron and nanome-
ter) than dust particles (greater than 1 micron) therefore,
the filtration system must be adjusted to capture submicron
particles. A MERV 13 filter was used in previous canopy air
curtain research on mine dust control, but this filter is only
designed to capture 50%–75% of submicron particles, and
this capture efficiency is too low for removing DPM, so a
higher efficiency filter is needed.
Higher efficiency filters increase the pressure across
the filter media which results in decreased airflow or leaks
around the filter and reduces the effectiveness of the con-
trol for protecting miners from DPM. The optimal filter
needs to capture DPM particles at a high efficiency while
still allowing the needed airflows to prevent contaminated
air from entering the miner’s breathing zone. Listak and
Beck (2012) recommended velocities greater than 0.5 m/s
for dust reductions of greater than 50%. However, airflows
too high have been shown to reduce miners’ thermal com-
fort Roghanchi et al. (2016) suggest the optimal velocity
for thermal comfort is between 1–2 m/s. Thus, airflow over
the miner should be limited to the range of 0.5 to 2.0 m/s.
This current study presents the results from research
evaluating the reduction of DPM concentrations, under
the DCAC, when using a higher efficiency filter (MERV
16) to remove DPM from the DCAC airstream.
METHODS
DPM Laboratory in Experimental Mine
Evaluation of the DCAC occurred in the Experimental
Mine at the NIOSH Pittsburgh Mining Research
Laboratory. Figure 3 is a schematic of the diesel labora-
tory in the Experimental Mine. The test entry measures
approximately 13 feet across, 7 feet high, and 40 feet long.
Ventilation flow was maintained through the test entry
using a 4,000-cfm fan with the intake located at the back
of the test entry and being exhausted into the first cross-
cut for removal in the mine’s return. DPM was injected
into the test entry using a diesel generator—Onan model
number 12.5HDKCB-11506E with power output 12,500
watts max. @120/240 volts, 1 phase, 52 amps, 1800 rpm
Genset (3-cylinder in-line water cooled indirect injection
4-stroke, which meets 2012 Tier 4 emissions for U.S. EPA
and California nonroad CI engines (Cummings, Gibsonia,
PA). For all tests, the Genset load was set to 72% (9,000
watts). A mixing fan, located 6 feet directly in front of the
diesel exhaust pipe, is used to mix the fresh air and diesel
exhaust. DPM continuously fills the entry, and the ventila-
tion through the test section is approximately 30 ft/min,
flowing from the stopping to the face of the entry and then
out via the vent tubing into the first crosscut.
The DCAC (Noll 2020) was centrally located in the
test entry in the Experimental Mine as shown in Figure 3.
Briefly, each plenum, fabricated using durable flame-retar-
dant plastic, measured 3-ft by 3-ft (0.91-m by 0.91-m)
with a series of boreholes at uniform spacing (Figure 4) and
designed to create airflow of 1.16 m/sec at each borehole
Figure 1. Schematic of canopy air curtain
Figure 2. ANFO loader with basket (the DCAC would be
inserted over the basket)
and then supplies clean air beneath the canopy where a
miner is working.
The use of the canopy air curtain to reduce exposures
to diesel particulate matter was first discussed by Noll et al.
(2020). In this study the diesel canopy air curtain (DCAC)
reduced the DPM concentrations under the canopy by
up to 90%. For this research the DCAC was designed to
attach to the basket cover of an ammonium nitrate fuel oil
(ANFO) loader (Figure 2) and provide clean air blowing
over the miners as they work in the basket. The initial tests
used clean air drawn from the mine’s intake and did not
try to filter the DPM from the air. Filtering DPM has extra
challenges when compared to filtering mine dust particles.
The particles of DPM are smaller (submicron and nanome-
ter) than dust particles (greater than 1 micron) therefore,
the filtration system must be adjusted to capture submicron
particles. A MERV 13 filter was used in previous canopy air
curtain research on mine dust control, but this filter is only
designed to capture 50%–75% of submicron particles, and
this capture efficiency is too low for removing DPM, so a
higher efficiency filter is needed.
Higher efficiency filters increase the pressure across
the filter media which results in decreased airflow or leaks
around the filter and reduces the effectiveness of the con-
trol for protecting miners from DPM. The optimal filter
needs to capture DPM particles at a high efficiency while
still allowing the needed airflows to prevent contaminated
air from entering the miner’s breathing zone. Listak and
Beck (2012) recommended velocities greater than 0.5 m/s
for dust reductions of greater than 50%. However, airflows
too high have been shown to reduce miners’ thermal com-
fort Roghanchi et al. (2016) suggest the optimal velocity
for thermal comfort is between 1–2 m/s. Thus, airflow over
the miner should be limited to the range of 0.5 to 2.0 m/s.
This current study presents the results from research
evaluating the reduction of DPM concentrations, under
the DCAC, when using a higher efficiency filter (MERV
16) to remove DPM from the DCAC airstream.
METHODS
DPM Laboratory in Experimental Mine
Evaluation of the DCAC occurred in the Experimental
Mine at the NIOSH Pittsburgh Mining Research
Laboratory. Figure 3 is a schematic of the diesel labora-
tory in the Experimental Mine. The test entry measures
approximately 13 feet across, 7 feet high, and 40 feet long.
Ventilation flow was maintained through the test entry
using a 4,000-cfm fan with the intake located at the back
of the test entry and being exhausted into the first cross-
cut for removal in the mine’s return. DPM was injected
into the test entry using a diesel generator—Onan model
number 12.5HDKCB-11506E with power output 12,500
watts max. @120/240 volts, 1 phase, 52 amps, 1800 rpm
Genset (3-cylinder in-line water cooled indirect injection
4-stroke, which meets 2012 Tier 4 emissions for U.S. EPA
and California nonroad CI engines (Cummings, Gibsonia,
PA). For all tests, the Genset load was set to 72% (9,000
watts). A mixing fan, located 6 feet directly in front of the
diesel exhaust pipe, is used to mix the fresh air and diesel
exhaust. DPM continuously fills the entry, and the ventila-
tion through the test section is approximately 30 ft/min,
flowing from the stopping to the face of the entry and then
out via the vent tubing into the first crosscut.
The DCAC (Noll 2020) was centrally located in the
test entry in the Experimental Mine as shown in Figure 3.
Briefly, each plenum, fabricated using durable flame-retar-
dant plastic, measured 3-ft by 3-ft (0.91-m by 0.91-m)
with a series of boreholes at uniform spacing (Figure 4) and
designed to create airflow of 1.16 m/sec at each borehole
Figure 1. Schematic of canopy air curtain
Figure 2. ANFO loader with basket (the DCAC would be
inserted over the basket)