5
RESULTS AND DISCUSSION
DCAC Air Velocity Profile
Previous research on canopy air curtains showed that
velocities greater than 0.5 m/s are necessary for greater
than 50% reduction in dust concentration, but air veloci-
ties over 2.0 m/s may create worker discomfort (Listak and
Beck 2012, Roghanchi et al. 2016). Using these criteria, the
DCAC was designed to create flow rates from 0.5 to 2.0 m/
sec. Figure 6 is an air velocity profile measured at 15 inches
below the DCAC, as discussed in the Methods section. This
figure shows that, although the flow rate across the DCAC
is not uniform, it does generally meet the 0.5 to 2.0 m/s
specifications, as discussed in the Methods section.
DCAC Flow Rate
The air volume entering the DCAC system did not signifi-
cantly decrease during our testing. Over the 394 minutes
the DCAC was operating, the accumulation of DPM on
the MERV 16 filter resulted in a 4.8% reduction in air vol-
ume moving through the system. One concern with using
the DCAC was that the MERV 16 filter would quickly clog
with DPM and reduce the flow rate to the DCAC, result-
ing in reduced miner protection. Additional tests are neces-
sary for the optimization of filter type to both reduce DPM
exposure and filter replacement.
Reduction in DPM (as EC)
Table 1 presents the reduction in DPM (as EC) measured
under the direct center of the DCAC for each of the tests.
As shown in Table 1, measurements with the SKC
DPM cassette ranged between 84% and 89% with an
average of 87% and ranged between 80% and 85% with an
average of 83% using the Airtec monitors. Figure 7 pres-
ents a chart showing the averaged Airtec monitor data over
the three tests. As shown, the initial stabilization period
results in very similar DPM concentrations, with a signifi-
cant decrease once the DCAC is started. DPM exposure
for underground blasters have been recorded above 500
μg/m3. With the greater than 83% protection provided by
the DCAC, miners’ exposure would be reduced from 500
μg/m3 without the control to 85 μg/m3 using the DCAC,
which is below the MSHA permissible exposure limit
(PEL) for DPM.
Reduction in Particle Number Concentrations
Figure 8 presents a contour plot showing average particle
number reduction over the three tests using the NanoScan
across the operating DCAC, and Figure 9 presents a con-
tour plot showing average particle number reduction over
the three tests using the APS across the operating DCAC.
Figure 5. Photo of the DCAC inside the test entry
showing the sampling baskets, real-time instruments and
measurement grid
Figure 6. DCAC Air Velocity Profile measured 15 inches
below DCAC surface
Table 1. Percent reduction in DPM (as EC) measured under
the direct center of the DCAC.
Test Date
Percent DPM (as
EC) reduction
with DPM
cassettes
Percent DPM (as EC)
reduction with Airtec
monitor
8/10/2023 84 83
8/17/2023 88 80
8/22/2023 89 85
Average 87 83
Std dev 2.6 2.5
RESULTS AND DISCUSSION
DCAC Air Velocity Profile
Previous research on canopy air curtains showed that
velocities greater than 0.5 m/s are necessary for greater
than 50% reduction in dust concentration, but air veloci-
ties over 2.0 m/s may create worker discomfort (Listak and
Beck 2012, Roghanchi et al. 2016). Using these criteria, the
DCAC was designed to create flow rates from 0.5 to 2.0 m/
sec. Figure 6 is an air velocity profile measured at 15 inches
below the DCAC, as discussed in the Methods section. This
figure shows that, although the flow rate across the DCAC
is not uniform, it does generally meet the 0.5 to 2.0 m/s
specifications, as discussed in the Methods section.
DCAC Flow Rate
The air volume entering the DCAC system did not signifi-
cantly decrease during our testing. Over the 394 minutes
the DCAC was operating, the accumulation of DPM on
the MERV 16 filter resulted in a 4.8% reduction in air vol-
ume moving through the system. One concern with using
the DCAC was that the MERV 16 filter would quickly clog
with DPM and reduce the flow rate to the DCAC, result-
ing in reduced miner protection. Additional tests are neces-
sary for the optimization of filter type to both reduce DPM
exposure and filter replacement.
Reduction in DPM (as EC)
Table 1 presents the reduction in DPM (as EC) measured
under the direct center of the DCAC for each of the tests.
As shown in Table 1, measurements with the SKC
DPM cassette ranged between 84% and 89% with an
average of 87% and ranged between 80% and 85% with an
average of 83% using the Airtec monitors. Figure 7 pres-
ents a chart showing the averaged Airtec monitor data over
the three tests. As shown, the initial stabilization period
results in very similar DPM concentrations, with a signifi-
cant decrease once the DCAC is started. DPM exposure
for underground blasters have been recorded above 500
μg/m3. With the greater than 83% protection provided by
the DCAC, miners’ exposure would be reduced from 500
μg/m3 without the control to 85 μg/m3 using the DCAC,
which is below the MSHA permissible exposure limit
(PEL) for DPM.
Reduction in Particle Number Concentrations
Figure 8 presents a contour plot showing average particle
number reduction over the three tests using the NanoScan
across the operating DCAC, and Figure 9 presents a con-
tour plot showing average particle number reduction over
the three tests using the APS across the operating DCAC.
Figure 5. Photo of the DCAC inside the test entry
showing the sampling baskets, real-time instruments and
measurement grid
Figure 6. DCAC Air Velocity Profile measured 15 inches
below DCAC surface
Table 1. Percent reduction in DPM (as EC) measured under
the direct center of the DCAC.
Test Date
Percent DPM (as
EC) reduction
with DPM
cassettes
Percent DPM (as EC)
reduction with Airtec
monitor
8/10/2023 84 83
8/17/2023 88 80
8/22/2023 89 85
Average 87 83
Std dev 2.6 2.5