6
unaffected by the inserted gas. Out of the 5 sampling loca-
tions, tracer gas SF6 was detected only at the tailgate side
bleeder entry inby the face, the BEP, and the gob near the
22 gas insertion points on the tailgate side.
Figure 6 indicates the ability of the LIAM ventilation
system to dilute and render harmless breach gas from a
340-CFM gas inflow that enters the mine at the roof level
in 30 locations as shown in yellow (identified as 1 and 2).
No gas is detected on the longwall face. In this test sce-
nario, 0.7221% gas is detected at the Bleeder Evaluation
Point (BEP), and the 0.4284% detected in the bleeder
entries inby are within acceptable limits (1%) as identified
in approved mine ventilation plans.
For the test cases with 500-cfm and 1,300-cfm gas
inflow, the gas flow paths are very similar with what the
340-cfm case obtained illustrated in Figure 6, which flow
from the release locations to the tailgate side bleeder entry
toward the BEP. The longwall face remains unaffected by
released gas in the 500-cfm and 1,300-cfm case as well.
Table 2 shows the gas concentrations at selected sample
locations for all three test scenarios in the LIAM test. The
data indicate that gas concentration increases with the rise
in gas inflow. For example, at the BEP, the measured gas
concentrations are 0.72% for 340 cfm inflow, 0.87% for
500 cfm, and 1.10% for 1,300 cfm.
RESULTS FROM VENTSIM MODEL
Breached Gas Migration in the Mine
Various gas inflows ranging from 340 cfm to 1,500 cfm
from the breached gas were simulated in this longwall
layout with the same ventilation configuration. Figure 7
displays the breached gas migration in this study case for
the inflow of 340 cfm. According to the VentSim simula-
tion, once gas enters the ventilation system, a portion is
transported by the airflow to the bleeder entry and subse-
quently exits through the bleeder shaft. At the same time,
another fraction of the gas flows into the adjacent gob area.
Fortunately, the active face and its gob remain unaffected
by the breached gas. In the other simulation cases with
larger gas inflows, the same pattern was observed, although
the levels of gas concentrations were elevated.
Relationship Between Gas Inflow and Gas
Concentration at Some Key Locations
To evaluate the ventilation system’s capacity, NIOSH
researchers performed simulations with varying gas inflows
Figure 6. Sampled gas concentration at selected sampling locations for 340-cfm test case
unaffected by the inserted gas. Out of the 5 sampling loca-
tions, tracer gas SF6 was detected only at the tailgate side
bleeder entry inby the face, the BEP, and the gob near the
22 gas insertion points on the tailgate side.
Figure 6 indicates the ability of the LIAM ventilation
system to dilute and render harmless breach gas from a
340-CFM gas inflow that enters the mine at the roof level
in 30 locations as shown in yellow (identified as 1 and 2).
No gas is detected on the longwall face. In this test sce-
nario, 0.7221% gas is detected at the Bleeder Evaluation
Point (BEP), and the 0.4284% detected in the bleeder
entries inby are within acceptable limits (1%) as identified
in approved mine ventilation plans.
For the test cases with 500-cfm and 1,300-cfm gas
inflow, the gas flow paths are very similar with what the
340-cfm case obtained illustrated in Figure 6, which flow
from the release locations to the tailgate side bleeder entry
toward the BEP. The longwall face remains unaffected by
released gas in the 500-cfm and 1,300-cfm case as well.
Table 2 shows the gas concentrations at selected sample
locations for all three test scenarios in the LIAM test. The
data indicate that gas concentration increases with the rise
in gas inflow. For example, at the BEP, the measured gas
concentrations are 0.72% for 340 cfm inflow, 0.87% for
500 cfm, and 1.10% for 1,300 cfm.
RESULTS FROM VENTSIM MODEL
Breached Gas Migration in the Mine
Various gas inflows ranging from 340 cfm to 1,500 cfm
from the breached gas were simulated in this longwall
layout with the same ventilation configuration. Figure 7
displays the breached gas migration in this study case for
the inflow of 340 cfm. According to the VentSim simula-
tion, once gas enters the ventilation system, a portion is
transported by the airflow to the bleeder entry and subse-
quently exits through the bleeder shaft. At the same time,
another fraction of the gas flows into the adjacent gob area.
Fortunately, the active face and its gob remain unaffected
by the breached gas. In the other simulation cases with
larger gas inflows, the same pattern was observed, although
the levels of gas concentrations were elevated.
Relationship Between Gas Inflow and Gas
Concentration at Some Key Locations
To evaluate the ventilation system’s capacity, NIOSH
researchers performed simulations with varying gas inflows
Figure 6. Sampled gas concentration at selected sampling locations for 340-cfm test case