6
for different gas flow rates. The test started on December 2,
2021, at approximately 9:07 AM. The control valves V1
and V2 (Figure 4) were opened, and the regulator R1
adjected so that the pressure gages G1 and G2 displayed
6 psi and 2 psi respectively (gas flow rate of about 20 cfm).
For the same flow rate, the test continued for several hours.
During this period, the barometric pressure and pressure
differentials across the chamber walls were monitored con-
tinuously, and the stopping was checked for leakage of
nitrogen or decrease in oxygen level frequently. The test
was immediately stopped when the oxygen concentration
in the access cross cut, outby the stopping, dropped to less
than 19.5%.
Figure 6 shows three time series for two days: one for
barometric pressure and two for pressure differentials across
the chamber walls. During the test period (highlighted area
in Figure 6), while the barometric pressure did not show
any significant change from its natural trend, the differ-
ential pressure across the seal decreased with the nitrogen
pressure. When the gas flow regulator was opened, the
pressure differential (P3 – P2) dropped from –0.4 in wg
(almost neutral) to –3.48 in wg (in–gassing), yielding a
combined pressure change of ∆P =–3.08 in wg. During the
time period highlighted in Figure 6, the DP across the stop-
ping fluctuated between –0.40 and +0.35 in wg. Figure 6
also shows that, during this period, the barometer readings
dropped from 30.42 in. Hg to 30.24 in. Hg. This represents
a decrease of –0.18 in. Hg., or –2.45 in wg. Consequently,
it is appropriate to assert that the decrease in differential
pressure across the seal is the result of a combined influence
of a decrease in barometric pressure underground coupled
with pressure loss in the chamber.
The above results showed that while the permanent seal
is robust and durable, the Kennedy stopping still requires
some additional reinforcement work. To overcome the
problem, the stopping was reinforced and sealant foam was
applied from both sides and tested again. This has improved
the ability of the stopping to hold pressure differential up
to 750 Pa (3 in. w.g). At this point, it was noticed that the
main leakage of nitrogen was through the coal fissures and
cracks around the stopping.
Tests on the Second Chamber
The results of two tests performed on the 2nd chamber
are presented in this section: (1) when the personal doors
were insatalled to open toward the fresh air side (outwards),
and (2) when the doors were installed to open toward the
chamber (inwards). The first test was conducted between
August 9 and 10, 2022, and the second on June 7, 2023.
In each case, hand-held TSI-micromanometers and ACR
Smart-Reader barometers were used to collect the data. The
results of these tests are presented below.
Figure 5. Effect of barometric pressure on chamber walls (seal and stopping)
for different gas flow rates. The test started on December 2,
2021, at approximately 9:07 AM. The control valves V1
and V2 (Figure 4) were opened, and the regulator R1
adjected so that the pressure gages G1 and G2 displayed
6 psi and 2 psi respectively (gas flow rate of about 20 cfm).
For the same flow rate, the test continued for several hours.
During this period, the barometric pressure and pressure
differentials across the chamber walls were monitored con-
tinuously, and the stopping was checked for leakage of
nitrogen or decrease in oxygen level frequently. The test
was immediately stopped when the oxygen concentration
in the access cross cut, outby the stopping, dropped to less
than 19.5%.
Figure 6 shows three time series for two days: one for
barometric pressure and two for pressure differentials across
the chamber walls. During the test period (highlighted area
in Figure 6), while the barometric pressure did not show
any significant change from its natural trend, the differ-
ential pressure across the seal decreased with the nitrogen
pressure. When the gas flow regulator was opened, the
pressure differential (P3 – P2) dropped from –0.4 in wg
(almost neutral) to –3.48 in wg (in–gassing), yielding a
combined pressure change of ∆P =–3.08 in wg. During the
time period highlighted in Figure 6, the DP across the stop-
ping fluctuated between –0.40 and +0.35 in wg. Figure 6
also shows that, during this period, the barometer readings
dropped from 30.42 in. Hg to 30.24 in. Hg. This represents
a decrease of –0.18 in. Hg., or –2.45 in wg. Consequently,
it is appropriate to assert that the decrease in differential
pressure across the seal is the result of a combined influence
of a decrease in barometric pressure underground coupled
with pressure loss in the chamber.
The above results showed that while the permanent seal
is robust and durable, the Kennedy stopping still requires
some additional reinforcement work. To overcome the
problem, the stopping was reinforced and sealant foam was
applied from both sides and tested again. This has improved
the ability of the stopping to hold pressure differential up
to 750 Pa (3 in. w.g). At this point, it was noticed that the
main leakage of nitrogen was through the coal fissures and
cracks around the stopping.
Tests on the Second Chamber
The results of two tests performed on the 2nd chamber
are presented in this section: (1) when the personal doors
were insatalled to open toward the fresh air side (outwards),
and (2) when the doors were installed to open toward the
chamber (inwards). The first test was conducted between
August 9 and 10, 2022, and the second on June 7, 2023.
In each case, hand-held TSI-micromanometers and ACR
Smart-Reader barometers were used to collect the data. The
results of these tests are presented below.
Figure 5. Effect of barometric pressure on chamber walls (seal and stopping)