5
significant leakage of nitrogen through the door gaskets was
measured. To overcome the problem, for the 2nd cham-
ber, the position of the doors was modified to open the
doors into of the chamber (inwards) when the doors are
open, and close them against the door frames (outwards)
when the doors are closed. Following this change, the
chamber was able to withstand pressure differentials in the
range of 1250 to 1500 Pa (5.0 to 6.0 in wg) without any
significant leakage.
Tests on the 1st Chamber
The results of two tests performed on the 1st chamber are
presented in this section: (1) to show the effect of baro-
metric pressure on pressure differential across the chamber
walls, and (2) to shows the effect of pressurized nitrogen
on the chamber walls. In each case, the chamber was filled
with pressurized nitrogen, the pressure differentials moni-
tored, and the chamber walls evaluated for their ability to
reduce the flow of oxygen into the gob, thus reducing the
risk of starting a fire. The results of the two tests are pre-
sented below.
Test 1—The Effect of Atmospheric Pressure on the
Chamber Pressure
This test was performed to determine the effect of
changes in atmospheric pressure on the pressure differen-
tials across the chamber’s stopping and seal. Figure 5 shows
four-time series data for a month (September 1–30, 2021):
one for surface air temperature, one for barometric pressure
and two for pressure differentials across the chamber’s stop-
ping and seal. Temperature and barometric pressure data
(brown and green lines) were recorded by digital sensors
located at the mine’s main office (on surface). The pressure
differentials (DP) were monitored by two digital manom-
eters: one used to measure pressure differentials between
the gob and the chamber (Seal DP or P3–P2 in Figure 4),
and another between the chamber and the entry (Stopping
DP or P2–P1). In Figure 5, the orange line represents the
pressure differentials across the seal (P3–P2), and the blue
line the pressure changes across the stopping (P2–P1). A
quick evaluation of these graphs shows that the barometric
pressure and temperature are inversely related and vary on a
daily basis. These variations affect both pressure differentials
across the chamber walls. For example, on September 22, as
shown in Figure 5, the barometric pressure varied between
a maximum of 30.6 in–mercury (Hg) at about 5 AM and
a minimum of 30.3 in–Hg at 4 PM (a total decrease of
0.3 in Hg or 4.1 in wg). During the same period, while
the pressure differentials across the seal varied significantly
(between +0.6 in wg and –1.4 in wg), the pressure differen-
tials across the stopping remained practically constant with
a mean of –0.1 in wg). These results showed that while the
permanent seal is robust and has the ability to hold high–
pressure differentials, the Kennedy stopping is not strong
enough to hold pressurized gas. Another finding is that the
pressure differentials across the permanent seal are directly
related to changes in barometric pressure i.e., when the
barometric pressure on the surface increases the pressure
differential across the seal (P3–P2) also increases to even
become positive (P3–P20), causing an out–gassing condi-
tion (green highlighted area in Figure 5). On the contrary,
when the barometric pressure on the surface decreases, the
differential pressure across the seal (P3–P20) becomes
negative, creating an in–gassing condition.
Test 2—The Effect of Nitrogen Injection on the
Pressure Chamber
This test was performed to determine the ability of the
chamber to hold pressurized nitrogen. Following a site
inspection and having found the chamber to be in good
conditions, the personnel doors were closed and locked, the
nitrogen flow control valves opened, and the chamber tested
Figure 4. Schematic of a pressurized nitrogen injection system
significant leakage of nitrogen through the door gaskets was
measured. To overcome the problem, for the 2nd cham-
ber, the position of the doors was modified to open the
doors into of the chamber (inwards) when the doors are
open, and close them against the door frames (outwards)
when the doors are closed. Following this change, the
chamber was able to withstand pressure differentials in the
range of 1250 to 1500 Pa (5.0 to 6.0 in wg) without any
significant leakage.
Tests on the 1st Chamber
The results of two tests performed on the 1st chamber are
presented in this section: (1) to show the effect of baro-
metric pressure on pressure differential across the chamber
walls, and (2) to shows the effect of pressurized nitrogen
on the chamber walls. In each case, the chamber was filled
with pressurized nitrogen, the pressure differentials moni-
tored, and the chamber walls evaluated for their ability to
reduce the flow of oxygen into the gob, thus reducing the
risk of starting a fire. The results of the two tests are pre-
sented below.
Test 1—The Effect of Atmospheric Pressure on the
Chamber Pressure
This test was performed to determine the effect of
changes in atmospheric pressure on the pressure differen-
tials across the chamber’s stopping and seal. Figure 5 shows
four-time series data for a month (September 1–30, 2021):
one for surface air temperature, one for barometric pressure
and two for pressure differentials across the chamber’s stop-
ping and seal. Temperature and barometric pressure data
(brown and green lines) were recorded by digital sensors
located at the mine’s main office (on surface). The pressure
differentials (DP) were monitored by two digital manom-
eters: one used to measure pressure differentials between
the gob and the chamber (Seal DP or P3–P2 in Figure 4),
and another between the chamber and the entry (Stopping
DP or P2–P1). In Figure 5, the orange line represents the
pressure differentials across the seal (P3–P2), and the blue
line the pressure changes across the stopping (P2–P1). A
quick evaluation of these graphs shows that the barometric
pressure and temperature are inversely related and vary on a
daily basis. These variations affect both pressure differentials
across the chamber walls. For example, on September 22, as
shown in Figure 5, the barometric pressure varied between
a maximum of 30.6 in–mercury (Hg) at about 5 AM and
a minimum of 30.3 in–Hg at 4 PM (a total decrease of
0.3 in Hg or 4.1 in wg). During the same period, while
the pressure differentials across the seal varied significantly
(between +0.6 in wg and –1.4 in wg), the pressure differen-
tials across the stopping remained practically constant with
a mean of –0.1 in wg). These results showed that while the
permanent seal is robust and has the ability to hold high–
pressure differentials, the Kennedy stopping is not strong
enough to hold pressurized gas. Another finding is that the
pressure differentials across the permanent seal are directly
related to changes in barometric pressure i.e., when the
barometric pressure on the surface increases the pressure
differential across the seal (P3–P2) also increases to even
become positive (P3–P20), causing an out–gassing condi-
tion (green highlighted area in Figure 5). On the contrary,
when the barometric pressure on the surface decreases, the
differential pressure across the seal (P3–P20) becomes
negative, creating an in–gassing condition.
Test 2—The Effect of Nitrogen Injection on the
Pressure Chamber
This test was performed to determine the ability of the
chamber to hold pressurized nitrogen. Following a site
inspection and having found the chamber to be in good
conditions, the personnel doors were closed and locked, the
nitrogen flow control valves opened, and the chamber tested
Figure 4. Schematic of a pressurized nitrogen injection system