2
In 2016, the University of Utah completed a research
project on “Control of Spontaneous Combustion Using
Pressure Balancing Techniques.” A physical model to mimic
a coal mine ventilation system was constructed as part of
this project. The model included a simulated mine gob, a
CO2-based pressure chamber, and a ventilation monitor-
ing system. The model was used to conduct several pressure
balancing tests. The results of these tests showed that pres-
sure balancing can be used effectively for control of sponta-
neous combustion conditions in
U.S. coal mines (Calizaya et al. 2016). Upon the con-
clusion of the project, a recommendation was given: “to test
the operation principles of a pressure balancing system in
the field.” This study summarizes the result of a follow-up
project to test the principles of pressure balancing to reduce
the risk of starting a Sponcom fire in a coal mine.
SELECTING A COAL MINE
Testing pressure balancing chambers in the field required
an underground coal mine where pressure chambers can be
constructed, tested and evaluated. Several coal mine opera-
tors were contacted to test this technique in their mines.
The coal mine located in Midwest Colorado was interested
in participating in this project. In this mine, the coal seam
is fairly flat, of about 3 m (10 ft) thick at about 150 m
(500 ft) below surface. The mine operates one longwall and
up to three development sections. The longwall panel uses
a common three-entry gate roads. The mine is ventilated
by a blower-type ventilation system equipped with two
surface fans. The combined capacity of these fans is nearly
600 m3/s (1,270 kcfm) at 2.50 kPa (10 in wg) of total pres-
sure. The longwall panel is ventilated by a bleederless ven-
tilation system where the mined-out areas are isolated by
means of high-pressure seals and the gob is inertized with
nitrogen gas that is injected from two to five cross-cuts inby
to the face from the headgate side.
Ventilation and atmospheric conditions at the mine
are monitored using a mine-wide Atmospheric Monitoring
System (AMS). The system includes different types of trans-
ducers to monitor both ventilation parameters (barometric
pressure, temperature, and air velocity), and mine gases
(O2, CO, and CH4). The barometers used at the mine are
set to display standardized (adjusted to sea level) barometric
pressures.
CONSTRUCTION OF TWO PRESSURE
CHAMBERS
Two pressure chambers were constructed at the ABC coal
mine: one in a mined-out area (1st Chamber), and the other
one in the active area (2nd Chamber), near a longwall mine
gob. Each chamber was established by installing a Kennedy
stopping in competent ground at about 3 m (10 ft) in front
of an MSHA-approved 800-kPa (120-psi) pressure seal. To
satisfy the MSHA requirements, the stopping design was
modified to include two personal access doors to allow the
mine personnel to inspect the seal weekly. Furthermore,
to reduce leakage, the Kennedy stoppings and access door
frames were sealed from both sides. Each chamber was
equipped with ventilation curtains to naturally ventilate the
chamber, a nitrogen injection system, pressure tubes, and a
set of ventilation and environmental monitors.
Because the project involved the utilization of pressur-
ized nitrogen and modifications to the current stopping
construction practices, a conceptual design for the chamber
was developed and submitted to MSHA. This was approved
before the construction work begun. In its salient features,
the design included:
a. Technical drawings of the chamber. The design speci-
fied the type of stopping to be constructed, type and
size of man-doors, details of the nitrogen injection
system, and the location of gas and pressure sampling
points.
b. Communication system. The design specified the
location of phone stations and warning signs near
the test area. These were linked to the mine’s com-
munication system to provide the mine operator
with the necessary information before, during, and
after the test.
c. Location of ventilation monitors and control devices.
In addition to the mine’s atmospheric monitoring
system, each chamber was equipped with oxygen
sensors located upwind and downwind of the cham-
ber with their alarm levels set at 19.5% O2.
d. Ventilation. A minimum air volume of 1.0 m3/s
(2,000 cfm) was provided at the chamber to allow
enough air to dilute the contaminates from leakage.
e. Nitrogen injection system. The design specified the
location of the nitrogen source, and size and length
of pipelines. All flow control valves, gages and regula-
tors were also specified.
f. Procedure to operate the chamber. This included
steps to operate a pressure chamber, process the data
and to determine the effect of pressure changes on
the flow of air.
Figure 1 shows a plan view of the drawing used for
the construction of the first chamber. It specifies the type
of stopping to be installed, type and size of man-doors,
details of the nitrogen injection system, location of gas sam-
pling points and pressure taps, and the location of gas and
In 2016, the University of Utah completed a research
project on “Control of Spontaneous Combustion Using
Pressure Balancing Techniques.” A physical model to mimic
a coal mine ventilation system was constructed as part of
this project. The model included a simulated mine gob, a
CO2-based pressure chamber, and a ventilation monitor-
ing system. The model was used to conduct several pressure
balancing tests. The results of these tests showed that pres-
sure balancing can be used effectively for control of sponta-
neous combustion conditions in
U.S. coal mines (Calizaya et al. 2016). Upon the con-
clusion of the project, a recommendation was given: “to test
the operation principles of a pressure balancing system in
the field.” This study summarizes the result of a follow-up
project to test the principles of pressure balancing to reduce
the risk of starting a Sponcom fire in a coal mine.
SELECTING A COAL MINE
Testing pressure balancing chambers in the field required
an underground coal mine where pressure chambers can be
constructed, tested and evaluated. Several coal mine opera-
tors were contacted to test this technique in their mines.
The coal mine located in Midwest Colorado was interested
in participating in this project. In this mine, the coal seam
is fairly flat, of about 3 m (10 ft) thick at about 150 m
(500 ft) below surface. The mine operates one longwall and
up to three development sections. The longwall panel uses
a common three-entry gate roads. The mine is ventilated
by a blower-type ventilation system equipped with two
surface fans. The combined capacity of these fans is nearly
600 m3/s (1,270 kcfm) at 2.50 kPa (10 in wg) of total pres-
sure. The longwall panel is ventilated by a bleederless ven-
tilation system where the mined-out areas are isolated by
means of high-pressure seals and the gob is inertized with
nitrogen gas that is injected from two to five cross-cuts inby
to the face from the headgate side.
Ventilation and atmospheric conditions at the mine
are monitored using a mine-wide Atmospheric Monitoring
System (AMS). The system includes different types of trans-
ducers to monitor both ventilation parameters (barometric
pressure, temperature, and air velocity), and mine gases
(O2, CO, and CH4). The barometers used at the mine are
set to display standardized (adjusted to sea level) barometric
pressures.
CONSTRUCTION OF TWO PRESSURE
CHAMBERS
Two pressure chambers were constructed at the ABC coal
mine: one in a mined-out area (1st Chamber), and the other
one in the active area (2nd Chamber), near a longwall mine
gob. Each chamber was established by installing a Kennedy
stopping in competent ground at about 3 m (10 ft) in front
of an MSHA-approved 800-kPa (120-psi) pressure seal. To
satisfy the MSHA requirements, the stopping design was
modified to include two personal access doors to allow the
mine personnel to inspect the seal weekly. Furthermore,
to reduce leakage, the Kennedy stoppings and access door
frames were sealed from both sides. Each chamber was
equipped with ventilation curtains to naturally ventilate the
chamber, a nitrogen injection system, pressure tubes, and a
set of ventilation and environmental monitors.
Because the project involved the utilization of pressur-
ized nitrogen and modifications to the current stopping
construction practices, a conceptual design for the chamber
was developed and submitted to MSHA. This was approved
before the construction work begun. In its salient features,
the design included:
a. Technical drawings of the chamber. The design speci-
fied the type of stopping to be constructed, type and
size of man-doors, details of the nitrogen injection
system, and the location of gas and pressure sampling
points.
b. Communication system. The design specified the
location of phone stations and warning signs near
the test area. These were linked to the mine’s com-
munication system to provide the mine operator
with the necessary information before, during, and
after the test.
c. Location of ventilation monitors and control devices.
In addition to the mine’s atmospheric monitoring
system, each chamber was equipped with oxygen
sensors located upwind and downwind of the cham-
ber with their alarm levels set at 19.5% O2.
d. Ventilation. A minimum air volume of 1.0 m3/s
(2,000 cfm) was provided at the chamber to allow
enough air to dilute the contaminates from leakage.
e. Nitrogen injection system. The design specified the
location of the nitrogen source, and size and length
of pipelines. All flow control valves, gages and regula-
tors were also specified.
f. Procedure to operate the chamber. This included
steps to operate a pressure chamber, process the data
and to determine the effect of pressure changes on
the flow of air.
Figure 1 shows a plan view of the drawing used for
the construction of the first chamber. It specifies the type
of stopping to be installed, type and size of man-doors,
details of the nitrogen injection system, location of gas sam-
pling points and pressure taps, and the location of gas and