COAL MINE INERTISATION BY REMOTE APPLICATION

By 

T. P. Mucho 

Thomas P. Mucho & Associates, Inc. 

Washington, PA 

I. R. Houlison

Phoenix First Response 

Glassport, PA 

A. C. Smith, and M. A. Trevits

NIOSH, Pittsburgh Research Laboratory 

Pittsburgh, PA
1 

COAL MINE INERTISATION BY REMOTE APPLICATION

T. P. Mucho 

Thomas P. Mucho & Associates, Inc. 

Washington, PA 

I. R. Houlison

Phoenix First Response 

Glassport, PA 

A. C. Smith, and M. A. Trevits

NIOSH, Pittsburgh Research Laboratory 

Pittsburgh, PA

ABSTRACT 

Timely and rapid intervention to underground combustion events (fires, explosions, and spontaneous combustion) is 

the key to the successful control of the mine atmosphere and restoring of a coal mine to production. The focus of 

this paper is the utilization of a GAG 3A jet engine system to combat either large out-of-control fires or to render an 

entire mine inert when access to problem areas is difficult or impossible. This system is based upon a Soviet 

designed agricultural jet engine which consumes aviation fuel with oxygen (O2) from the intake air and exhausts 

combustion gases, primarily carbon dioxide (CO2) and water (H2O), along with the nitrogen (N2) from the air and 

small amounts of carbon monoxide (CO) and hydrogen (H2). The system is designed to approach stoichiometric 

combustion (ideally, pure burning that scavenges all the oxygen from the intake air). Therefore, these exhaust gases 

are almost entirely “inert gases”- i.e., gases which do not contribute to, and in fact, can suppress the combustion 

process due to the lack of oxygen. Other methods to inert mine areas have been used in the US and internationally, 

but these methods usually use low flow inertisation equipment or methods. Use of these low-flow inertisation 

equipment and methods has been successful in proactively rendering gob areas inert and has the ability to inert the 

entire mine workings. Due to the low flow rate, however, a substantial period of time is required. Two events 

where the GAG-3A system was used in the United States (U.S.) will be reviewed. 

INERTISATION BACKGROUND 

“Inertisation”, is a technique that has been used around the world to enhance the safety of underground coal mine 

areas after a combustion event. The term refers to the fact that the atmosphere in the area is such that it can not 

sustain combustion, including ignitions, and is therefore “inert.” This can be accomplished by reducing the O2

component of the atmosphere to a level that will not sustain combustion of a gas or of a solid, such as coal, or by 

increasing the amount of an existing flammable gas, such as methane (CH4), to an atmospheric concentration above 

which it becomes nonflammable relative to the O2 concentration of the atmosphere. The O2 concentration can be 

lowered to levels below that of normal air through consumption by slow or fast oxidation processes or by the 

addition of inert gases such as N2 or CO2 which do not participate in the oxidation or combustion processes. Such a 

technique enhances safety: should an ignition source be present in an inert atmosphere, combustion would not occur. 

Additionally, as will be discussed here, creating such an inert atmosphere in an area of a coal mine where 

combustion is ongoing, can extinguish the combustion process. 

Use of inertisation techniques is generally more widespread in coal mining regions around the world than in the U. 

S. due to the more prevalent use of bleederless ventilation systems in active areas of coal mines in other countries, as 

opposed to the almost ubiquitous bleeder ventilation systems currently used in U. S. coal mines. Bleederless 

ventilation is common where the prevention of spontaneous combustion is a key parameter for the ventilation design 

of an active panel. Bleederless ventilation is an attempt to render the gob inert in that it permits the accumulation of 

CH4 and other nonflammable gases, while limiting the introduction of O2. This creates an inert atmosphere that will 

not sustain the self combustion of coal and, therefore, limits the potential for these types of hazardous fire events or 

as a potential ignition source for an explosion. While bleederless ventilation is rare in the U. S., the sealing of 
2 

abandoned areas to permit benign, inert atmospheres to accumulate and to limit the area requiring mine ventilation is 

common to all coal mining regions. 

Seals are ventilation structures that are designed to prohibit, or at least greatly minimize, the exchange of 

atmosphere between an abandoned area with any adjacent ventilated areas and are, therefore, often a key component 

of inertisation methods. In the U. S., as in many other world coal regions, seals are also designed to limit the 

potential that an explosion in a sealed area could impact the active mine areas or the safety of the mine workforce. 

Seals, even those virtually air-tight, do not ensure that the entire atmosphere in the sealed area is inert. Research and 

investigations have shown that the surrounding strata can permit an exchange of atmospheres between the sealed 

area and adjacent ventilated areas of a mine (Garcia, et al. 1995). Recent case study modeling work in Australia by 

Gale (2005) has likewise shown that strata interaction to mining can produce hydraulic conductivity changes in the 

strata and provides insight to the mechanism for these mine atmosphere exchanges. The sealed area most 

susceptible to not being inert is the periphery of areas adjacent to ventilated areas. The concern from the inertisation 

standpoint is mainly that O2 from the ventilated area will enter the sealed area and render the atmosphere flammable 

or capable of sustaining combustion, although the reverse flow of CH4 or O2 depleted air from the sealed area can 

also be a safety concern. 

INERTISATION AND PRESSURE DIFFERENTIALS 

Ventilating pressure, or more precisely pressure difference, is a key parameter for successful inertisation strategies. 

For inert sealed areas adjacent to ventilated areas, it is obvious that the pressure difference between the two areas at 

any point in time will dictate the direction and volume of the atmosphere exchange at any given resistance to fluid 

flow through seals and strata. For this reason, many mine ventilation engineers attempt to minimize this pressure 

differential. However, normal swings of atmospheric barometric pressure will upset the balance between the sealed 

area and the ventilated area. The absolute pressure in the ventilated area is a function of the ventilation system with 

its controls and barometric changes. The pressure in the sealed area is a function of its pressure relative to the 

reservoir pressure of strata gases and any relief mechanisms that it may have, such as exchange through strata or 

seals with a ventilated area (or the ground surface in very shallow circumstances) or boreholes to the surface. 

Greater controlled use of some of these relief mechanisms to regulate pressure differences between sealed and 

ventilated areas may be warranted in situations where maintaining the inert integrity of the sealed area or noncontamination of the ventilated area is a concern. For example, surface boreholes, when used to regulate pressure 

differentials, can be free-venting, forced to flow through an exhauster to create more negative pressures, or attached 

to a positive pressure inert gas supply system. For instance, as a result of the 1994 Moura #2 Mine explosion and 

resultant recommendations, some Australian coal mines pump inert gases into the partially sealed gob area of a 

panel immediately prior to and during panel sealing operations to inert the gob very quickly, i.e., within hours or 

directly following sealing (Brady, 1996). This procedure greatly reduces the time period necessary for the sealed 

gob to attain inert status, as opposed to solely relying on the CH4 and other strata gas emissions to inert the gob 

naturally. Observations during such studies have shown that the rates of natural CH4 gas emissions into sealed areas 

are very susceptible to small changes in pressure (on the order of 1-2 in. of water gauge) so that inertisation by CH4

gas is slowed as the pressure increases in the sealed area (Brady, 1997; Humphries, 1999). Similar observations of 

rather large variances in CH4 gas emission rates in development entries for relatively small changes in pressure have 

been noted by this author during conversion of gateroad entries from intake to return or visa versa, such as during 

longwall panel mining set-up. However, techniques such as pumping of inert gases into a sealed area, even though 

they increase pressure and slow CH4 gas emissions into the sealed area, can reduce the time period for the sealed 

area to inert and often result in the sealed area not going through the explosive range, greatly reducing a potential 

hazard (Balusu et al., 2002). 

A classic U. S. example of employing such inertisation control techniques is used at BHP’s San Juan Mine near 

Farmington, NM. Due to the potential for spontaneous combustion in the gob, San Juan is one of the few U. S. coal 

mines that use a bleederless ventilation system. At San Juan, gob and longwall face pressure are continuously 

monitored. The injection of N2 in the area immediately behind the longwall face and the operation of the gob vent 

boreholes (GVB’s) are controlled in unison to prevent atmospheric barometric swings from causing CH4 gas 

migration toward the face or O2 incursions into the gob. This example is also noteworthy in that it illustrates another 

major consideration for employing inertisation techniques, which is that the separation between the area to be 
3 

inerted and other areas may not always be a high resistance barrier such as strata and seals. In San Juan’s case, the 

barrier is the shields on the longwall face and the caving gob. 

However, in mine emergency situations, such as mine fires or explosions and resultant ongoing combustion events 

like those that will be discussed herein, the area to be inerted may have low or virtually no resistance barrier 

between other areas of the mine. As a result, relatively small pressure differentials can have a major impact on the 

inertisation process. In mine emergency situations where the miners have been evacuated and direct fighting of the 

combusting area becomes unsafe or impossible, the usual next step is to stop forced ventilation and seal mine 

openings to begin and assist the inertisation process. However, if unabated by higher resistance barriers such as 

seals, stoppings, or strata; relatively small pressure differentials like those caused by barometric pressure swings or 

natural ventilating pressure and/or other thermodynamic effects (e.g., temperature/ventilation effects due to the fire) 

can often carry large volumes of O2 rich mine air into the area of ongoing combustion to compromise the inertisation 

process. As a result, research is being conducted in the U. S. by the National Institute for Occupational Safety and 

Health (NIOSH) to develop a technique or techniques that can reliably place nearly air-tight seals remotely into 

strategic locations of a the mine to better isolate the combustion area and enhance and ensure the inertisation process 

(Gray et al., 2004; Trevits et al., 2005). 

Depending on where the combustion event is located in the mine, the use of inertisation techniques in mine 

emergencies often presents a major challenge to control and evaluate the process. The more isolated a combustion 

event is from other areas of the mine due to physical barriers and/or its location relative to the mine ventilation 

system, the more effective the inertisation process (Prebble et al., 2000). The Dotiki Mine fire in February of 2004 

is an example of the latter, as gas monitoring readings indicated that N2 being injected into the fire area, which 

seemed to be in a relative “dead zone” within the sealed mine, was successful in controlling and suppressing the fire 

even before the area was more isolated- from a ventilation standpoint- by the installation of 18 remote seals from the 

surface. 

LOW-FLOW INERTISATION 

Some inertisation applications, such as those involving underground coal mine emergencies, can be dealt with using 

inertisation methods and equipment which are limited, or only practical, in low volumetric flow ranges of one 

thousand to a few thousand cubic feet per minute (cfm). Examples of these low flow methods that have been 

successfully used in coal mining applications through boreholes are liquid or gaseous N2 or CO2 supplied by tankers, 

N2 supplied by a nitrogen membrane plant (although N2 pressure swing absorption plants could also be used), and 

the Tomlinson Inert Gas Generator which produces mainly inert gases from a combustion process. Tomlinson 

Boiler units have been used in coal mine inertisation applications in Australia since 1994 (Tomlinson Boilers, 2002). 

Most of the Tomlinson Boiler applications have been used to deal with spontaneous heating events and to inert gobs 

during panel sealing. Per the company’s product information, the flow rate of current Tomlinson Boiler units is 

approximately 1,060 cfm at about 14.5 psi, and the output gas composition is typically <2% O2, 75% N2, and 12.5% 

CO2 (Tomlinson Boilers). Actual field trials using Tomlinson Boilers have shown 02 to be in the range of 

approximately 2.5% and a small amount of CO- if adjusted correctly (Brady, 1997; Humphries, 1999). To date, 

Tomlinson units have not been used in the U. S. coal mining industry; however, liquid N2 and CO2 have been used 

for a number of years. Most recently, liquid N2 was used at the Dotiki, Excel No. 3 (late 2004-2005), Buchanan 

(2005), and to a lesser extent, Pinnacle (2003-2004) Mine fires. The liquid N2 is supplied by bulk tankers and is 

vaporized to a gas phase at the injection site. However, this delivery method can suffer from availability and 

transport distance issues and borehole accessibility due to rugged terrain which can result in delayed arrival times 

disrupting what should be a controlled injection process. More recently, N2 membrane plants, which typically can 

deliver 95-97% N2 in ranges of 500 to 1,000 cfm or more depending on plant size, have been used at the Excel No. 3 

and Pinnacle events (Smith et al., 2005; Smith et al., 2005; Trevits et al., 2005). Given their volumetric limitations, 

these low-flow methods and equipment are best suited to applications where localized inertisation can be employed 

and/or controlled, such as spontaneous combustion heating (Stephan, 2000). 

HIGH-FLOW INERTISATION- THE GAG 3A SYSTEM 

In some coal mine combustion events, localized or low-flow inertisation may not be effective or can be very time 

consuming. This may occur when there is a large area that cannot be controlled from a ventilation perspective or the 

location of the combustion event(s) can only be generalized, such as an event located in a gob environment. These 
4 

situations tend to occur in large underground coal mines using both room and pillar and longwall mining methods. 

The size and production capacity of these large mines compounds the financial, safety, and resource issues 

associated with these emergencies. Therefore, a need exists for a larger scale inertisation capability. The GAG 3A 

system meets this need. 

The GAG 3A system (figure 1) is based upon a Soviet designed agricultural jet engine which consumes aviation fuel 

with O2 from the intake air and exhausts combustion gases, primarily CO2 and H2O, along with the N2 from the air 

and small amounts of CO and H2. The system is designed to approach stoichiometric combustion (ideally, pure 

burning) that scavenges all the oxygen from the intake air. The GAG 3 A inertisation system technology was 

originally developed by the Polish mining industry in the early 1970s and has been used extensively in Poland, 

Czech Republic, China, and more recently to combat an extensive gold mine fire in South Africa. The initials GAG 

come from the Polish for gas to gas combustion. During a joint effort with the Polish Central Mining Institute 

(CMI) in 1982, testing of the GAG 3 A inertisation system technology was conducted at the U. S. Bureau of Mine’s 

(USBM) Safety Research Coal Mine in Bruceton, PA (USBM, 1982). For whatever reasons, the technology was not 

embraced by the U. S. coal mining industry at that time. The technology was further refined and successfully used 

in Poland and was imported into Australia in 1997 in response to some recommendations resulting form the Moura 

#2 explosion investigation. Currently, the hardware and trained system operators are maintained by the Queensland 

Mines Rescue Service (QMRS). More recently, two of these jet engines were purchased from Poland by Phoenix 

First Response1

, a subsidiary of Micon, Inc., a U. S. mining support company. A QMRS GAG 3A1 engine was used 

at Loveridge Mine (2003) and a Phoenix First Response unit, manned by Polish operators, at the Pinnacle Mine 

(2003-2004) events. A Phoenix First Response unit was also on standby for the Buchanan Mine fire (2005), but 

alternative fire fighting methods were ultimately used. 

Figure 1. Schematic plan view diagram of the GAG 3A Jet Engine System. 

The process of producing inert gases, utilizing a jet engine and associated equipment, involves the combustion of A1 

Jet fuel. The exhaust contains low O2 levels and high levels of CO2. CO and O2 levels, although low, vary 

according to back pressure on the jet exerted by mine resistance and ambient temperature. There maybe production 

of isobutene and isopentane dependent on fuel grade and additives but these will be at low levels. Volumetric flows 

from the system have been stated in the literature in the 50,000 cfm range, and as high as 64,000 cfm. However, the 

volume of the engine output is susceptible to the site specific backpressures experienced in a mine inertisation 

application. It is thought that these backpressures are a function of mine ambient temperature, gas mixture and 

buoyancy effects, barometric fluctuations, and mine resistance to air flow. While it was not possible- in the U.S. 

applications that follow- to accurately measure the volumetric GAG 3A system output, most observers felt that 

output was below this level. High backpressures, experienced at times during these applications, were probably the 

main reason for this conclusion. 

 

1

 Mention of a specific product does not mean endorsement of the product by NIOSH. 
5 

A specially designed afterburner (part of the engine in figure 1) is utilized to achieve near stoichiometric combustion 

(complete consumption of O2). This is achieved by varying fuel pressure, engine speed (air intake), and water 

cooling the tubes which contain the flame. The heat produced by the afterburner is as high as approximately 1,300OF 

in the chamber and temperatures of almost 3,200OF have been recorded at the flame tip. 

A diffusive cooler (figure 1) is utilized to serve a two-fold purpose. 

1. Provide a barrier between mine atmosphere and the GAG system. Maintained between critical maximum 

and minimum pressure requirements, so as not to impinge on the water curtain and create O2. 

2. Cool the exhaust gases prior to mine injection, typically to a 160O F to 190O F temperature range. 

This afterburner cooling device, under operational conditions, will produce H2 levels and higher O2 concentrations 

due to “thermal cracking” when the flame impinges on the water curtain. The concentrations produced have been as 

low as 5 ppm and as high as 8,000 ppm in the case of H2, while O2 concentrations have been seen as high as 0.5%. 

The steam exiting the system is slightly acidic and is known to have produced a secondary reaction with 

carbonaceous material and/or steel, resulting in the production of H2. The concentration levels of produced H2 have 

not been thoroughly studied during operations, but have been recorded as high as 125 ppm (differential between 

measured levels prior to entering the mine and mine detection system measured values some 7,200 ft remote from 

the mine inflow point). 

COMPARISON OF HIGH-FLOW WITH LOW-FLOW INERTISATION SYSTEMS 

As mentioned previously, low-flow inertisation systems have been successful in the proactive inertisation of gob 

areas and have the ability for total mine inertisation, but obviously a substantial period of time is required due to 

their low flow rates. To put it simply, large-volume units take less time to achieve the same results as the smaller 

capacity systems, but consideration must be given to the relative cost factors. Experience to date has shown that, 

where large volumes of inert gases are required, the GAG 3A system can deliver these large volumes on a lower cost 

per cubic foot of inert gas than many of the low-flow methods for which cost information was approximated during 

actual deployment of the systems. 

Each inertisation system has an optimum application dependent on the site-specific variables existing at a mine at 

the time of a combustion event. Experience has indicated that a risk based logic approach will aid in the selection 

and determination of the appropriate system for a particular application. To assist with utilizing an inertisation 

system of choice, the following table (Table 1) indicates both positive and negative variables for consideration prior 

to application. 

Table 1. Comparison of inertisation methods. 

Inertisation Method Advantage Disadvantage 

Large Volume Manpower (12 people/24 hrs)

Low cost per cfm Support Materials/Supplies

Mobility Training

Access to the mine ventilation system Higher O2 (than CO2 and N2)

GAG 3A Jet Engine 

Inertisation System 

Self Contained Fire gas ratios unstable (due to CO & H2 production)

Versatility Low Flow

Manpower (2 people/24 hrs) Time Duration

Portability High Maintenance

Tomlinson Boiler 

Minimal support materials/supplies Greater than 2% O2 Levels

Cool Low Flow

Denser than air (can be advantageapplication dependent)Method of application

Ease of movement Transport & Availability

CO2 Liquid and/or 

Gaseous 

Detection relatively easy Fire gas ratios unusable

Cool Low Flow

Lighter than air (can be advantageapplication dependent)Specialized Operators

Injection ability Transport & Availability

N2 Liquid and/or 

Gaseous 

Operational logistics relatively simple Detection requires specialized instrumentation
6 

GAG 3A SYSTEM UTILIZATION IN THE U. S. 

Loveridge Mine 

On February 13, 2003 a fire began in a trash car near the bottom of the slope in the Sugar Run area of the Loveridge 

Mine (figure 2). The mine is situated in West Virginia near the town of Fairmont and employs approximately 370 

people. The mine normally operates a longwall and continuous miner development sections. The mine owner, 

Consol Energy, is the largest underground coal producer in the U. S. and the operation at Loveridge is pivotal to 

their West Virginia operations. The company’s mines rescue response capability is structured around each operating 

mine, with a mutual response arrangement between the mines to ensure operational capability in the event of an 

extended incident at any of their operations. 

Figure 2. Sugar Run Bottom and slope area at the Loveridge Mine. 

After some direct fire fighting attempts, the Loveridge Mine was evacuated, the mine openings sealed, and six 

boreholes drilled in and around the fire area for monitoring and water pumping. By March 2003, attempts to 

suppress the fire with water pumped from the surface was not fully successful due to existing floor elevations that 

limited uniform and complete water dispersal through the fire area. In addition, there were concerns that there was 

sufficient air leakage through the mine opening seals to keep the fire in a presumed “smoldering” state. A decision 

was then made to attempt to inert the fire area using the GAG 3A jet engine technology. The QMRS was contacted 

to deploy an engine and operating personnel in a joint collaboration with Consol Energy, the U. S. Department of 

Energy (DOE), the National Institute for Occupational Safety and Health (NIOSH), the United Mine Workers of 

America (UMWA), and the Mine Safety and Health Administration (MSHA) (Parkin, 2005). A ventilation 

simulation of the inertisation situation at Loveridge Mine was done by the operator, which concluded that it was 

feasible to inert the whole mine. On March 8, 2003, preliminary plans for a means (a docking facility) to connect 

the GAG 3A system to the existing slope entrance structure were discussed and the design of the necessary 

components was begun. The slope, initially sealed with a make-shift seal, would permit the inert gases to travel to 

the fire area near the slope bottom and continue through the main entries of the mine to the other shaft areas 

(figure 2). 

On April 1, 2003, the QMRS teams arrived at Loveridge mine for site familiarization, identification of operational 

protocols, and requirements to be implemented prior to commissioning the GAG 3A system at the mine. As a result, 

two mine rescue people with breathing apparatus, support engineers/staff, drivers, and bulk fuel monitoring people 
7 

were identified as key Consol personnel to support the use of the GAG 3A system for an ongoing 24-hour-per-day 

operation. 

By April 4, 2003, the GAG 3A system had arrived at the Loveridge Mine site and, after some maintenance to the jet 

engine and its components, the system was commissioned for inertisation operations (figure 3). Set-up time for the 

system was approximately 11 hours. Following the first 12 hours of engine operation, it was noted that there was a 

need for additional cooling for the tube connections, as well as readjustment of some joints (afterburner connection 

flanges), and the input water pressure needed to be increased. On April 5, 2003, after 16 hours of run time, the slope 

seal was leaking steam and the outer connection to the slope (figure 4) developed gaps and was leaking badly. The 

engine was shut down while repairs were made. Instrument readings indicated that the engine was working against 

approximately 8 in of water gauge backpressure. 

Figure 3. GAG 3A jet engine and afterburner, Loveridge Mine. 

Figure 4. GAG 3A jet engine system interface with Sugar Run Slope. Note steam indicating exhaust gas 

leakage. 
8 

On the afternoon of April 6, 2003 the slope seal yielded with 9.5 inches water gauge registering on the gauge. 

Repair of the slope seal and connections permitted a shutdown and a visual inspection of the engine and its 

components. This inspection did reveal some degradation of the flame stabilizer rings, thought to be a result of the 

relatively high backpressure on the engine. The stabilizer rings were later replaced with Inconel®1

 steel flame 

stabilizer rings (a higher melting point than the original 316 stainless steel) and thereafter showed little sign of 

degradation. Other maintenance issues that surfaced were: a change of oil in the lubrication system had resulted in 

severe coking in the afterburner chamber, and the need for periodic engine shut down and inspection. By April 9, 

2003, boreholes and shafts in the Sugar Run area were outgassing and readings indicated the presence of the exhaust 

gases. Examples of the presence and effectiveness of the engine exhaust gases in the Sugar Run bottom area, 

indicated by the presence of exhaust gases (CO2 as the identifier) and the decrease in O2 are shown in figures 5, 6, 

and 7. By the sixth day of operation, the jet exhaust gases had reached St Leo shaft (figure 8) and by April 13, 2003, 

St Leo and Miracle Run fans were first started, which helped to pull inert gases through the mine from the Sugar 

Run bottom area. At 8 pm on April 15th, 2003, the first rescue team re-entered Loveridge, 61 days after the mine 

was sealed and 10 1⁄2 days after the GAG engine was started. The GAG 3A system was operated intermittently 

during the mine rescue re-entry operations until April 21, 2003, when operations were terminated. In total, the 

engine operated for 270 hours with minor servicing and replacement of consumable parts and the engine consumed 

an average of 423 gal (1,600 liters) of fuel per hour and 4,887 gal (18,500 liters) of water per hour. 

Figure 5. CO2 and O2 concentrations in Sugar Run Slope, Loveridge Mine. 

 “Event” as shown on the graph indicates GAG 3A operation (on/off). 

During its 17 days of operation at the Loveridge Mine , the GAG 3A system was able to render inert the Sugar Run 

bottom area and the over 9.5 miles of passageways at the Loveridge Mine by reducing the O2 concentrations (Conti 

et al., 2003). As a result, the mine rescue teams were able to safely re-enter the mine to explore and ultimately 

isolate the fire area, which still had indications of active combustion, and was further inerted with N2 injection and 

permanently sealed. At the time, this was the longest that the jet engine had operated for a mine inertisation 

application and some system components failed, but these occurrences were handled without major impact to the 

overall inertisation process. The potential benefit of more positive sealing of connections, ports, and mine seals was 

also recognized. Finally, the Loveridge Mine experience also provided a learning process for those involved and 

demonstrated that the GAG 3A system would be a valuable tool for fighting mine fires in the U. S. 
9 

Figure 6 - CO2 and O2 concentrations at borehole #1, Loveridge Mine. 

“Event” as shown on the graph indicates GAG 3A operation (on/off). 

Figure 7 - CO2 and O2 concentrations in borehole #13, Loveridge Mine. 

“Event” as shown on the graph indicates GAG 3A operation (on/off). 
10 

Figure 8. Map of the Loveridge Mine showing Sugar Run and other shaft locations. 

Pinnacle Mine 

At the Pinnacle Mine located near Pineville, WV, a series of four explosions occurred between August 31 and 

September 16, 2003 in the active #8 longwall district, shown in figure 9. Mine gas readings from the various 

monitoring boreholes indicated that there was active combustion ongoing at an unknown location in the longwall 

district. The operator began drilling additional boreholes into the longwall gateroads to detect the heat source. 

Phoenix First Response was contacted by the operator and arrangements were made to utilize the GAG 3A jet 

engine in an attempt to inert the approximately 9,000 ft by 9,000 ft longwall district to extinguish the fire. 

Arrangements were also made to have trained GAG operators from Poland man the operation of the jet engine. By 

October 1st, the engine had been set up at the 8A bleeder shaft (figure 9) and the operators had arrived. The engine 

was started late in the day after a crane had removed the bleeder fan elbow conduit from the shaft and replaced it 

with a specially designed GAG docking hood that was then fastened to the shaft coping (figure 10). This system had 

considerably less leakage issues than the Loveridge slope structure and temporary seal which were not as amenable 

to a pressurized, leak-proof connection. 

Prior to the GAG 3A engine start-up, NIOSH had been asked by the mine operator to provide technical assistance in 

locating the fire source. It was hypothesized that as the inert gas from the GAG engine pushed through the gob, 

there was a possibility that explosive mixtures of CH4 and O2 could be pushed through the fire zone, causing an 

explosion. NIOSH developed and implemented a plan to instrument five boreholes near the active longwall panel 

with sensitive pressure monitoring devices that could detect an explosion. If an explosion occurred, triangulation 

techniques could then be used to determine the point source of the explosion. Figure 11 depicts the #8 longwall 

district including the bottom of coal elevation contours, the active 8I longwall face, monitoring boreholes, and the 

final 12 NIOSH pressure transducer monitoring holes. However, at the time of the GAG engine start-up, only 

boreholes BH-1, BH-4, BH-5, 8-I-1, and 8-HI-1 were being pressure monitored. 

The GAG 3A system ran successfully through October 7th with only occasional operational or maintenance issues. 

S. Fork fan was operated and ventilation adjustments made to assist in drawing the inert exhaust gases toward the 

active longwall. Even so, as occurred at the Loveridge Mine, there were periods when the engine would see more or 

less backpressure from the mine. Theories as to why this was occurring abounded and included flow restrictions, 

barometric pressure influences, and an “air bubble”. Obviously, the exact cause could not be determined, but 

perseverance in terms of continuous operation of the engine seemed to overcome the variable backpressure problem. 
11 

Figure 9. Pinnacle Mine showing #8 Longwall District, 8A Bleeder fan, and active longwall. 

Figure 10. Photo of GAG 3A System set-up at 8A Bleeder Shaft, Pinnacle Mine. 

Note fabricated shaft hood for docking. 
12 

Figure 11. Pinnacle #8 Longwall District depicting bottom of coal elevation contours, 8I active longwall face, 

monitoring boreholes, and final 12 boreholes pressure monitoring boreholes (NIOSH). 

Tracking the underground movement of the exhaust gases via the monitoring boreholes in the #8 longwall district 

indicated that the exhaust gases initial migration was generally down-dip from the 8A shaft bottom, i.e., the 

structurally low northwest corner of the district inerted first and then the inerted zone gradually moved up-dip. 

Gravity (their higher density) may have been a reason for this, although ventilation (the operating S. Fork fan), 

ventilation controls, water accumulations, or gob resistance could also have been reasons in whole or in 

combination. 

By October 8th, the inert gas front was approaching the active 8I longwall area and the five pressure monitoring 

borehole sensors measured a sudden pressure increase attributed to a gas ignition or explosion. Determination of the 

location of this event was much more difficult than originally envisioned as it appeared that the pathway to the 

nearest pressure monitoring boreholes may have been mostly or entirely through the gob itself. The data was 

analyzed using three empirical methods based on 1) the arrival times of peak pressures, 2) the magnitude of the peak 

pressures, and 3) the difference of arrival time between peak one and two at each location. All three methods 

showed the most probable location of the source of the explosion to be in caved area of the active longwall panel, 

just inby the face. 

The time to initially inert the desired area of the mine took approximately 7 days, which is the length of time that the 

mine had originally estimated. The GAG 3A engine continued to be operated through October 19th in an attempt to 

maintain the inert area near the active longwall face. During this time, the pressure transducers measured another, 

much lower magnitude and less sudden, pressure increase on October 14th, indicating a possible explosion. Also 

during this time period, the mine operator, using a compressor, brought inert gases out of a borehole in the lower 
13 

elevation area of the longwall district, transported the gases overland via a pipeline, and pumped the inert gases into 

boreholes closer to the area of the suspected ignition source in the gob behind the active longwall face. In the time 

period following the inertisation process, a more extensive array of pressure monitoring was installed in the longwall 

district and the mine was alternately ventilated using different ventilation scenarios. This ventilation process was an 

attempt to determine whether the ongoing ignition source had been successfully and completely extinguished by the 

inertisation process. While gas readings did not show conclusively that combustion was ongoing in the area, 

concerns about the presence and interrelationship of relatively small amounts of H2, CO, and CH4 delayed re-entry 

until a localized inertisation plan was instituted early in 2004. This re-entry plan is presented by Smith (Smith et al., 

2005). The #8 longwall district was first temporally sealed and then permanently sealed in February and March of 

2004, permitting continuous miner production to resume on April 7, 2004. Following re-ventilation of the 

8I longwall panel in May, longwall production resumed on May 17, 2004. 

SUMMARY 

Underground coal mine fires and explosions are major events impacting miner safety, job security, the nation’s 

resources, and the financial well-being of coal producing companies. When such events arise and can not be dealt 

with directly, a suite of remote (from the surface) tools have been, and are being developed, to minimize the event’s 

impact and provide for the safe re-entry and re-start of the mining operation. A number of these remote techniques 

use the long employed mining concept of inertisation of the mine atmosphere, to suppress the combustion process to 

enhance the safety of the miners on re-entry, and to minimize the highly time-dependent impact of the event. Some 

of these events can use localized inertisation techniques, while others call for more generalized and larger area 

inertisation, or in some cases, a combination of the two. The Loveridge and Pinnacle Mine inertisation experience 

demonstrated the ability for the GAG 3A system technology to inert major portions of large mines to deal with 

combustion events and shorten the time frame for safe re-entry. Experience gained from these two applications of 

the technology and its potential use with other remote mine firefighting technologies will be of substantial benefit to 

the industry in responding to such future events in the U.S., if and when they should occur. 

REFERENCES 

Garcia, F., McCall, F.E., and Trevits, M.A., A Case Study of Methane Gas Migration Through Sealed Mine Gob 

into Active Mine Workings. Proceedings of the 7th U.S. Mine Ventilation Symp., SME, June 5-7, 1995, Univ. of 

Kentucky, Lexington, KY, pp 43-48. 

Gale, W.J., Application of Computer Modeling in the Understanding of Caving and Induced Hydraulic 

Conductivity about Longwall Panels. Proceed. Coal2005 Conference, April 26-28, 2005, pp 1-5. 

Brady, J.P., and McKenna, R.L., Sealing, Monitoring, and Low Flow Inertisation of a Goaf. Proceed. QCO/DME 

Coal Industry Safety Conf., Aug. 20-23, 1996, Yeppoon, Queensland, pp 161-166. 

Brady, J., Tomlinson Boiler, Inert Gas Generator Field Trails. Proceed. Queensland Mining Industry Health and 

Safety Conf., Sept. 9-12, 1997, Yeppoon, Queensland, pp 152-157. 

Humphries, P., Newlands Underground Spontaneous Combustion Monitoring and Management. Proceed. 

Queensland Mining Industry Health and Safety Conf., Aug. 22-25, 1999, Yeppoon, Queensland, pp 218-225. 

Balusu, R., Humphries, P., Harrington, P., Wendt, M., and Xue, S., Optimum Inertisation Strategies. Proceed. 

Queensland Mining Industry Health and Safety Conference 2002, Aug. 4-7, 2002, Townsville, Australia, pp 133-

144. 

Gray, T.A., Trevits, M.A., Crayne, L.M. and Glogowski, P., Demonstration of Remote Mine Seal Construction. 

SME Annual Meeting Preprint No. 04-194, February 23-25, 2004, Denver, CO, 8 p. 

Trevits, M.A., Smith, A.C., Ozment, A., Walsh, J., and Thibou, M., Application of Gas-Enhanced Foam at the 

Excel No. 3 Mine Fire. Proceed. National Coal Show 2005, June 7-9, 2005, Pittsburgh, PA. Web Pub. 
14 

Prebble, S. and Self, A., Spontaneous Combustion at the Blair Athol Coal Mine. Proceed. Queensland Mining 

Industry Health and Safety Conference 2000, Aug. 27-30, 2000, Townsville, Australia, pp 269-280. 

Smith, A.C., Trevits, M. A., Mucho, T. P., Ozment, A., and Walsh, J. B., Evaluation of Gas-Enhanced Foam for 

Suppressing Coal Mine Fires. Proceed. National Coal Show 2005, June 7-9, 2005, Pittsburgh, PA. Web Pub. 

Smith, A.C., Mucho, T.P., Trevits, M.A., and Cummins, M., The Use of Nitrogen-Enhanced Foam at the Pinnacle 

Mine. Proceed. National Coal Show 2005, June 7-9, 2005, Pittsburgh, PA. Web Pub. 

Tomlinson Boilers. Presentation for Dräger USA, 2002. 

Tomlinson Boilers Product Information. 

Stephan, S. and Blanch, M., Inertisation, Reducing the Risk and Solving the Problems: the Lessons of Three 

Years Experience Using Inertisation in the Northern Bowen Basin. Proceed. Queensland Mining Industry Health 

and Safety Conference 2000, Aug.. 27-30, 2000, Townsville, Australia, pp 281-294. 

USBM, CMI Inert Gas Mine Firefighting System. Contract J0318080, USBM Report, 1982. 

Parkin, R., Exhausting Work. Materials World. May 2005, pp 32-35. 

Conti, R. and Lazzara, C., Inertisation of the Loveridge Mine Fire Summary Report. NIOSH Internal Report, 

June 23, 2003.