NIOSH MINE FIRE RESEARCH IN THE UNITED STATES 

Michael A. Trevits,1 Liming Yuan,2 Alex C. Smith3 and Edward D. Thimons4 

1National Institute for Occupational Safety and Health, P.O. Box 18070, 

626 Cochrans Mill Road, Pittsburgh, PA 15236, mft7@cdc.gov

2National Institute for Occupational Safety and Health, P.O. Box 18070, 

626 Cochrans Mill Road, Pittsburgh, PA 15236, lcy6@cdc.gov

3National Institute for Occupational Safety and Health, P.O. Box 18070, 

626 Cochrans Mill Road, Pittsburgh, PA 15236, aos6@cdc.gov

4National Institute for Occupational Safety and Health, P.O. Box 18070, 

626 Cochrans Mill Road, Pittsburgh, PA 15236, ebt7@cdc.gov

ABSTRACT 

During the time period from 1990-2007, there were 1601 reportable fires that 

occurred in the U.S. mining industry (an average of 89 fires per year). The leading 

causes of U.S. mine fires include flame cutting and welding operations, frictional 

heating and ignitions, electrical shorts, mobile equipment malfunctions, and 

spontaneous combustion. The National Institute for Occupational Safety and Health 

(NIOSH) is conducting a program of research addressing metal/nonmetal and coal 

mine fire prevention, detection, management and suppression. In the metal/nonmetal 

area, work was focused on technology transfer and training, and research to reduce 

the number of mobile equipment fires and their hazards. In the coal arena, research 

is underway to determine the root cause of cutting and welding-related fires and to 

evaluate the effects of ventilation schemes relative to the spontaneous combustion 

risk in longwall mines. Relative to fire management, research is ongoing on remote 

mine seal installation and remote mine fire suppression technologies. Finally, 

research is continuing to develop comprehensive and usable smoke management 

techniques and to develop mine fire growth models, propagation, and suppression. 

This paper presents a summary of some of the mine fire research and provides an 

overview of the next phase of the NIOSH mine fire research program. 
1. INTRODUCTION 

Mine operators in the United States were previously required by law to report to the 

U.S. Mine Safety and Health Administration (MSHA) any unplanned mine fire event 

that was not extinguished within 30 minutes of discovery (CFR, 2007). Subsequent 

to the accidents at the Sago and Aracoma Alma mines in January 2006, this 

regulation was modified to include all unplanned mine fire events that are not 

extinguished within 10 minutes of discovery (in surface mines and surface areas of 

underground mines, an unplanned fire not extinguished within 30 minutes of 

discovery). According to MSHA, in an underground environment, if miners attempt 

to fight a fire for 30 minutes and are unsuccessful, the fire will probably become 

uncontrollable. The revised reporting requirement will result in earlier fire-fighting 

plan activation as miners will notify supervisors more quickly who, in turn, can call 

in firefighting crews and allow miners to safely escape (Federal Register, 2006). 

During the time period from 1990-2007, there were 1601 reportable fires that 

occurred in the U.S. mining industry (an average of 89 fires per year) 

(DeRosa, 2008). Figure 1 shows the trend of mine fires for coal and metal and non 

metal mining operations (note, the upswing in the trend of the data for coal mining 

operations for the time period 2006-2007 may be a result of the change in the 

reporting requirements). The leading causes of U.S. mine fires include flame cutting 

and welding operations, frictional heating and ignitions, electrical shorts, mobile 

equipment malfunctions, and spontaneous combustion (NIOSH, 2009a). The fact 

that mine fires continue to occur reinforces the importance of recognizing and 

eliminating the potential hazards and the overall need for improved fire control and 

suppression technology to ensure the best possible outcome. 

Figure 1: Reported U.S. mine fires from 1990 to 2007 (DeRosa, 2008). 
The overarching goal of the NIOSH fire research program is to reduce the risk of 

mine fires through the development of new or improved strategies and technologies 

for mine fire prevention, detection, control and suppression. To accomplish this goal, 

NIOSH is conducting research aimed at ensuring that fire-safe materials are used, 

that combustibles are properly handled and stored, that mechanical and electrical 

equipment is properly used and maintained, and that personnel are adequately trained 

and educated in fire safety practices. NIOSH research is developing rapid and 

reliable fire sensing systems, guidelines for selecting and using these systems, 

investigating the principles of fire dynamics and the interaction of gaseous or 

chemical agents with an expanding flame. In addition, research is addressing the role 

that ventilation plays in fire control and extinguishment, and how different fire and 

smoke mechanisms can impact these interrelationships (NIOSH, 2009b). 

2. NIOSH MINE FIRE RESEARCH 

Current NIOSH research is focused on understanding and controlling spontaneous 

combustion, the causes of flame cutting and welding fires and injuries, the effects of 

ventilation on conveyor belt fire suppression systems and remote methods for 

addressing coal mine fires. The goal of this work is to reduce the number of fires and 

to improve mine fire control and suppression technology to ensure the best possible 

outcome during a mine fire. A report on the status of each program area follows. 

2.1Spontaneous Combustion

Spontaneous combustion continues to be a hazard for U.S. underground coal mines, 

particularly in western U.S. where the coal is generally of lower rank. For the period 

1990 – 2006, a total of 25 reported fires for underground coal mines in the U.S. were 

caused by spontaneous combustion (Yuan and Smith, 2009). Spontaneous 

combustion occurs when the heat that is produced by the low temperature reaction of 

coal with atmospheric oxygen is not adequately dissipated through conduction and/or 

convection, resulting in a net temperature increase in the coal mass. Coal oxidation 

is an irreversible exothermic reaction and its reaction rate increases with temperature 

and the increase in temperature leads to higher oxidation rate. If not averted with an 

appropriate action, this process results in the thermal runaway condition and a fire 

ensues. 

The spontaneous heating of coal often occurs in a gob area and may not be easily 

detected. The risk of an explosion ignited by a spontaneous combustion fire is also 

present in those mines with appreciable levels of accumulated methane gas. In fact, 

three of the mine fires mentioned above also resulted in subsequent methane gas 

explosions. The incidence of such fires and the associated explosion hazard is 

expected to increase with the projected increased mining of lower rank coals, deeper 

mines with more methane gas, and the growth in the size of longwall panels. 

A computer model has been developed from existing computational fluid dynamic 

(commonly called “CFD”) codes to describe the ventilation pathways through the 

immediate gob. CFD is a sophisticated computationally-based design and analysis 

technique that enables a user to simulate flows of gases and liquids, heat and mass 
transfer, multiphase physics, chemical reaction, and fluid-structure interaction 

through computer modeling. Using CFD, the user builds a 'virtual prototype' of the 

system or device and then applies real-world physics and chemistry to the model to 

generate images and data, which predict the performance of that design (Fluent, 

2009). 

In order to reduce the fire hazard from spontaneous combustion of coal in gob areas, 

NIOSH has conducted a series of computational fluid dynamics (CFD) simulations 

using coal kinetic data from the former U.S. Bureau of Mines laboratory-scale 

experimental results (Smith and Lazzara, 1987). Previous CFD models were 

developed to simulate the spontaneous heating of coals in a two-panel gob area using 

a bleeder ventilation system with a stationary longwall face (Yuan and Smith, 2007). 

Parametric studies were then conducted to examine the effects of coal’s activation 

energy, coal surface area, heat of reaction, different ventilation conditions and gob 

permeability distributions on the spontaneous heating process (Yuan and Smith, 

2008). CFD simulations were also conducted to model the spontaneous heating in 

longwall gob area using a bleederless ventilation system with a stationary longwall 

face (Smith and Yuan, 2008). Finally, CFD modeling of the effect of longwall face 

advance on the spontaneous heating of coals in a two-panel gob area using a bleeder 

ventilation system has been completed (figure 2) (Yuan and Smith, 2009). The 

results of this work will be used to assist in the design of ventilation systems where 

spontaneous combustion risk is high. 

Figure 2. Example plot of the temperature distribution (deg K) from CFD model 

with the longwall face at location No. 2 for 5 days (Yuan and Smith, 2009). 
2.2 Flame Cutting and Welding 

To determine the causes of the fires and injuries caused by flame cutting or welding 

operations, accident investigation reports were scrutinized, workers were 

interviewed, and flame cutting and welding operations at several underground coal 

mines were observed. The data from these investigations was analyzed and the 

following root causes of fires or explosions from flame cutting and welding 

operations in underground U.S. coal mines were identified (Monaghan, 2009). 

Failure to effectively check for methane gas. 

Failure to adequately inspect for fire during and after cutting or welding 

operation. 

Proper inspection of tools and equipment prior to starting the task was not 

sufficiently completed. 

Failure to remove combustible materials such as grease, oil, hydraulic fluid 

and, coal dust from the item to be cut or welded. 

Ensuring sufficient ventilation air at the work site. 

Failure to provide adequate training for the person performing the flame 

cutting or welding operation. 

Promising direct interventions to prevent the root causes of flame cutting and 

welding fires were identified and evaluated in field tests at operating underground 

coal mines. Existing training methods and procedures were examined and 

improvements to these methods and procedures were developed and tested in the 

field. 

2.3 Conveyor Belt Fire Suppression 

NIOSH, in partnership with the Mine Safety and Health Administration (MSHA), 

initiated a test program to determine the effectiveness of fire suppression systems on 

conveyor belt fires in entries with high-velocity air flow (figure 3). Full-scale 

experiments evaluated the effectiveness of dry powder chemical suppression systems, 

water sprinkler systems, and water deluge systems in simulated conveyor belt entry 

at air velocities of 2.5 to 2.8 m/sec (500 to 550 ft/min) and 6.7 to7.6 m/sec (1,350 to 

1,500 ft/min) (Rowland III et al, 2009). The data from this work will be used to 

develop guidelines for the installation and use of fire suppression systems in 

ventilated belt entries. In late 2007, the scope of this research was modified to 

include the recommendations made by the Technical Study Panel on the utilization of 

belt air and the composition and fire retardant properties of belt materials in 

underground coal mining (Mutmansky et al, 2007). NIOSH will conduct research to 

improve fire suppression systems by evaluating new technologies, new nozzle 

designs, spacing of nozzles, and system activation temperature. Tests on two waterbased suppression systems, a water sprinkle and a deluge type water spray, show that 

the systems were able to suppress test fires. However, the amount of water needed to 

suppress the fire to the point where a miner could walk up to extinguish any 

smoldering belt was greater than the current MSHA regulations require. MSHA 

regulations only require 10 minutes of water supply to the suppression system. In this 

test set-up, it is unlikely that either of these systems would have suppressed the fire 

had the water been turned off to the system after 10 minutes, based on visual 

observation. Test on two dry chemical suppression systems provided mixed results 
as one system did not extinguish the fire in either air-velocity condition. This system 

uses a nominal weight of 300 lb of dry chemical agent and 40 nozzles to protect 50 ft 

of fire resistant conveyor belt. The primary failure mechanism was damage to the 

hoses from the fire prior to system activation. Several of the nozzles in system A did 

not discharge any dry chemical agent because the hoses leading to the nozzles were 

severely damaged by the fire. The dry chemical fire suppression system B performed 

well at the lower air velocity; however, at the higher air velocity mixed results were 

obtained (Rowland III et al, 2009). 

In a related study, conveyor belt, typical of the type used in metal/nonmetal mines, 

where no mandatory fire resistance standards apply, were evaluated for their fire 

resistance. The results clearly showed the hazards of using non-approved conveyor 

belting and demonstrated that the use of approved conveyor belting can significantly 

reduce potential fire hazards. 

Figure 3: Conveyor belt fire suppression system set-up at the 

NIOSH Fire Suppression Facility (Rowland III et al, 2009). 

2.4 Remote Methods for Addressing Coal Mine Fires

The ability to remotely address coal mine fires can reduce worker exposure to 

hazardous situations. The objective of this work is to evaluate, improve or modify 

remote fire-fighting technologies, including remotely installed mine seals (ventilation 

barriers), and fire control and suppression technology. This research effort is being 

conducted with active industry participation and with the input from MSHA technical 

specialists serving as research partners. 

Full-scale remote mine seal installation experiments have been conducted to evaluate 

cement-based and rigid-foam based materials at the NIOSH Lake Lynn Experimental 

Mine (LLEM). The LLEM (located approximately 97 km (60 mi) southeast of 

Pittsburgh, Pennsylvania) is a world-class, highly sophisticated underground facility 

where large-scale explosion trials and mine fire research is conducted. This work has 
resulted in new understandings of the limitations of the technology and development 

of novel downhole tools to facilitate accurate placement of mine seal materials. 

Preliminary research on nitrogen gas-enhanced foam (foam resulting from 

commingling of nitrogen gas, water and a specialized foam concentrate) shows that 

foam can be stable in the mine opening and can accumulate and flow through mine 

workings (figure 4) (Smith et al, 2005). 

2.5 Testing of Temporary Ventilation Control Devices 

NIOSH in partnership with Strata Products tested the sealing capability of 

Ventstop®TM1

1

 Mention of a specific product or trade name does not imply endorsement by 

NIOSH. 

as part of an ongoing program to evaluate promising technologies. 

Ventstop®TM is a multi-purpose, inflatable device produced by Minvent Solutions 

and is available world wide for use in the metal and nonmetal mining industry. 

Ventstop®TM is used as an emergency seal (temporary ventilation control device), 

controlling ventilation in breakthrough situations, radiation dust, thermal heating 

return vent, blast fumes, fires, pass plugs and shaft sealing system. The device is 

reusable and can be placed in horizontal and vertical mine voids. Ventstop®TM was 

introduced into the Australian Coal Industry in 2005. 

Deployment, multi-day inflation and air leakage tests were conducted at the LLEM to 

determine the capability and limitations of Ventstop®TM in a simulated coal mine 

setting (figure 5) (Trevits, 2009). During the tests, Ventstop®TM was also subjected 

to low level forces of a nearby methane gas ignition. Testing showed that 

Ventstop®TM could be quickly deployed by two persons in approximately 7.5 minutes 

(to install the unit from the carry bag to full inflation in the mine opening and 

5.5 minutes to inflate the unit only). Deflation of the unit, folding and replacement 

into the carry bag took about 15 minutes (11 minutes to deflate the unit only). Air 

leakage testing showed that the unit could provide an effective temporary mine seal 

that could be further enhanced through the application of a polyurethane (PUR) 

sealant. Inflation of the unit for extended periods of time (24 hrs or greater) is 

possible through the use of a pressure demand control system. In these tests, mine 

ventilation air leakage rates were between 1.6 and 5.0 m3/min (55 and 175 ft3/min) 

depending on inflation pressure without the use of PUR sealant. When PUR sealant 

was applied to the unit, air leakage rates were substantially reduced by 85%. Preand post-methane gas ignition tests show that air leakage past the Ventstop®TM unit 

was not affected by the forces of the pressure pulses from the ignition. 

 
Figure 4: Compressed air gas-enhanced foam accumulating behind and moving 

through crib block sets at the LLEM (Smith et al, 2005). 

Figure 5. Underground testing of an inflatable temporary ventilation control device 

(Trevits et al, 2009). 

It is thought that Ventstop®TM could be used by the US coal mining industry to 

temporarily close an underground mine area in response to a fire or spontaneous 

combustion heating event, to temporarily redirect mine ventilation during longwall 

equipment moves or during stopping construction. 

3.0 FUTURE RESEARCH 

Planned work under the NIOSH mine fire research program will continue the 

spontaneous combustion modeling effort. The work will focus on western U.S. coal 

mines by simulating longwall gob areas and collaborating with western U.S. coal 

mine operators to collect spontaneous combustion data to calibrate the CFD model. 

CFD modeling will also be used to investigate nitrogen gas injection strategies to 

prevent the spontaneous heating in coal mines using bleederless ventilation systems 
and to suppress the spontaneous heating in coal mines using bleeder ventilation 

systems. It is hoped that this work will result in improved understanding of the 

conditions that lead to heating events and should also result in new ventilation 

practices and technologies to reduce the risk and number of fires. 

The conveyor belt fire suppression program will focus on the reduction of the 

hazards of underground coal mine fires, particularly in conveyor belt entries, by 

applying recent technological advances in the areas of fire-resistant and fireproof belt 

materials, belt fire suppression systems, atmospheric monitoring systems, and 

computer codes for predicting and assessing in real-time the impact of fire on the 

mine ventilation system. In addition, the work will include an overall evaluation of 

the flammability of conveyor belts, modeling of conveyor belts fires, modeling of 

contaminant spread, fire risk assessment, and training and maintenance. It is 

expected that the research output from this work will substantially reduce the number 

of fires and injuries/fatalities due to conveyor belt fires and will significantly improve 

the level of fire safety in mines.

4.0 SUMMARY 

Mine fires represent one of the greatest threats to those working in the underground 

mine environment. NIOSH mine fire research is addressing a wide spectrum of 

problem areas facing the U.S. mining industry. The intent of the research is to 

provide the mine operator and miners with an understanding of the conditions that 

could lead to a fire, the capability to detect unusual heating or fire conditions, and the 

technology to suppress and extinguish a fire to ensure the best outcome possible. 

Research papers that discuss much of the work presented in this article are available 

through the NIOSH mining website. A discussion and description of the NIOSH 

Mining Research Program and copies of all NIOSH published mining research work 

can be obtained by browsing to http://www.cdc.gov/niosh/mining. 

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