Coal Mine Fires and Burning Refuse
Caveat: Coal mine fires or underground mine fires are generic terms for coal seam fires. The reason the “mine” is used within the description is due to the starting point of the fire. The majority of coal seam fires start within active or abandoned coal mines. It is important to note that the mine itself is not on fire, but the remaining coal pillars, remaining coal seam, poor quality coal, or burnable debris left behind is what burns.
Mine Fires: Majority of mine fires start through careless human activity, such as burning debris within an abandoned surface mine; however, mine fires can also start naturally via forest fires, lightning strikes, lava flows or other natural heat sources.
Underground coal mine fires occur around the world, sending thousands of tons of soot, toxic vapors, and greenhouse gases into the atmosphere, leading to pollution of surface and groundwater, mine subsidence as the coal is consumed, and ignition of forest and structural fires. Areas like the resort town of Glenwood Springs, Colorado has been plagued by series of suspected mine fire caused forest fires which burned thousands of acres of forest and many local residences.
Underground Mine Fire Thermal Cycle
When the fire travels into the ground from the surface it creates a thermal cycle. The thermal cycle consists of the fire heating the air causing it to rise and escape through passageways (fractures) in the ground. The points on the ground surface where the heated air discharges into the atmosphere are known as vents. The heated air carries the greenhouse gases, noxious fumes, soot, and smoke. These vents are extremely dangerous and pose a serious health risk. Vents encountered or discovered need to be avoided, never get closer than 100 feet to a vent.
With the hot gases rapidly venting, this creates a negative pressure at the fire face. Cooler, oxygenated air drawn from the outside atmosphere is pulled into the ground and ultimately to the fire, thus completing the thermal cycle. As the fire spreads into the coal seam new vents can form and old vents can change becoming intake vents.
According to e-AMLIS, in 2013 there were 98 underground mine fires in 9 states. This is considered to be an underestimate for the actual number of fires nationwide.
Coal mining states programs address mine fire and coal refuse fire related emergencies. These fire emergencies can threaten to ignite forest fires and underground mines fires that can burn beneath buildings, roadways and grounds releasing deadly gases and causing mine subsidence. Abatement methods range from complete excavation and quenching with water, to the use of specialty foaming cements and firefighting foams that are injected into the fire through boreholes drilled from the ground surface. Other techniques that may be used include the use of liquid nitrogen to extinguish the fire by the rapid removal of heat.
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Frequently Asked Questions
Types of mine fires:
- Burning coal seam: This type of underground fire follows the fuel source (carbon) along the coal seam. Based on geological structure, these fires break into two categories:
- Horizontal coal beds
- Coal seams which are generally flat lying. Occurrences are generally east of the Rockies and in Northern Alaska. Fires within these coal beds are typically easier to characterize and delineate.
- Angular beds
- These coal seams follow geologic structures such as anticlines and synclines. The angle degree can be up to 90 degrees. These type of coal seams occur within the Rocky Mountain and Southern Alaskan Ranges as well as the anthracite fields of Eastern Pennsylvania. Due to the angled bedrock, characterization and delineation of these fires can be difficult.
- Horizontal coal beds
This example is a burning coal seam where it outcrops. With the fire at the coal seam outcrop, there is plenty of oxygen in the air to cause the fire to burn rapidly with large flames. As the fire advances underground, the available oxygen will diminish limiting flame height and the fire takes on a smoldering appearance.
- Burning Refuse: These fires occur within coal waste piles or culm piles. Not confined to a singular seam, this fire type will burn from the ignition point spreading out into the pile. The difficulty in extinguishing these fires is due to the size of these piles. These piles can range in size from an acre to hundreds of acres, with the largest being 1.5 miles in length.
This is an example of a coal waste pile burning. Note how small the flames are. This is due to the material itself inhibiting the amount of available oxygen for the flame.
This image is an example of a burning refuse pile which has been mixed allowing more fuel (carbon) to reach the higher concentration of oxygen in the air. A product of bring fresh fuel to the surface causes the flames flash or flare up.
Mine fires or coal seam fires are Class “A” fires according to the U.S. Fire Administration. Class “A” fires burn materials such as wood, paper, cloth all of which leaves ashes. Common extinguishing methods for Class “A” fires is the use water or foam to cool or smother the fire.
A mine fire can also at times be a Class “B” fire when pockets of methane are encountered. This would cause a flash or fire ball which may burn for several minutes to several hours dependent on the amount of available methane. Fortunately, these Class “B” fires occur underground and would not be noticeable above the ground surface.
The ignition temperature for coal is dependent on the type of coal and its moisture content. The temperatures listed below are rough average temperatures of the types of coal as compared to wood.
Wood –572° F (300°C) Sustained burn 1472 to 1742°F (800 to 950°C)
Lignite – 525° F (274° C)
Sub-Bituminous – 662° F (350° C)
Bituminous Coal – 700° F (371° C)
Sub-Anthracite – 752° F (400° C)
Anthracite Coal – 1,700° F (927° C)
First of all, stay clear of the vent.
If the smoke or vent is near/entering a building or is in danger of causing personal or property damage, call 911.
If you discover a vent where there is not an immediate health or fire risk, contact your states abandoned mine lands office and notify them of your discovery.
When notifying your state via phone or email, please include or have ready the following information:
- Your name and telephone number
- Location of event or closest crossroads
- County and township or municipality
- And a description of the issue
- If able, provide picture(s) of the danger
How are mine fires extinguished?
There are several factors which can dictate how a mine fire is extinguished.
- Size of the area which is affected by the burning coal.
- Depth of the coal seam.
- Location of the fire within the coal seam and mined areas. Important to determine potential pathways the fire may progress.
- Length of time the fire has been burning.
- Local geology.
- Presence of methane.
- A few others
The reality of fighting underground fires is that a combination of methods presented below can be used as well as other firefighting techniques.
Like all fires, the faster the response time the greater the chances of extinguishing it with minimal costs and environmental damages.
A fire can only be extinguished by removal of one of the legs of the fire triangle, shown below. For coal to burn it must have a temperature of at least 150 degrees Fahrenheit, greater than 3% oxygen (21% oxygen in the air we breathe), and greater than 20% coal particles by volume. Removal of any one of these items will result in the fire extinguishing.