14-1 Factors Causing Mine Fires

Coal as a fossil fuel can catch fire by both natural and man-made causes. Some causes of coal fires can be found in:

A. Spontaneous combustion [2]

B. Forest fires close to coal seams

C. Traveling fire from one seam to the other

D. Natural hazards [3] (e.g. thunderstorms)

E. Old mining techniques (e.g. insufficient ventilation of the mine shafts, old generators and lighting systems [4] that spray sparks [5])

F. External heat sources (e.g. illegal distillation of alcohol in Indian coal mines)

G. Human induced (careless acts of mine workers)

14-2 Spontaneous Combustion:

Spontaneous combustion is one of the most frequent reasons for coal fires. The term 'spontaneous combustion' means that coal can start to burn without any recognizable outer influence [6]. It is caused by coals ability to react with oxygen contained in the air. As a result of the oxidation process the temperature of the coal starts to rise. If the temperature reaches a certain temperature noxious gases are produced such as carbon dioxide. Finally, if the temperature still continues to rise the coal reaches the flash point and starts to burn.

Spontaneous combustion depends on:

A. Coal type

B. Temperature

C. Availability of oxygen

D. Exposure to surface

E. Thickness of coal seam

F. Methods of mining

14-3 Conveyor Fires

In the conveyor structure, material (such as coal) that falls from the moving belt, or an accumulation [7] of settled dust from the transported substance [8], provides a ready source of combustible matter.

A mechanical fault [9] in the bearing of a roller, or friction [10] caused by the build up of coal around a roller, or a friction fault on the belt itself, may result in a heat source sufficient to initiate [11] combustion (fire).

Tests have shown that hot objects such as metal falling from welding or cutting operations [12] do not readily ignite coal. It is also evident from tests that even a mass of several kilograms of red hot metal when placed on top of or into coal dust or 'fines' will not impart sufficient energy to cause a smoldering [13] combustion process (smoldering is considered to be the increase in temperature of a slowly increasing volume of coal over a long period). Many kilowatts of energy are required to raise the temperature of coal to the point where smoldering occurs leading to gases being generated which subsequently ignite.

14-4 Fire Detection [14]

Many different types of fire detectors have been tried for coal conveyors over the years including:

A. Collective reflectors (thermo-couple hoods) [15]

B. Ionization & optical point smoke detectors [16]

C. Point Heat Detectors [17]

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