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]
D. Linear Heat Detecting Cable [18]
E. Point Flame Detectors [19]
F. Obscuration detectors employing infra-red beams [20]
G. Pneumatic detectors with fusible bulbs [21]
14-5 Fire Fighting [22] Techniques
Coal fires are reported from coalfields in China, India, Indonesia, Venezuela, South Africa, USA, Australia, Germany and many other countries. But while coal fires in developed countries are mainly under control, the technique for effective fire fighting is lacking in newly industrializing countries.
Depending on the situation, e.g. location, depth, size or age of the coal fire there are different techniques existing to extinguish [23] them. Some of the methods are listed below. They can be operated alone or used in combination:
A. Cooling down with water or injecting liquid nitrogen [24]
B. Taking out burning coal by bulldozing [25] or blasting
C. Cut-off air supply by covering and/or filling cracks [26] with soil or slurry
Normally the direct method is to bring the fire under control through the use of suitable extinguishing agents [27] or coolants (for example water). Loading out the fire can also be tried if the fire is not large and is approachable. If the above attempts are not effective and are likely to endanger [28] the safety of the personnel - than in such cases sealing off [29] the fire is advisable. In the majority of endogenous fires in mining shafts, the method of "sealing off" is applied.
NOTES TO THE TEXT
[1] mine fires：矿井火灾
[2] spontaneous combustion：自然发火
[3] natural hazards：自然界造成的危险
[4] old generators and lighting systems：老的发电机和照明系统
[5] spray sparks：喷溅的火花
[6] outer influence：外部的影响
[7] accumulation：积累
[8] transported substance：被运输的物质
[9] mechanical fault：机械故障
[10] friction：摩擦
[11] initiate：开始，发动
[12] welding or cutting operations：焊接和切割作业
[13] smoldering：熏烧
[14] fire detection：火灾探测
[15] collective reflectors (thermo-couple hoods) ：聚合反射器（热电藕罩）
[16] ionization & optical point smoke detectors：电离和光学的点烟雾探测器
[17] point heat detectors：点热量探测器
[18] linear heat detecting cable：线热量探测电缆
[19] point flame detectors：点火焰探测器
[20] infra-red beams：红外射线
[21] pneumatic detectors with fusible bulbs：带可熔化球的压气探测器
[22] fire fighting：消防，防火的
[23] extinguish：熄灭，扑灭
[24] injecting liquid nitrogen：注入的液氮
[25] bulldozing ：用推土机推
[26] covering and/or filling cracks：覆盖和（或）充填裂缝
[27] extinguishing agents：灭火剂
[28] endanger：使遭到危险，危害
[29] sealing off：密封
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