Page 375 - Advanced Mine Ventilation
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346 Advanced Mine Ventilation
Table 21.1 Number of Fires in Underground Coal Mines [1]
Source Number of Fires Percent (%)
Electrical Short/Arcing 28 32
Flame Cutting/Welding 17 20
Spontaneous Combustion 15 17
Conveyor Belt Friction 15 17
Frictional Ignitions and Other Sources 12 14
Total 87 100
equipment minimizing the risk of fire. Flame cutting and welding is mostly a house-
keeping issue that can be made safe by training and enforcement of laws. Belt fires
are mainly due to friction and will be discussed under frictional ignitions. Major
remaining issues are the following:
1. Spontaneous combustion.
2. Frictional ignitions.
3. Gas and dust explosions.
These subjects will be discussed in detail in this and the following chapters.
21.1 Spontaneous Combustion of Coal
It is generally accepted that the spontaneous combustion propensity is related to the
rank of coal: the lower the rank, the more the coal is liable to spontaneous heating.
Other factors that may impact this phenomenon include heat of wetting, temperature
of coal, ventilation pressure differential, oxygen content of coal, particle sizes, geolog-
ical anomalies, and mining methods. It is always advisable to determine the liability to
spontaneous heating in the laboratory prior to planning the mining method for the coal
seam.
At present, there are three different techniques to measure a coal seam’s liability to
spontaneous combustion:
1. Adiabatic heating oven.
2. Temperature differential methods (also called crossing-point temperature method).
3. Oxygen sorption methods.
21.1.1 Adiabatic Heating Oven
Smith and Lazzara [2] ran an experiment on 24 coal samples, ranging from anthracite
to lignite, to determine the minimum temperature necessary to start the process of
spontaneous combustion and called it, “minimum self-heating temperature” or SHT.
Fig. 21.1 shows a schematic of the experimental setup.