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22
Prevention of Frictional Ignitions
Chapter Outline
22.1 Coal Seam Degasification 365
22.2 Ventilation 366
22.2.1 Development Heading in a Highly Gassy Mine 367
22.2.2 Longwall Face in a Highly Gassy Mine 367
22.3 Wet Cutting or Water-Jet-Assisted Cutting 368
22.4 Machine Design Parameters 370
22.4.1 Speed of the Bit 370
22.4.2 Size of the Bit 370
22.4.3 Angle of Attack 370
22.4.4 Material of Construction 371
22.5 Summary and Conclusions 372
22.6 Frictional Ignitions Caused by Belt Conveyors 373
22.6.1 Detection of Belt Fires 374
22.6.2 Preventing Belt Fires 374
References 374
Frictional ignition at the coal face is defined as rapid oxidation of either (1) a mixture
of methane and air or (2) a mixture of methane, coal dust, and air with a visible flame
that can last from several seconds to several minutes. Field studies done by the Mine
Safety and Health Administration indicate that in recent years, on the average, 71
ignitions occur in US coal mines per year as shown in Table 22.1. Mine fires caused
by conveyor belt friction will be discussed separately and later in the chapter.
It is interesting to note that most of the ignitions occurred in gassy mines of
Alabama, Virginia, Pennsylvania, Utah, and West Virginia. Since the early 1970s,
there has been no fatality in US mines because of frictional ignitions but injuries
have occurred. However, there are known cases overseas when a coal mine explosion
was caused by a frictional ignition when multiple fatalities were caused [1]. Besides,
production losses for at least a shift for investigation of causes of ignition can be very
expensive. Thus, frictional ignitions have a potential to create a mine disaster as well as
production losses, and every effort should be made to minimize them.
Necessary conditions for a frictional ignition to occur require (1) an ignitable
medium, usually a mixture of methane and air, (2) a minimum source of energy, gener-
ally created by coal cutting bit striking coal, sandstone, or pyrite, and (3) minimum
temperature to ignite the mixture.
Two common denominators in most frictional ignitions are the presence of
excessive methane and the presence of sandstone in the roof, floor, or as a middleman.
Advanced Mine Ventilation. https://doi.org/10.1016/B978-0-08-100457-9.00022-5
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