Page 408 - Advanced Mine Ventilation

23
Gas and Dust Explosions

Chapter Outline

23.1 Gas Explosions 378
23.1.1 Definitions 378
23.1.2 Flammability Limits of GaseAir Mixtures 379
23.1.3 Ignition Requirements 383
23.1.3.1 Minimum Ignition Energy 384
23.1.3.2 Ignition Temperatures 384
23.1.4 Burning Velocities 385
23.1.5 Temperatures of Explosions 386
23.1.6 Pressure Rise in Explosions 386
23.1.6.1 Deflagration 387
23.1.6.2 Detonation 387
23.2 Dust Explosions 387
23.2.1 Explosive Limits of Dust in Air 388
23.2.2 Minimum Ignition Energy 389
23.2.3 Ignition Temperature 389
23.2.4 Dust Explosion Pressure 391
23.3 Prevention of Gas Explosions 391
23.3.1 Methane Drainage 391
23.3.2 Ventilation 391
23.3.3 Preventing Ignition of MethaneeAir Mixtures 392
23.3.4 Prevention of Dust Explosions 393
23.3.4.1 Effect of Volatile Matter in Coal 393
23.3.4.2 Effect of Moisture 394
23.3.4.3 Effect of Methane in Air 394
23.4 Stone Dust Barriers for Explosion Propagation Prevention 396
Problems 397
References 397

The history of coal mining is replete with mine explosions resulting in great loss of
lives. In the United States alone, at least 8000 lives have been lost to mine explosions
[1]. Table 23.1 provides a list of some major disasters in the past (1936e93).
As discussed earlier, coal seams and methane in coal are syngenetic in origin.
Methane is released when coal is mined. Methane air mixture becomes explosive at
5% at the lower level. If this mixture of gases meets an ignition source, such as an elec-
tric spark, or an open flame, it explodes creating a gas explosion. If not controlled, it
can build on intensity and become a “detonation” that travels at a speed faster than
sound. This creates a pressure front (shock wave) that kicks coal dust into air. If the

Advanced Mine Ventilation. https://doi.org/10.1016/B978-0-08-100457-9.00023-7
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