Page 416 - Advanced Mine Ventilation

Gas and Dust Explosions 385

Table 23.3 Minimum Ignition Energy for Mine Gases at 1 atm and 77 F

Minimum Energy, mJ
Combustibles Air Oxygen
Methane 0.30 0.003
Ethane 0.26 0.002
Propane 0.26 0.002
n-Butane 0.26 0.009
Acetylene 0.017 0.0002
Hydrogen 0.017 0.0012
Ethylene 0.07 0.01

23.1.4 Burning Velocities
Burning velocities of most mine gases are only a few cm/s, but it can increase to
40e50 cm/s at and around their stoichiometric concentrations. Assuming nonturbulent
flames, the maximum flame speed can be roughly estimated at eight times the burning
velocity, i.e., about 400 cm/s (13.1 ft/s). These numbers are well below the velocity of
sound. Detonation velocities are supersonic and range from 2500 to 2700 m/s for
typical mine gases. Only hydrogen has a detonating velocity that is close to
3000 m/s. In all cases, the maximum value is attained at a combustible concentration
slightly higher than stoichiometric concentrations.

Table 23.4 Minimum Autoignition Temperature for Mine Gases

Minimum AIT 8C
Combustible Air Oxygen
Methane 630 555
Ethane 515 505
Propane 450 NA
n-Butane 370 285
Acetylene 305 295
Ethylene 490 485
Carbon Monoxide 610 590
Hydrogen 520 400