Page 111 - Advances In Productive, Safe, and Responsible Coal Mining

Mine ventilation networks optimized for safety and productivity 95

Face Face

Dynamic
EGZ
seal

Gob
Gob Headgate

Tailgate
Tailgate
Headgate
A B

(Not to scale)

Fig. 6.6 Typical development of an EGZ in a progressively sealed gob (left) and formation of a
continuous, dynamic seal (green, right) that separates the fresh air (blue) from the fuel-rich zone
(yellow), eliminating the EGZ.

6.7.3 Prevention of spontaneous combustion
Spontaneous combustion is the tendency of coal to react with available oxygen and
burn. Spontaneous combustion is a combination of complex chemical reactions that
are the subject of research worldwide and that are not yet fully understood. Not all
coals have a propensity for spontaneous combustion. For example, most coals mined
in the eastern US are usually not susceptible. European, Australian, and some Central
and Western US coals must take precautions. Spontaneous combustion happens when
the coal is exposed to sufficient amounts of oxygen to support the chemical reaction
and when the air flow is insufficient to take away heat. Therefore, fractures and failing
pillars, gob areas, and areas of geologic disturbance such as fault zones and intrusions
frequently create conditions in which coal can spontaneously combust.
Combustion is noticed by an increase in CO measured in return airways, often com-
bined with a characteristic odor of volatile hydrocarbons that are released as the coal
heats. Unless controlled quickly, spontaneous fires can grow rapidly and lead to cat-
astrophic loss of the mine. Spontaneous combustion can be controlled by isolating and
progressively sealing all mined-out areas, injecting nitrogen or other inert gases; for
example, exhaust gas from kerosene boilers. If spontaneous combustion is a known
hazard, the mine must be set up to quickly flood-affected workings with inert gas.
Continuous monitoring of all exhaust air streams and rapid response to any increase
of CO are essential to managing the spontaneous combustion risk.