Geology Reference
In-Depth Information
Heat gain
Crossover point
Heat loss
Temperature increasing
Figure 2.4.1. Rate of heat loss and rate of heat gain versus temperature. From Kim et al. 1993.
termed l00% total air. Because the conditions for combustion are never wholly ideal, the theoretical air require-
ment must generally be augmented to achieve complete combustion. Analyses of the gases leaving a combustion
process can indicate the relationship between excess air and the types of fuel being burned. A variety of fuels can
participate in the combustion process including coal, wood, tar, pitch, and coke, among others. Day-to-day and
hole-to-hole variations in gas composition may reflect actual differences in fuel type, but may also reflect
variations in mine level ventilation and other factors.
A number of other parameters and indices have been devised by physical chemists to express relationships between
combustion products derived from mine fires. Although largely developed in a controlled laboratory environment,
these relationships have been successfully employed in determining the status of fires in active mines. The
application of these parameters and indices to abandoned mines is more tenuous. Yet, much useful information
can come from these gas analyses, particularly when used in conjunction with borehole temperature data. It is
beyond the scope of this chapter to delve into the details of these various parameters.
Abatement
M ine fire control is comprised of two components: isolation (containment) and extinguishment. Isolation
entails blocking or severing all potential avenues for the spread of fire. Extinguishment entails eliminating
the fire. To extinguish a fire, either the fuel or the oxygen supply must be removed or the temperature (of the
fuel) must be reduced below the limits required to support combustion. Removing any one of these legs of
the fire triangle will result in extinguishment. Depending on the particular situation, these components
constitute the three legs of the fire triangle illustrated in Figure 2.4.2 and may be addressed singly or in
combination.
The components of the fire triangle can be further subdivided into conventional mine fire control techniques and
more or less unconventional or unproven mine fire control techniques. The former includes conventional con-
struction procedures such as total excavation (of the burning seam), isolation trenches, and mine void filling. The
latter may include less conventional or novel techniques including chemical treatment (including nitrogen
entrainment in foam), in situ coal gasification, and burn-out control (Michalski et al., 1997).
The success of a fire abatement measure often depends on whether the mine is active or abandoned,
regardless of the method of mining. Fires in active underground mines are often discovered quickly, through
an explosion or through detection by monitoring which results in quickly implemented abatement measures.
It is important that abatement in an active mine is attended to in a timely manner so as to prevent loss of life
and to minimize lost coal production. The sudden emergence of a young fire is slow to heat the overburden
and condition the coal that enhances susceptibility to ignition. Fire abatement measures in an active mine
Search WWH ::




Custom Search