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No. 441, October 1994

SPONCOM-—AN EXPERT SYSTEM TO PREDICT
SPONTANEOUS COMBUSTION POTENTIAL
OF A COAL MINING OPERATION

Objective

Predict the spontaneous combustion potential of a min-
ing operation using an expert system computer program.

Background

Approximately 15% of underground coal mine fires are
caused by the spontaneous combustion of coal. Spon-
tancous combustion Gres usually occur in mined-out or
gob areas and are difficult to detect and to extinguish.
These fires present a serious safety hazard to mine person-
nel, often requiring sealing of large sections of the mine or
the entire mine. A knowledge of the spontaneous combus-
tion potential of the mining operation and the factors that
increase that risk can be useful in preventing spontaneous
combustion fires. This can be accomplished through the
use of aggressive monitoring and control measures at exist-
ing coal mining operations.

‘The self-heating of coal occurs when the heat produced
by low-temperature oxidation is not adequately dissipated,
resulting in a net temperature increase in the coal mass.
Under conditions that favor a high heating rate, a fire
ensues. Many factors can contribute to the spontaneous
combustion process in an underground mining operation,
These include the self-heating potential of the coal, the
coal properties, the geologic and mining conditions, and
the mining practices.

Approach

‘The SPONCOM expert system was developed by the
US. Bureau of Mincs (USBM) to aid USBM and US.
Mine Safety and Health Administration personnel, mining

operators, and consultants in the assessment of the spon-
taneous combustion risk of an underground mining opera-
tion. An expert system is a computer program that uses
available information to make decisions based on a serics
of rules provided by the programmer. It is an interactive,
user-friendly, and inexpensive method of conveying "expert"
advice.

To develop the program, information was gathered
from the literature, from interactions with experts in
ground control, ventilation, and geology, and from mine
personnel that have experienced self-heating events at their
operations. The information was correlated with the
USBM's experimental studies on the self-heating tend-
encies of coals to form the knowledge base for the expert
system,

How It Works

“The program is designed to obtain information from the
user on the coal properties, geologic conditions, mining
conditions and practices, and spontaneous combustion his-
tory for a mining operation, The program uses a series of
interactive data-input screens to prompt the user. During
the input process, "expand" screens are available to provide
specific information on each input parameter with respect
to its particular effect on the overall self-heating risk.

The program, written in ANSI C programming lan-
guage, determines the coal’s rank and relative self-heating
potential, based on the coal’s proximate and ultimate
analyses, heating value, and prior spontaneous combustion
history, The program then determines what effects the
coal properties, geologic and mining conditions, and
mining practices have on the spontancous combustion risk
of the mining operation, based on the coal’s self-heating
potential.

‘This document was prepared by the Bureau of Mines, Neither the United States Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the information contained in this document, or warrants that such use be free from

privately owned tights.



Two mechanisms contribute to the heat generation by
the coal, the heat of oxidation and the heat of wetting.
The heat of oxidation is the heat generated by the adsorp-
tion of oxygen by the coal. The reaction rate is temper-
ature dependent, increasing with increasing temperature.
The heat of wetting is the heat generated by the adsorp-
tion of water vapor by the coal surfaces. Coal properties
that affect the rate of heat gencration include the coal’s
reactivity, its moisture content, friability, and the presence
of pyrite and other impurities, The friability of coal is a
measure of its ability to be broken into smaller pieces.
While the friability of coal is not a heat-producing prop-
erty, more friable coals have a higher relative self-heating
risk because of the generation of fresh surfaces available
for oxidation and heat of wetting to occur. The program
determines the contribution of each of these factors to the
overall spontancous combustion risk.

Geologic factors that are included in the program’s
evaluation of the spontancous combustion risk include
those that affect the amount of coal exposed to air and
moisture, such as coal thickness, seam gradient, dikes, and
cleat density, and those that affect the reactivity of the
coal, such as the presence of geothermal sources and nat-
ural burn zones. Also included are geologic factors that
affect the transport of air and moisture to the coalbed,
such as depth of cover, faults, dikes, and channel deposits.
In addition, the presence of pyrite veins and rider beds in
close proximity to the coal seam, which can also react with
air and moisture, increasing the spontancous combustion
risk, is considered.

The mining conditions section of SPONCOM evaluates
the effects of mining conditions on the overall spontaneous
combustion risk of the mining operation. Among the con-
ditions considered are the degree of floor heave, which can
expose rider beds or pyrite veins that might be present to
air and moisture. The amount of rib sloughage, which con-
tributes to the amount of exposed coal surfaces susceptible
to oxidation in the mine entries, is also considered. The
effect of the ambient air temperature in the working area

is also evaluated, since the reaction rate of the coal ox-
idation is directly related to temperature.

The final section of SPONCOM assesses the effects of
mining practices on the spontaneous combustion risk, The
mining practices are the only factors that can be directly
controlled by the operator. The type of mining (longwall
or continuous), gate road pillar design, pane! dimensions,
coal thickness being mined, and rate of advance or retreat
are all important factors in determining the spontancous
combustion potential of a mining operation, These factors
control the amount of coal exposed to air and moisture
and the duration of the exposure. Other factors con-
sidered in this section are the face ventilation air velocities
and the caving height of the gob. These factors influence
the movement of air and moisture in the gob or mined-out
area.

The input data are stored to a data file, where it can
be recalled and updated as needed. The program output
gives the self-heating risk of the coal and provides details
on each of the factors that increase the risk of spontane-
ous combustion in the mining operation. These are dis-
played on the terminal and can be printed to a hard-copy
printer.

This information can be usefut in preventing spon-
taneous combustion fires through the use of aggressive
monitoring and control measures at the mining operation.

For More Information

To obtain a copy of the expert system program (on a
3¥einch diskette for IBM? personal computers or compat-
ibles) or for more information about the USBM’s spon-
taneous combustion research program, contact: Alex C.
Smith, Pittsburgh Research Center, U.S. Bureau of Mines,
Cochrans Mill Rd., P.O. Box 18070, Pittsburgh, PA, 15236,
telephone (412) 892-6766.

1Reference to specific products daes not imply endorsement by the
U.S. Bureau of Mines.

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