APARTMENT:
BUILDING

APARTMENT
BUILDING

LEGEND
© Borehole
[25 Heated zone

E53 cota zone
[Jno dota

° too — 1090 Elevation

‘Scale, tt

Figure 15.—Site map showing heated and cold areas inferred from Bureau’s mine fire diagnostic

technique.

|APARTMENT| APARTMENT}
BUILDING BUILDING ,7~ YAPARTMENT|
¢ BUILDING

c se

CO Fis- 7)

. /
/ 15°
Sf

ae

LEGEND

© Borehote
20° Temperature °C

Approximate snow melt
(Feb. 12, 1987)

[J Heated zone boundary

° 100 {7 cota zone boundary

Figure 16.—Site map showing heated and cold areas, snow melt regions, and borehole temperatures.

Scale, ft ——_———


Induced mine gas flow

KEY
© Suction hole
© Communicating hole

(+) Combustion gas present

(-) No combustion
gas present

(+)
G) Possible fire location

(+)

@---O----.0-

(+)
©

@--

A Bawa.

Case A

(+)

--0----O-

Figure 9.—Mine fire diagnostic technique.

acres. The surrounding boreholes are capped during suc-
tion to limit dilution by atmospheric gases.

At Carbondale, a primary concern was whether the
borehole casing diameter and depth would allow enough
underground gas flow throughout the fire zones to obtain
meaningful pressure and gas measurements. Pressure
drop due to flow of gas through the borehole casing during
suction is a major design consideration in sizing the ex-
haust fan, casing diameter, and other hardware. A variety
of borehole casing dimensions have been used in monitor-
ing abandoned mine fires. To maintain proper airflows
during communication tests, 8-in-ID casing was found to
be adequate for pipe lengths of 100 ft or less. This
diameter casing also allows adequate space for lowering
borehole monitoring equipment such as water sample bot-
tles, cameras, pressure transducers, and thermocouples.
Boreholes for the Bureau’s diagnostics are normally drilled
to a predetermined depth beyond coal-bearing strata of in-
terest and are cased with 8-in-diameter pipe to the top of
the first evident coal seam. Although attempts are made
to drill into voided areas, boreholes that are drilled into
nonvoid regions are generally still within the airflow

path, as determined from suction test pressure measure-
ments, and are therefore considered valid monitoring
points.

At Carbondale, the boreholes were drilled and cased
before the Bureau’s diagnostic techniques had been con-
sidered, In most of the boreholes, the 6-in-ID steel casing
extended through one or both coal seams. A pipe flow ve-
locity and pressure test was conducted using a 40-hp ex-
haust fan connected to a 90-ft length of 6-in-ID casing,
The pressure at the end of the casing was measured with
a Magnehelic’ pressure gauge (rates at 0- to 40-in vacuum
water column (w.c.)). The results of this test indicated
that a 20-in vacuum pressure drop could be expected for
every 100-ft length of 6-in casing. Use of two fans con-
figured in series increased the potential vacuum to 80 in to
overcome the borehole sizing constraints,

A special borehole instrumentation cap was designed to
facilitate both borehole monitoring and easy attachment of
a suction fan. The borehole instrumentation cap (fig. 10)

Reference to specific products does not imply endorsement by the
US. Bureau of Mines.


2? gp 4

UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT |

degree Colsius hp horsepower
cubic centimeter in inch
foot pet percent

square foot ppm part per million



16

boreholes (19 through 22) on the north-northeast perim-
eter of the site. The size of the boreholes and their dis-
tance from the other boreholes may have contributed to
this effect.

Figure 16 is a Carbondale site map with the results of
the Bureau’s diagnostic technique (heated and cold zones),
surface snow melt areas, and baseline borehole tempera-
ture measurements. In general, areas of snow melt can

be related to heated zones. Elevated borehole tempera-
tures (> 50° C) do not exhibit a consistent correlation with
either combustion zones or areas of snow melt. Both
borehole temperatures and surface temperatures are in-
fluenced by heat transfer due to the movement of hot
gases. Such movement through a mine or through the
overlying strata does not necessarily follow straight-line
paths in either the horizontal or vertical directions.

CONCLUSIONS

The mine fire diagnostic method incorporates a sam-
pling method that increases the detection zone of normal
point-source measurements by inducing gas movement
over distances greater than 200 ft. Measuring changes in
a characteristic of the moving gas, ie., hydrocarbon con-
centration, and plotting the results as vector quadrants
rather than as points provides interpretive insight and
bounds the area affected by combustion.

The mine fire diagnostic study at Carbondale indicates
that most of the heated zones lie below unoccupied areas
to the north of the apartment buildings. However, the
outer limits of the heated coal zones could underlie sur-
face areas adjacent to the buildings. Regular monitoring
of all boreholes for subsurface temperature, pressure, and
concentrations of methane, carbon monoxide, and carbon
dioxide would indicate the status of the fire and give warn-
ing of any changes in combustion activity.

It should be noted that while zones of heated coal and
cold coal were definitely located at the site (the bounded
areas in fig. 10), there are areas where the communication
data were insufficient to allow the definition of a hot or
cold zone. It should also be noted that there is some de-
gree of uncertainty in the extent of heated and cold zones.

However, the results of the mine fire diagnostic technique
are generally consistent with the snow melt evidence.
There was no direct correlation between the borehole tem-
peratures and the results of the mine fire diagnostic re-
sults, This may be due in part to a heat transfer problem
related to the location of the casing.

Laboratory results and other field studies support the
effectiveness and applicability of the Bureau’s mine fire
diagnostic technique in locating and monitoring abandoned
mine fires. The hydrocarbon ratio used to characterize
bituminous samples was not applicable to anthracite sam-
ples because of anthracite’s lower rate of hydrocarbon
emission and low concentration of higher hydrocarbons in
the desorbed gas. However, variations in the absolute
concentration of methane are considered an appropriate
indication of anthracite temperature.

The Bureau’s mine fire diagnostic methodology includes
(1) a single parameter that is characteristic of heated coal,
(2) a sampling method that qualitatively expands the sam-
pling volume, and (3) an interpretive method that defines
heated and cold areas. These factors make the Bureau’s
methodology a significant improvement in locating and
monitoring abandoned mine fires.

REFERENCES

1, Berztiss, A.T. Data Structures~Theory and Practice. Academic,
2d ed., 1975, 586 pp.

2. Chaiken, R.F., R. J. Brennan, B.S. Heisey, A. G. Kim, W. T.
Malenka, and J.T. Schimmel. Problems in the Control of Anthracite
Mine Fires: A Case Study of the Centralia Mine Fire (August 1980),
BuMines RI 8799, 1983, 93 pp.

3, Dalverny, L. E., and R. F. Chaiken. Technical Services to Ex-
tinguish the Mine Fire in the Abandoned Renton No. 1 Mine in Plum
Borough, Allegheny County, Pennsylvania. Rep. to OSMRE, Inter-
agency ‘Agreement HQ-S1-CT-6-01492, 1988, 62 pp.

Mine Fire Diagnostics and Implementation of Water
Injection With Fume Exhaustion at Renton, PA. BuMines RI 9363,
1991, 42 pp.

5. Justin, T. R, and A. G. Kim. Mine Fire Diagnostics To Locate
and Monitor Abandoned Mine Fires. Mine Drainage and Surface Mine
Reclamation (In Two Volumes). II. Mine Reclamation, Abandoned
Mine Lands and Policy Issues. BuMines IC 9184, 1988, pp. 348-355.

6. Justin, T. R, and A. G. Kim. Mine Fire Diagnostics: Carbondale,
PA. Rep. to OSMRE, Interagency Agreement HQ-51-CT-7-45011, 1988,
7. Kaye, D. Boolean Systems. Longmans, Green & Co. LTD., 1968,
8 Kim, A.G. Low-Temperature Evolution of Hydrocarbon Gases
From Coal. BuMines RI 7965, 1974, 23 pp.
. Experimental Studies on the Origin and Accumulation of
oubaiG Gas. BuMines RI 8317, 1978, 18 pp.

10. ___. Laboratory Determination of Signature Criteria for Locat-
ing and Monitoring Abandoned Mine Fires. BuMines RI 9348, 1991,
19 pp.

11, ___. Laboratory Determination of Signature Criteria for Locat-
ing and Monitoring Abandoned Mine Land Fires. Rep. to OSMRE,
Interagency Agreement HQ-51-CT-6-01535, 1988, 45 pp.

12, Michalos, A.C. Principles of Logic. Prentice-Hall, 1969, 433 pp.

INT.BU.OF MINES,PGH.,PA 29571


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BUILDING BUILDING | 27 |APARTMENT|
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29

Figure 12.-Communication test results. A, Suction borehole 3, B, suction borehole 26.


_— —1090
=

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apanruens|* | © Borehole
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A. cross section
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Borehole drill log data
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11407 BBB Rock © Borehole casing depth
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30 27 29 17 I2 16 31 28 26 23 13 4 2 1 3 6 B 10
BOREHOLE NUMBER

Figure 3.Geologic cross sections based on driller’s logs. Top, site map; bottom, cross
sections based on drill log data. A— A’, Presumed area of 1974 extinguishment project, BB’,
1,080 elevation behind apartment bulldings, C—C’, boreholes upslope of apartment bulldings.



INTRODUCTION

Abandoned coal mine and coal refuse fires are a com-
mon problem in the coal regions of the United States.
Areas where smoke and steam are emitted do not neces-
sarily occur directly above their subsurface origins. De-
termining the location and extent of these fires can be very
difficult. Aerial infrared methods are limited to deter-
mining temperature variations within a few inches of the
surface, and their interpretation can be complicated by
heat-absorbing features on the surface. Temperatures
measured at the bottom of boreholes are essentially point-
source measurements, and are only accurate for a rela-
tively small volume of the mine atmosphere.

To overcome the problems inherent in locating fires in
abandoned mines and waste banks, the U.S. Bureau of
Mines is developing a diagnostic methodology that com-
pares borehole measurements of temperature, pressure,
combustion products, and desorbed hydrocarbon gases
under natural or baseline conditions with values obtained

Borehole cap-

a

| / + — Monitoring

/ boreholes

when a suction fan is used to impose an underground
pressure gradient (1).4 It is assumed that mine gases tend
to flow radially from the surrounding underground areas
toward the point at which the suction is applied. Varia-
tions in a combustion signature at different points under-
ground are related to the assumed movement of combus-
tion products and heat from the source toward the suction
point. Data collected during the mine fire diagnostic study
at an abandoned mine site at Renton, PA, have shown that
measurable changes in underground pressure occurred at
distances up to 700 ft from the point of suction, and that
the average distance affected was 250 ft (3-4).

An illustration of the diagnostic technique is shown in
figure 1. In this figure, heated mine gases are being pulled

‘Italic numbers in parentheses refer to items in the list of references
at the end of this report.

Induced draft fan

> Mine gos

=D Mine gas plus
combustion products

a

—

Figure 1.—Mine fire diagnostic technique applied to abandoned mine fire site (artist's depiction).



MINE FIRE DIAGNOSTICS APPLIED TO THE CARBONDALE, PA,
MINE FIRE SITE

By Ann G. Kim,' Thomas R. Justin,? and John F. Miller?

ABSTRACT

The U.S. Bureau of Mines applied its mine fire diagnostic method to an abandoned anthracite mine
fire site in Carbondale, Lackawanna County, PA. The technique to locate fires in abandoned coal mines
and coal refuse piles includes the determination of hydrocarbon concentrations in mine gases, the
imposition of an underground gas flow direction, and use of a surface mapping method, to define heated
and cold zones in underground coal strata. The heated zones at Carbondale were characterized by
elevated methane concentrations. The results of 25 communication tests were analyzed to define 2 large
(approximately 100 by 250 ft) and 5 small, isolated heated zones. An approximate correlation existed
between the location of the heated zones and areas of anomalous snow melt. The correlation between
the results of the diagnostic test and subsurface temperatures was not significant.

‘Supervisory physical scientist, Pittsburgh Research Center, U.S. Bureau of Mines, Pittsburgh, PA.
2Blectrical engineer, Pittsburgh Research Center.
Mechanical engineer, Schneider Services, Inc,, Pittsburgh, PA.


14

LEGEND

© Borehole
[EZ] Heoted zone
|APARTMENT|

eunone | Qo EE) coid zone
3 E [Jno date

Scale, ft
Figure 13.—Combined communication results from tests at boreholes 3 and 26.

KEY

WZ Getcalated underground

+ COMMON
quadrant area

‘Combustion products
> | with flow direction
toward point [

Borehole with no measurable
combustion products
during suction

fo}
-@- 1 Suction borehole point |
e

Borehole with combustion
products during suction

Figure 14.Venn diagram as applied to results of communication tests,


32
4
°
4 0
2
°
5 9
7
2
° Oo 24
PH 28 °
26
JAPARTMENT] APARTMENT!
BUILDING BUILDING | 27 |APARTMENT|
BUILDING
S
30 @

29

LEGEND
© Borehole

Approximate snow melt
(Feb.12,, 1987)

° 100

Seale,tt

Figure 2.—Carbondale site map with snow melt areas and location of boreholes,

coal seams were present (fig. 3) at approximate elevations
of 1,005 and 983 ft. The topmost coal seam was about
75 ft below the surface. Upslope from the apartment
buildings, drill logs indicated the presence of coal in the
1,005- to 1,040-ft elevation interval (fig. 3), 60 to 100 ft
below the surface. Driller’s logs also indicated that most
of the holes had been cased through the top coal seam,

the most likely source of heating, and some had been
cased below the lower seam. Although there was concern
about the ability to obtain gas samples from the boreholes
that had been cased through the coal zones, pressure and
gas composition data indicated that this was not a factor
in the results of the study.

MINE FIRE DIAGNOSTICS

Application of the Bureau’s mine fire diagnostic meth-
od may be divided into three parts: (1) coal fire char-
acterization, (2) coal fire detection, and (3) interpretation.

COAL FIRE CHARACTERIZATION

Determining a suitable fire signature in the mine at-
mosphere is an integral part of the Bureau’s diagnostic
method. The concentrations of combustion products such
as carbon dioxide (CO,) and carbon monoxide (CO) are
frequently used as indicators of combustion. However,
variations in carbon dioxide concentration may be related
to chemical reactivity, the adsorption of water, the pres-
ence of bacteria, or other factors not directly dependent on

temperature. In laboratory studies, the concentration of
carbon dioxide did not always increase with increased tem-
perature (fig. 4). Although the production of carbon mon-
oxide is temperature dependent, the concentration of
carbon monoxide at temperatures below 120° C is relative-
ly low (fig. 5). Field measurements of carbon monoxide
also exhibit limited change with variations in borehole
temperature (fig. 6).

Previous research (8-9) by the Bureau has shown that
the desorption of low-molecular-weight hydrocarbons from
bituminous coal, methane (CH,) to pentane (C,H,,), is
strongly temperature dependent, and that changes in such
gas emissions are observable at temperatures as low as
100°C.


RI} 9421 REPORT OF INVESTIGATIONS/1992

Mine Fire Diagnostics Applied
to the Carbondale, PA, Mine
Fire Site

By Ann G. Kim, Thomas R. Justin,
and John F. Miller

UNITED STATES DEPARTMENT OF THE INTERIOR

BUREAU OF MINES


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5
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Oo 1000+
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0 — Je ‘ bd 1 i
0 50 100 150

TEMPERATURE, °C

200

Figure 6.—Concentration of CO versus borehole temperature, Carbondale site.

In laboratory studies (5, 10-12) of gas desorption from
coals and coal wastes, it was determined that as the sam-
ple temperature increased, the concentration of C, to C,
hydrocarbons in the gases that desorbed from bituminous
coals and bituminous wastes increased at a rate faster than
that of methane, the major hydrocarbon constituent. The
results of the laboratory tests with anthracite and anthra-
cite wastes indicated that hydrocarbon emission from these
samples was much lower than that from bituminous coals,
At the temperatures used in the experiment (less than
250° C) higher hydrocarbons (C,-C;) were not always de-
tected in the desorbed gas. However, the methane con-
centration had an approximate correlation with tem-
perature (fig. 7). Similar results were found in the analysis
of the gas samples from the Carbondale communication
tests (fig. 8). Therefore, changes in the absolute value of
the methane concentration were used in the diagnostic
procedure for the Carbondale mine fire.

COAL FIRE DETECTION

The restricted sampling volume of borehole (point-
source) measurements can be increased by several orders

of magnitude when an exhaust fan on the surface is used
to induce negative underground pressures. The pressure
differential causes mine gases to flow toward the point of
suction and across the borehole sampling points. An illus-
tration of this concept is shown in figure 9, Assume that
the exhaust fan is attached on the leftmost hole. If there
is communication between the exhaust hole and the neigh-
boring holes, a decrease in static pressure would be meas-
ured at the bottom of each borehole casing. If a fire exists
to the right of the rightmost hole (Case A), a combustion
signature would be detected in gas samples taken at each
borehole, Similarly, combustion signatures would be de-
tected at the exhaust borehole and one borehole in Case
B, and only at the exhaust hole in Case C. To verify the
location of heating, the fan is moved to another borehole
and the communication test is repeated. The successful
determination of combustion zones depends upon the abil-
ity to force and detect the movement of the gases from
these zones. Previous tests have shown that radially in-
duced pressure effects are detectable for a distance of sev-
eral hundred feet from a suction point. The lateral gas
sampling area from a single borehole in the underground
mine is thus extended from several square feet to several


0.8F
KEY

0.7 ANTHI
—b ANTH2
0.67 awstt
g.5L- Awste

0.4

COp CONCENTRATION, pct

50 70 $0 110 130 150 170 190 210 230 250
TEMPERATURE, °C

Figure 4.—Concentration of CO, versus temperature for anthracite (ANTH1 and ANTH2) and anthracite waste
{AWST1 and AWST2) samples.

0.08

KEY
—— ANTHI
O.06- + ANTH2
—*& AWSTI
- AWST2

0.04

0.02-

CO CONCENTRATION, pct

50 70 90 "0 130 150 {170 190 210 230 250
TEMPERATURE, °C —

Figure 5.—Concentration of CO versus temperature for anthracite (ANTH1 and ANTH2) and anthracite waste
~ _ (AWST1 and AWST2) samples.



through the area beneath a borehole that lies between the
suction borehole and the fire zone. A combustion signa-
ture can be measured at this borehole and the suction
borehole, The fire zone lies at or beyond the boreholes
showing combustion signature. The existence of unob-
structed mine entries is not considered crucial, since the
exhaust fan need cause only slight movement of under-
ground gases in order to be effective. Collapsed mines
and coal refuse piles can also be investigated with the
mine fire diagnostic technique.

Evidence of fire is based on measurements of the
changing mine atmosphere as determined from down-
borehole temperature and gas samples taken with and
without suction. A particularly sensitive indicator of the
presence or absence of fire is the change in concentration
of low-molecular-weight hydrocarbons that are desorbed

from heated coal. Increases or decreases in the concen-
tration of hydrocarbons with assumed flow directions are
related to the presence of hot and cold areas of the mine,
Using a borehole grid pattern and moving the point of
suction produces overlapping data “windows,” which can be
combined to produce a map of probable subsurface com-
bustion zones.

In February 1987, the Bureau, at the request of the
Office of Surface Mining Reclamation and Enforcement
(OSMRE), used the mine fire diagnostic technique at an
old mine fire site in Carbondale, PA (6). The 2-month
field investigation, data analyses, and the results of the
Bureau’s mine fire diagnostic technique are described in
this report. This work was done in support of the Bu-
Teau’s goal to minimize the impact of mining operations
on the environment.

ACKNOWLEDGMENTS

The authors acknowledge the following people who con-
tributed to the successful completion of this project: Tim
Walker and Donald McCann, Jr., mechanical technicians,
of Boeing Services International, Inc., who assisted with
the field work, often under adverse weather conditions;
Christina Manns and Andrew Miller, physical science
aides, and Joseph Slivon, Jr., engineering technician, of the
Bureau, who were responsible for most of the data entry
and/or equipment maintenance; and John J. Delaney,
John Sharkowicz, and Al Steber, engineering technicians,

of the Wilkes-Barre, PA, office of OSMRE, who contrib-
uted significantly to the timely completion of the field
work. The contributions of David Philbin, mining engi-
neer, Pat Acker, civil engineer, and John Holbrook, chief,
Anthracite Reclamation Program, OSMRE, who supported
the development of the mine fire diagnostic technology,
and Robert F, Chaiken, supervisory research chemist, of
the Bureau, who guided the development of the Bureau’s
mine fire diagnostic methodology, are also gratefully
acknowledged.

SITE DESCRIPTION

The Carbondale mine fire site lies within Pennsylvania’s
Northern Anthracite Field. The site is located adjacent to
an apartment complex in Carbondale, Lackawanna County,
PA. The complex consists of 11 three-story apartment
buildings built on an area that had been stripped and
backfilled in a previous fire control project. A 1946 city
dump fire had spread to underground coal mine workings
(2). Attempts were made to extinguish the fire in 1950 by
flushing and in 1974 by excavation, The excavation project
had been considered successful until recently, Although
there is currently some evidence of subsidence, the area
had not in the past been characterized by widespread vent-
ing, subsidence, or noxious odors, which often occur at the
site of an underground fire. Evidence of the suspected fire
was observed during winter months when unusual snow
melt areas were noticed (fig. 2).

The Carbondale mine fire site has 34 boreholes with-
in an area of approximately 8-1/2 acres. The boreholes

were installed in 1986 by OSMRE for monitoring pur-
poses, and were subsequently used for the fire diagnostic
study. Thirty-two of the boreholes were cased with 6-in-ID
casings and two were cased with 4-in-ID casings,
Geological records indicate that at least six coal seams
are found in the Carbondale area. The six primary seams
are the Grassy, New County, Clark, and Dunmore Nos. 1,
2, and 3, These seams are relatively flat lying. The drill-
er’s logs indicate the presence of two distinct coal hori-
zons, which may be either the Clark and Dunmore No. 1
seams, or the Top and Bottom Clark seams. Coal and/
or carbonaceous shales were found within the 1,045-ft
through 970-ft elevation interval at the site with the surface
elevation of 1,120 to 1,080 ft. Data obtained from the
driller’s logs indicated that during the 1974 fire extinguish-
ment project the top seam had been stripped and back-
filled from the area that is now in front of the apartment
buildings (fig. 3). Behind the apartment buildings, both


CONTENTS

Abstract .......
Introduction ....
Acknowledgments
Site description . .
Mine fire diagnostics .

Coal fire characterization .

Coal fire detection . .

Interpretation . . .
Conclusions ...........
References .

ILLUSTRATIONS

Mine fire diagnostic technique applied to abandoned mine fire site

Carbondale site map with snow melt areas and location of boreholes .....
Geologic cross sections based on driller’s logs .
Concentration of CO, versus temperature for anthracite and anthracite waste samples .
Concentration of CO versus temperature for anthracite and anthracite waste samples .
Concentration of CO versus borehole temperature, Carbondale site ......
Concentration of methane versus temperature for anthracite and anthracite waste | samples .
8. Methane concentration versus borehole temperature, Carbondale site .
Mine fire diagnostic technique .................
Borehole instrumentation cap for mine fire diagnostics . tee
11. Equipment used to measure borehole temperature and pressure and to
12. Communication test results ............00 cece eee e ae
13. Combined communication results from tests at boreholes 3 and 26 seees
14. Venn diagram as applied to results of communication tests . . .
15. Site map showing heated and cold areas inferred from Bureau’s mine fire diagnostic technique
16. Site map showing heated and cold areas, snow melt regions, and borehole temperatures .......

Pepe

Naw

5:

TABLE

1, Results of communication test at suction borehole 3.............. see e nee eeeeeeeeenee nesses

BSS comida \sHan

RaRSE

11


10

Compression
plug

Septum

Y,-in-diameter
ie nipple

Welds: ‘Neoprene
= gasket
+} Compression

t fitting
3-in-OD

plastic tubing ve

a

Figure 10.—Borehole instrumentation cap for mine fire diag-
nostics.

allows the placement of temperature and pressure and gas
sampling lines at or near the bottom of each borehole.

To measure the borehole pressure and to obtain gas
samples, a hollow 3/8-in-OD plastic sampling line (stain-
less steel for extremely hot holes) is permanently con-
nected to the instrumentation cap and is suspended to the
bottom of the borehole casing. A portable diaphragm
pump (fig. 11) is used to sample the mine gases via the
down-borehole sample line. Completely evacuated 20-cm?
test tubes with resealable septa are used to collect gas
samples. As mentioned above, pressure measurements
also utilize the gas sample tubing. A special borehole-cap
tee and septum arrangement facilitates both pressure and
sample measurements from the same port (fig. 10). Also
suspended along the full length of the casing is a thermo-
couple probe to monitor the temperature near the sample
point.

Once each borehole has been instrumented and base-
line measurements of temperature, pressure, and gas
concentration have been obtained, mine-gas airflow pat-
terns are altered by applying suction at one surface bore-
hole per test. These tests, which are referred to as "com-
munication tests," consist of (1) the use of an exhaust fan
in the mine borehole system, to cause mine gases to flow
toward the point of suction, and (2) the measurement of
the mine pressure, temperature, and gas composition at all

Figure 11.—Equipment used to measure borehole temperature
and pressure and to obtain gas samples.

surrounding boreholes. Since the interpretation of the
communication test data depends upon induced and meas-
urable changes in pressure and gas composition, baseline
measurements are obtained before the communication
tests begin.

INTERPRETATION

Data acquired during baseline and communication tests
are stored and presented in the same manner. A complete
data entry includes borehole number; data type (i.c., base-
line or communication); date; time; temperature; pressure;
and the concentration of hydrogen, carbon dioxide, oxygen,
nitrogen, argon, carbon monoxide, methane, ethane, eth-
ylene, propane, propylene, butane, and pentane. Table 1
summarizes the results of the communication test per-
formed while applying suction at borehole 3.

The diagnostic procedure used to locate underground
fire zones is based upon two primary assumptions: (1)
changes in the concentration of hydrocarbon gases are
principally due to the presence or absence of heated coal,
and (2) the suction fan influences the underground flow of
gases to a measurable degree. It is further assumed that
each communication test provides information within a
defined area adjacent to each communicating borehole, so
that each test with a different exhaust borehole will cause
mine gas to flow across the communicating boreholes at


The change in the methane concentration was used as
the signature for anthracite combustion at Carbondale. A
change of at least +5 ppm methane indicated an increase
or decrease in combustion products. Within the com-
munication contour, the boreholes exhibiting changes in
methane concentration were then marked. This entailed
drawing a 90° quadrant with a radius of 50 ft, the approxi-
mate distance between adjacent boreholes, on a scaled site
map for each of the boreholes exhibiting the methane
change, The quadrant apex was centered at the borehole
and the quadrant was drawn pointing toward the suction
borehole. With this quadrant size, an area of approxi-
mately 2,000 ft? is defined for each communicating bore-
hole per test. The quadrant angle (90°) and size were
chosen to define a zone that encompasses the radial flow
path at the monitoring point (borehole) during the com-
munication test.

Next, each quadrant was coded as to whether an in-
crease or decrease in methane was measured at the bore-
hole. Increases in methane concentration were denoted by
shaded quadrants, and decreases by hatched quadrants, for
each communication test. Figures 124 and 12B are ex-
amples of two communication studies that have been map-
ped in this manner. Figure 124 (suction borehole 3)
shows seven shaded quadrants that represent the areas of
at least 5-ppm increase in methane during the suction tests
conducted at borehole 3. The six hatched quadrants in
this figure denote the areas of at least a 5-ppm decrease
in methane concentration during suction. Figure 12B rep-
resents the results of mapping methane concentration
changes at each borehole during the suction test conducted
at borehole 26. When figures 124 and 12B are super-
imposed, the resultant diagram (fig. 13) begins to outline
regions of (1) heated coal, (2) nonheated coal, and (3)
undetermined zones (i.¢., zones for which inadequate in-
formation was available to make a determination).

In essence, the Bureau’s diagnostic technique utilizes
the Venn diagram (J, 7, 12) approach to zone (domain)
classification. A Venn diagram (fig. 14) represents, in
graphical form, the relationship between domains for
which logical equations can be formulated that uniquely
define the sets. In applying the diagnostic technique, each
zone or quadrant represents one set of vector data (i.e,
methane concentration change and flow direction) and the
combined results are determined by utilizing a predeter-
mined set of guidelines. When collating the quadrants
from all the tests on the site map, these guidelines were
followed: (1) when quadrants of the same type (i.c., hot
or cold) overlap, the total area includes both quadrants;
(2) when quadrants of different types overlap, the over-
lapping area is undefined unless additional tests sup-
port either of the defined quadrants; and (3) when the

quadrants do not overlap, but the nearest quadrants are
commonly defined, the region between the two is consider-
ed to be contiguous. Areas where data are lacking or in-
sufficient are unbounded and interpreted as unknown rel-
ative to the presence or absence of fire.

Figure 15 is the map obtained when the results of the
25 communication tests are superimposed. Several sepa-
rate areas of heated coal were located at the Carbondale
site. The large heated region includes boreholes 1, 3, 9,
14, 15, 26, and 27. Noncombustion regions were detected
around most of this area. However, the borehole spacing
to the north did not permit the acquisition of sufficient
data to determine where a cold boundary exists. This area
is of concern because it is adjacent to two of the apart-
ment buildings, The second major heated region includes
boreholes 8, 10, 11, 13, and 18. Noncombustion areas
were detected on all but the eastern side. The four bore-
holes (16, 19, 20, and 21) along this side were either out-
side the area of communication or did not exhibit changes
greater than +5 ppm methane during the majority of the
communication tests. A heated area was detected south of
borehole 17 adjacent to the eastern side of one building.
Positive combustion signatures were determined at bore-
holes 32 and 33 when borehole 4 was the suction point.
However, these boreholes lie on the periphery of the site
(ie., no boreholes exist beyond them) so the size and
extent of these combustion zones are unknown. Samples
from boreholes 28 and 31 also indicate combustion activity;
this area has been a region of venting, primarily at the sus-
pected rock fracture line. It should be noted that it is not
unusual to have noncontiguous areas of combustion activi-
ty. It is quite likely that the combustion areas at boreholes
9 and 10 or boreholes 26 and 18 are in fact separated by
areas in which there is no combustion. However, the neg-
ative signatures around boreholes 1 and 7 may be due to
the entrainment of fresh air through the fracture line dur-
ing communication tests.

The application of the mine fire diagnostic method at
the Carbondale site was influenced by the size, location,
and condition of the boreholes. All of the boreholes were
in place before the diagnostic work began. Normally, a
borehole pattern on 100-ft centers is drilled for initial
testing. Based on the results, subsequent patterns are
drilled to confirm the location of combustion zones and to
establish a cold boundary on all sides. Since additional
drilling was not an option at Carbondale, the extent of the
indicated combustion zones at boreholes 17, 31, 32, and
33 could not be determined. The distance between some
boreholes, ¢.g., between 1 through 4 and 32 through 34,
contributed to uncertainty with respect to the extent of the
combustion zone. Poor communication and relatively low
methane levels limited the information obtained at the


Library of Congress Cataloging in Publication Data:

Kim, Ann G.
Mine fire diagnostics applied to the Carbondale, PA, mine fire site / by Ann G.

Kim, Thomas R. Justin, and John F. Miller.
Pp. cm. — (Report of investigations; 9421)
Includes bibliographical references (p. 16).

Supt. of Docs. no.: I 28,22:9421,

1, Abandoned coal mines—Pennsyivania—Carbondale—Fires and fire prevention.
2. Coal mine waste~Pennsylvania—Carbondale—Fires and fire Prevention. I, Justin,
Thomas R. II. Miller, John F. III. Title. IV. Series: Report of investigations
(United States. Bureau of Mines); 9421.

TN23.U43 [TN315] 622 s—de20 [622.82] 92-6229 CIP



Report of Investigations 9421

Mine Fire Diagnostics Applied
to the Carbondale, PA, Mine
Fire Site

By Ann G. Kim, Thomas R. Justin,
and John F. Miller

UNITED STATES DEPARTMENT OF THE INTERIOR
Manuel Lujan, Jr., Secretary

BUREAU OF MINES
T S Ary, Director


100

go KEY
| —-— ANTHI

bh ANTH2
70F -- awstt
60b > AwsT2

Sof
40F
30F

CHa CONCENTRATION, ppm

90 70 90 110 130 150 170 190 210 230 250 270 290

——_________TEMPERATURE, °c
Figure 7.Concentration of methane versus temperature for anthracite (ANTH1 and ANTH2) and anthracite waste
(AWST1 and AWST2) samples.

600
€
a .
& 500+
z .
E 4007
< .
e
fe 300F
2
w .
Zz 2007
°°
o
¢ ‘1007 .
x
o . . "an

0 ote Pt n l

0 50 100 150 200

a TEMPERATURE, °C nn

Figure 8.—Methane concentration versus borehole temperature, Carbondale site.



different angles. As the number of tests increases, addi-
tional and overlapping information is acquired concerning
the presence or absence of heated coal around the com-
municating boreholes. The diagnostic method’s accuracy
is directly related to the number of communication tests
performed.

The information collected from each communication
test is graphically represented on a surface map by a two-
dimensional area surrounding each borehole. Delineation
of the hot and cold zones involves several steps. First, the
extent of communication during a test is determined by
calculating the change in the pressure at the bottom of

i

each borehole. A pressure change of at least 0.005-in H,O
indicates communication between any given borehole and
the suction hole. Next, using this value, a boundary line
delineating the area of communication is placed on the site
map using a commercially available computer software
program. This boundary defines the *window’ for which
valid information was obtained during the communication
test.

SCONTOUR: A Basic Contouring Program, California Computer
Products, Ine.

Table 1.—Results of communication test at suction borehole 3

Pressure Fan Methane Estimated
Borehole! change, effect change, temperature
inwo? ppm? regime
0.011 Yes “165 Cold
-20.240 Yes +108 (a)
+011 Yes 9 Cold
-.010 Yes 4 Not
+105 Yes “171 Cold
+003 Yes 63 Cold
+032 Yes +22 Hot
-051 Yes +12 Hot
-.046 Yes +11 Hot
060 Yes +6 Hot
~021 Yes 36 Cold
) No +1 NDP
“M15 Yes +324 Hot
+005 Yes 27 Cold
+.005 No 0 Not
~046 Yes +19 Hot
: -.036 Yes a Not
: ~025 Yes a4 Not
: -016 Yes 0 Not
. +009 Yes A Not
22 -.007 Yes 0 Not
23. +024 Yes a) Not
24. ) No () NDS
2. ~075 Yes a Not
26. 010 Yes +40 Hot
7. -018 Yes 0 No*
2B. -035 Yes 0 Not
2. ~022 Yes C) Not
30. +.009 No C) Nos
a. +018 No 0 No®
32 +.004 No +3 Nps
33. +001 No 13 No®
34 we -.030 Yes 0 Not
ND Not determined.

\Borehole 2 not sampled.
24 = increase; - = decrease.
Suction borehole,

‘Methane change Inadequate for a determination.
Pressure change (fan effect) inadequate for a determination.