Geology Reference
In-Depth Information
4 were isolation projects and 137 utilized some form of surface sealing (Jolley and Russell, 1959; Shellenberger
and Donner, 1979).
In the Western United States, 85% of fire-abatement projects were surface seals, due to the relatively low cost,
the topography of the area, and the lack of water needed to implement other methods (Shellenberger and Donner,
1979). Surface sealing or smothering was considered the most effective method, even though tests made several
years after the completion of a project indicated that the fire had not been completely extinguished (Jolley and
Russell, 1959).
Two surface seal methods were used. In the Missouri River drainage region, the fire sites were generally located on
accessible, flat to rolling terrain with a maximum slope of 25°, and the strata over the fire area contained
0.61
10 ft) of relatively thin, friable rocks that could be easily worked by bulldozer. The area was
sloped with a bulldozer to fill in large cracks and to grade uneven terrain. Then a seal was emplaced when, a
bulldozer starting at the lower perimeter of the fire area, made a cut along the contour. In succeeding upslope cuts,
the material was cast onto the previous downslope cut, producing a seal between 1.2 and 2.4m (~4
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3.1 m (~2
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8 ft) thick. A
diversion ditch around the seal area controlled erosion due to surface runoff (Shellenberger and Donner, 1979).
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In the Colorado River basin, slopes were steep and surface strata were massive. In addition to bulldozer cut and cover
methods, blasting was often needed to produce material suitable for sealing the fire area. Surface sealing under these
conditions was more labor intensive, more time consuming, and more costly. However, it was considered the most
practical and cost-effective method of controlling fires in this area (Shellenberger and Donner, 1979).
Anthracite Coalfields
T he Bureau of Mines gathered data on 103 major fires and 71 minor fires that occurred in active mines in the
anthracite coalfields (Figure 16.2.2) between 1850 and 1936 (McElroy, 1938). Twenty-two of the fires were
recurrences of older fires. Complete control of fires in anthracite mines was especially difficult due to chemical,
physical, geological, and mining factors. Some fires apparently continued to burn undetected for 15
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25 years.
Between 1945 and 1988, more than 50 fires were detected in abandoned mines of the anthracite fields of
Pennsylvania (Philbin and Holbrook, 1988). Between 1950 and 1978, the Bureau of Mines was involved in 26
fire-control projects at 17 abandoned mine sites. Five of these fires required 14 separate attempts to control the fire.
There were 10 excavation projects, which may have involved complete excavation of the fire zone or excavation of
a trench barrier, 14 flushing or injection projects, and 2 surface seal projects. In the anthracite region, excavation
was estimated to be 80% effective in controlling fires. While flushing projects were on average only 25% as
expensive as excavation, they were less than 50% effective (Table 16.2.2). Surface seals were apparently 400 times
less expensive than the average cost of excavation, but there was insufficient data to reliably estimate their
effectiveness (Chaiken et al., 1983).
Centralia Mine Fire
Probably the most well known of the anthracite-mine fires is that at Centralia, Pennsylvania. In 1962, burning
refuse material was discovered in an abandoned strip pit (Figure 16.2.3). Pouring water on the fire and blanketing it
with clay failed to extinguish the fire, which spread to the outcrop of the Buck Mountain coal bed. Since it appeared
that the fire was spreading rapidly, it was decided to excavate the burning seam until the limits of the fire were
reached. After 2 months, the money allocated for the project had been spent, and the fire had advanced beyond the
excavation (Chaiken et al., 1983).
The next project involved drilling 80 boreholes and flushing fine coal refuse to surround the fire. The breaker
refuse was supposed to fill voids and minimize the flow of oxygen to the fire. When funds were depleted, no
effective control of the fire had been achieved. In 1963, the Commonwealth of Pennsylvania attempted to excavate
an isolation trench around the fire. After 4 months, fire was detected on both sides of the incomplete trench.
In 1965, a two-phase project estimated to cost US$2.5 million funded by the Bureau of Mines, the Commonwealth
of Pennsylvania, and Columbia County, was approved. Phase I would include backfilling and sealing abandoned
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